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Active Contributor

Join Date: May 2009
Posts: 22

Camshaft Failure

05/10/2009 5:05 AM

We have (6.5 Mw Engine )- 400 rpm ,HFO 280CsT operated 4 stroke Diesel Engine supplying power to our power plant.

Last Year we faced a problem in the camshaft assembly in one of the engine ,near the fuel cam for cylinder head no . 1 ( I am attaching 5 pictures which depicts the location of the failure & the detail picture of the broken shaft. )location of failure.

one view of the failed camshaft.

the other portion of the broken camshaft.

another view..

We had a detailed discussion with the manufacturer & as per them torsional vibration is the only reason for such kind of failure of the camshaft assemblies, as during checking, we didnt find any other abnormaility with any part of the engine ie push rods , valves , rockerarm , fuel pumps , roller tappet assemblies for valves and fuel pump ,etc.

As per the Manufacturer , since the camshaft vibration damper were not replaced at the usual 8000 hrs , ( Failure of this camshaft occured at 39000 running hrs of the engine ), because of which damper didnt worked properly & caused high torsional vibration & hence the failure. ( even though there was no any abnormal vibration etc during the engine operation , before the failure ocurred )

Since there was no any other abnormaility in any of the engine parts, i have to believe that , camshaft vibration damper could be a possible possible reason for this brekdown.

Now i am facing a similar problem in one of my another engine ,which is having a fine hair crack at the same location- 2 cracks, where my first engine camshaft failure ocurred. (Manufacturer claims the same reason for this engine too as for this engine also vibration dampers were not replaced , running hours for this engine being 48000 hrs ) .

I have the following querries from all of you

1) Is there any other possible reason for such breakdown of the camshaft assembly.?

2)How much is the normal torsional vibration reading for the 4 stroke diesel engine (6.5 Mw ) - 400 rpm ( camshaft rpm - 200 rpm ). Presently we measure the torsional vibration in the engine from two magnetic pickups , one installed on the generator side & other installed on the engine side and both of them wired down to woodward 721 controller . Will the torsional vibration reading shown by 721 controller shows the torsional vibration coming on the camshaft assembly ?

3)Finally Can we undertake the repair of these two camshaft - one which is totally sheared off & the other camshaft which is just having two hair crack...( pl find below the picture of the same )Diameter of the camshaft is 150mm. length of the cam shaft assembly is 6 mtrs approx. Do anyone have any recommendation for the good workshop in the middleeast area / Europe / Asian region where similar kind of repair had been undertaken.

two cracks highlighted

Thanks & best Regards

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Anonymous Poster
#1

Re: Camshaft Failure

05/10/2009 9:18 AM

The 2nd instance of failure in the same location for the same part, which in this case is the camshaft, suggests to me that there can be a fault in manufacturing the camshaft, particularly related either to the material used for the shaft, and/or the processing;

If there was not an ample "Fillet" at the area adjacent to the large change in part diameter, it could start a fatigue "hairline" crack, which would progress to become a complete breakage due to torsional vibration/"hesitation", because of variation in the rotational momentum .

The repair of the already broken shaft is not possible.

The repair of the hairline crack on the other shaft, could be made with grinding the crack away, and then weld the groove with a tool-steel rod, preheating the area with the torch before filling it in.

But the manufacturer is correct about the replacing of the Damper, so as to keep active and smooth-out any jerking and shock-causing vibrations to the camshaft.

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#2

Re: Camshaft Failure

05/10/2009 11:19 AM

My opinion it's manufacturing mistake even he is right or not regarding his execrable torsional vibration damper. for similar engines assumed it has enough safety devices either to stop engine automatically or at least gives a certain signal for any up
normal running condition. like over heating, over speed and overloading safety devices also for low oil pressure protection device and other safety devices which either immediately stops engine in case of serious damage which may be a result of continue running or at least it gives a certain signal even sound or flashing light signal to draw operator attention that there is something wrong. Even human mistakes are considered in good manufacturing design. Your manufacturer tries only to escape from his responsibility. If the same problem had happened for both of your engines, be sure it's a common problem in all of his similar products. You don't need to repair the failure camshafts; I think you can get two new if you invite him for prosecution.
then you can ask him where is your safety device for over vibration.

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#3

Re: Camshaft Failure

05/10/2009 12:45 PM

Sorry I can't advise you on your problem.

I want to commend you on your well put question/presentation.

I wish more people could be as thorough as you.

Good luck!

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#11
In reply to #3

Re: Camshaft Failure

05/11/2009 4:02 AM

I totally agree, it makes a pleasant change to have such a good presentation...

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#4

Re: Camshaft Failure

05/10/2009 2:52 PM

Good afternoon.

1) Is there any other possible reason for such breakdown of the camshaft assembly.?

Desite your pictures and narrative, I am unable to determine how you know that the 2nd shaft is failing at "the same Location." Same location relative to what? if there was a keyway or something then yes we could reexamine the manufacturers advice.

What does same location mean to you? If you mean at a coupling, well, that might mean a number of other things...

If you mean at the same location ie by the fuel cam... In addition to to manufacturing or material issues, one might also look at design. However The manufacturer gave you an idea of expected life, which this particular item seems to have out performed by small integer multiples, so I would not be urging rudeness toeward the mfg.

2)How much is the normal torsional vibration reading for the 4 stroke diesel engine (6.5 Mw ) - 400 rpm ( camshaft rpm - 200 rpm ). Presently we measure the torsional vibration in the engine from two magnetic pickups , one installed on the generator side & other installed on the engine side and both of them wired down to woodward 721 controller . Will the torsional vibration reading shown by 721 controller shows the torsional vibration coming on the camshaft assembly ?

Don't know, but manufacturers advice should be heeded. Innocent until proven guilty.

3)Finally Can we undertake the repair of these two camshaft - one which is totally sheared off & the other camshaft which is just having two hair crack...( pl find below the picture of the same )Diameter of the camshaft is 150mm. length of the cam shaft assembly is 6 mtrs approx. Do anyone have any recommendation for the good workshop in the middleeast area / Europe / Asian region where similar kind of repair had been undertaken.

NO!

Nice to get a post that does its best to describe the problem.

milo

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#10
In reply to #4

Re: Camshaft Failure

05/11/2009 3:47 AM

Good afternoon to you,

1) After the failure of the camshaft for my first engine , the first thing i started doing in my all preventive maintenance activities is to closely monitor the camshaft assemblies of the other engines. ( Specially the same area where my earlier engine camshaft have broken ) So i found those cracks developing in the same location ie near fuel cam for cylinder head no. 1, ( first engine camshaft failure occured near fuel cam of cylinder head no. 1 ).

wishing your querries are clear

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#5

Re: Camshaft Failure

05/10/2009 10:22 PM

I agree with Milo The cracks origicnating from the even same portion does not mean a manufacturing error. As a manufacturer, we know that any rotating instrument is weakest at a point. The factor of safeties are calculated with reference to it and sufficient amount of it is put to attain the so called infinite fatigue life. However all these are based on the norma worst case scenariao. If your case, as you say that you have not replaced the vibration isolation, are worse that what I have designed, the above failure is expected. In fact it has proved by 39000 Hrs of life. The angle and the pattern do show the manufacturer's identification of the failure type. And the repetition of the failure zone too. There being a weak point does not mean that that is a manufacturing fault. In our examples, we always say the weak point is like a fyuse in home. Failure of the same fuse again and again does not mean you should increase the fuse wire dia. Only what normally we try in our machines is to keep the Couplings as fuse, so that it breaks in abnormalities rather than shaft. However this is not possible in all configurations, and even after a few couplings, the shafts do fail. Put the machine in order, follow the mfr guidelines. That is only recommendation. And welding of shaft: As I tell my customer, No. Welded shaft is not going to give you even a fraction of the life.

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#6

Re: Camshaft Failure

05/11/2009 12:15 AM

i think you said that the cam is 150mm dia? thats 6inches??? thats big..... looks like the cam lobes are pinned to the "cam" shaft that would be where i think tha the failure would have started. possiblly the pins came loose and caused the cam lobe to "work" back and forth on the shaft, which could start the crack. i can imagine that the lobes would be tight when checked after the failure, under opreating conditions the friction of the lobe vs the roller is a friction - heat producing point which could cause a loosening if the grip on the shaft. themal expansion. the other thing that i think i see is the failure is near the end of the shaft. you have bushing type bearings for the length of the cam and then you have what i imagine is a ball bearing. i am assuming that the alignment of all these housing bores is correct. but i see that the housing for the front,or maybe the rear, bearing is bolted on, i would be quite suspicious that the alignment amy not be correct there. also the engine looks quite clean sludge wise, good job. i wonder what condition that ball bearing is in. it may have had more clearence that the bushing type bearings that it is next to, or have worn to a larger amount over time, causing a larger bending force with every revolution of the cam. you said that this engine had a harmonic force gauge on it. but i dont think you said that anything about it showing any abnormal. i find it hard to beleive that a 200rpm shaft shaft speed would produce enough force to cause shaft failure. i dont know where you are in the world but if you are anywhere near seattle washington usa, try B and G machine. good luck hope i helped

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#9
In reply to #6

Re: Camshaft Failure

05/11/2009 3:38 AM

Dear Friend..

1)Your views have added a new line for me to think at..... your point is worth noting... Even i had a doubt on the looseness of the camlobes causes these problem. Like you said i found the lobes to be well placed in tight condition. My doubt on these lobes went fainter , because had there been any looseness in the Cam lobe, surely the firing ( Would have been retarded one or advanced one) would have been disturbed resulting in abnormal exhaust gas temperature for that particular cylinder head.( Which infact was not the case ).

2)Yes the dia of the camshaft is 150 mm and approx legth is 6 mtrs. The camshaft is resting on the Camshaft Bearing , The Camshaft bearing is a white metal shell bearing ( 2 piece design ) The bolts as seen in the picture are the bolt for the bearing cap for camshaft bearing. There is no Ball bearing in our camshaft assembly mounting. The camshaft bearing were also in the good condition showing no any abnormal rubbing or wear sign from outside / inside of these bearing ; which eliminate my doubt of any misalignment in the housing bores.

3)Even i am of the opinion that any welding repair job on the camshaft is not good option, The better option would be to ask the manufacturer to use my exisiting lobes & fit them on the new shaft making it a complete camshaft assembly.

4) As querried by some of other memeber , We use 380Cst HFO for our engine , after pretreament & preheating , the injection viscosity is 10 Cst ; Fuel injector nozzle opening pressure is 380 Bar.

5) As said by one of the member "I think you can get two new if you invite him for prosecution.
then you can ask him where is your safety device for over vibration

So is there any possibility that manufacturer could be brought to court for his failure in his design to install suffucient monitoring sensors for vibration , which finally lead to such heavy damage for the customer... Since never handled such issues before so requesting our fellow members to share their experience.

6) So till date i am assuming that camshaft vibration damper is the main culprit for this problem, I have already changed these dampers for my other engines. These dampers are basically viscous dampers,( high viscosity silicone filled )

any other views are most welcome.

thanks & best regards

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Anonymous Poster
#24
In reply to #9

Re: Camshaft Failure

05/12/2009 12:32 AM

hi again.... by looseness of the cam lobe i was meaning brinelling or galling at the contact area of the lobe-shaft press fit. if you have not removed the lobe from the brokrn piece of the cam you wont see that. also by looseness i only ment a shift of only the possible slack between the pin and the lobe. i realize that if the lobe had slipped more than a few degrees that the engine would have started running abnormally. as i assume that this engine is monitored quite closely. i am now wondering if the cracking is not caused by a stress riser at the point where the cam is drilled for the locating pins. this may be where the problem has started. also i am still suspicious of miss alignment if that rear bolt on housing. 39000 hours is good service life for most everything all tho i have to admit that i dont know much about big gen sets. 39000 hours at 50mph is..... let me figure.....thats almost 2 million miles in a car....... i would have imagined crankshaft of connecting rod failure first....... i dont think that legal action would go very far and i dont think that after you consider the things others have brought up you would be better off to offer this failure to the manufacturer for them to help make stuff better. i am sure that they want to see the parts and inspect them too. another thing is that this may have happened at assembly. a pin pushed too hard at assembly, a pin hole drilled slightly too small, a hole drilled too shallow,a pin too large of a diameter or too long, etc. i stiil find it baffling that a shaft that big could fail as it did buy just lifting valves that have relatively low spring pressure could cause enough twisting force to do what this did. am i correct that is the rear of the cam that broke? if it is the rear i there should be very little twisting force there. the injector pressure that petro brought up is something to ponder tho. i dont know that that those pressures can be that high for that big shaft either. does the cam drive some other system at the back?

i dont have anything to do with B and G machine in seattle WA, but i got a tour of their shop a few months ago after going to a machinery show recently. if you contact them i am sure that they could be of help.....

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#26
In reply to #24

Re: Camshaft Failure

05/12/2009 12:28 PM

i reread you post and saw that in fact that did occur at the front of the engine. now i see that it would have considerably more twisting and rebound forces. that would make it much more likely that any holes drilled in the shaft to fix the lobes on the shaft would be stress risers. i would be very interested in what the engine maker says what the cause was or some other independent inspector. keep us updated, i am very curious.

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#30
In reply to #26

Re: Camshaft Failure

05/13/2009 7:15 AM

Dear Wrench ,

1) YEs the failuire courred at the front end of the engine, the front portion is surely subjected to more of twisiting ie torsional forces.

2) I couldnt see any holes etc on the camshaft , as mentioned by you for the mounting of the camlobes.. As far my understanding , these cam lobes are shrink fit ... so where exactly these holes would have been drilled on the camshaft?

3) Manufacturer have already mentioned and pointed camshaft vibration damper to be culprit.Since the camshaft vibration dampers were not replaced at the designated running hours, hence the dampers were not dampening the torsional vibration which were arising in the cam shaft & hence finally leading to camshaft failure.


Thanks & Best Regards

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#27
In reply to #24

Re: Camshaft Failure

05/13/2009 6:45 AM

Dear Guest ,

Thanks for your comments..

1)As far as i understand , these cam lobes are shrink fit over the camshaft ...because as mentioned by you , i coudlnt find any pin / [in hole drilled over the shaft.

2) The failure of the first camshaft occured at the fuel cam for cylinder head no. 1 , The drive gear for this camshaft is installed near the cylinder head no. 1 end of the camshaft.

3) On the other end of the camshaft , is mounted the camshaft vibration damper.

4) Since this is a 6 cylinder engine, so the load which are comiong on this camshaft are

* Load of the fuel injector pump , its Roller Tappet & Fuel nozzle element of the pump.

* LOad of the roller tappet for inlet & exhaust valves + Load of the push road for inlet & exhaust valves + Spring pressure of the inlet & exhaust valve.

* So all the above loads comes on cyclic basis over the camshaft for each cylinder head. ( 6 nos ).

5) it is the front of the camshaft that broke ( ie the portion of the camshaft near the drive gear ) not the rear side.This camshaft doesnt drive anything else at the back.

6) For each cylinder head ,Roller tappet for fuel pump , roller tappet for inlet & exhaust valves rests over the respective camlobes.,

7) There is camshaft bearing betweeneach cylinder head , hence a total of 7 camshaft bearing( 1 bearing each between each cylinder head ) & 1 locating camshaft bearing( at the front end of the camshaft ).

8) The weight of the inlet / exhaust valves are not directly coming camshaft or the cam lobes.

thnaks &best regards

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#7

Re: Camshaft Failure

05/11/2009 12:42 AM

At first glance it looks like there is no radius ground at the transition of the shaft to the lobe. Also, I've never heard of a torsional vibration damper assigned to a cam shaft. It is true? So you have 3 TVDs ? Do you know what type of damper it is, such as Gieslinger 'finger' type (hydraulic) or is it a disc floating in jelly? The disc floating in jelly does not wear out, but, they do leak and perhaps the jelly changes viscosity with age somehow although I don't know how. If they are elastomeric (rubber and disc) then they DO need changing for sure.

Nothing will measure camshaft torsional vibes except a magnetic pickup or optical pickup reading that exact shaft to sense torque reversals like your two magnetic pickups do at both ends of the crankshaft. You cannot measure torsional vibes with displacement devices, however, torsional vibes can be assumed to cause a high lateral displacement via excitation of the vibrating component.

Fatigue failures take 1-2 million cycles to break, so, this is a recent failure of weeks not months. Each injection stroke, 1/2 RPM, is one cycle. So... what has changed in the past 6 months? Fuel? Load ? 280 cSt is HUGE for fuel injection. Viscosity at the injector tip should be about 12-15 cSt. Anything above that and it is too thick to spray through the nozzles and puts a VERY high camshaft load on the fuel injection pump. High viscosity normally blows the injection tips off. I would guess fuel coming into the fuel treatment skid is 280 cSt, then heated to something around 12-15 going into the injection pump (fuel rails). If you injection pressure is above 100 cSt I do not understand how you keep the tips on the injector nozzles !! The injection pressure design might be about 900-1000 barg if this engine is 20 years old. If it is newer, like 10 years old, it is likely 1500-2000 barg and if this manufacturer took an old model and just added different injection equipment to offer higher viscosity injection, they may not have studied the extremely high 'new' cam loads (a common mistake when offering higher viscosity range or higher injection pressures from a existing design). Ask for maximum fuel injection pressure design specifications for this model and compare it to similar model with lower injection pressures earlier. Then see if they have a different part number camshaft and cam gear (more robust). Get the drawings of previous and new cam to see if diameter changed and cam gear face width changed. To give you an idea of cam loads, a 900 barg injection pressure cam gear might be 10 cm wide and cam shaft 100 mm diameter. For 1500 barg, the gear might be 300 mm wide and camshaft 150 mm diameter. The full injection pressure ONLY occurs at full load (maximum fuel trapped in the fixed length injection stroke). So, if you have been fine at a lower load and just recently added more load, the cam shaft load will DRASTICALLY increase.

Call Wartsila and ask about in-situ repair. They bought a famous Norwegian in-situ repair company 10 years ago. Also, Google "In situ diesel engine repair" / ... machining / and various words like that but also include in-situ.

Check hardness of failed cam shaft at a laboratory and compare it to harness spec. If it is too soft, it breaks as you see, due to overload fatigue. If it is too hard, hydrogen sulfide stress corrosion cracking can accelerate an early failure. If your fuel has high hydrogen sulfide, and fuel leaks and fumes are in the cam box, there is a remote chance the shaft is too hard which makes it susceptible to stress corrosion cracking (harder is not better when exposed to hydrogen that is found in all hydrocarbons).

Some different thoughts at least ....

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#8
In reply to #7

Re: Camshaft Failure

05/11/2009 2:14 AM

Failure of first shaft 39,000 Hrs x 60 x 200 rpm = 468 millon rev

second crack at 48,000 Hrs

Both as far as the cycles are concerned point purely to fatigue failure

Also look at the crack propogation and the pattern, they to point at this direction, especially angle of propogation.

Fatigues are expected to start from these places (corners), the radius is available there if looked closely. And absence of dampers has increased the stress on the weak zone/

Due to this I agree with manufacturer,

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#13
In reply to #7

Re: Camshaft Failure

05/11/2009 4:09 AM

You wrote:-

At first glance it looks like there is no radius ground at the transition of the shaft to the lobe.

I noticed this too, but my impression was that it was two different parts, this was confirmed in a later post that they could be reused eventually on a new shaft.....

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#20
In reply to #7

Re: Camshaft Failure

05/11/2009 5:10 PM

Hi guys

One thing I agree with: the radius transition is a basic in Machine Design, especially where fatigue is at stake. No doubt there is a stress concentration at that section.

But, despite all other perspectives, I believe the crack started mainly due to Bending momentum (or moment ?), not torsion. If you think of the camshaft being bent as the cam gets its work done, we would have a cyclic bending momentum which, together with torsion, vibration and a bad design in diameter variation, would cause a problem.

At a rate of 200 rpm, we have 200x60=12000 cycles per hour. So, for 39000 hours, the total number of cycles will be 468 millions. Taking an infinite life limit of about 108 for steel, I would say the problem started well after the engine sartup and comissioning.

I believe the torsion momentum will contribute to the crack, especially in the case of the valve cams, which seems to be less round and more difficult to "climb". However, it appears that the crack appeared right next to the fuel pump cam, so my first thought was to this organ being malfuntioning, or pump change with no camshaft re-design, as petropower already mentioned.

Anyway, concerning the solution for this problem, I would go for an agreement with the manufacturer, trying to divide expenses... (how much are we talking about?). I would try to find arguments to have the manufacturer on my side, trying to solve my problem at the less expensive way, but making it an adequate solution. Maybe if there are any new projects at your company to press them into cheaply solving the issue, or some investments in the the power production field.

I believe that in these issues, unless there is a reliable alternative to the manufacturer, we must keep good relations and quickly solve the problem. Taking them to court will surely jeopardize any present or future deals and even your production.

Cheers

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#21
In reply to #20

Re: Camshaft Failure

05/11/2009 10:35 PM

The fatigue crack growth is too steep to be due to bending

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#12

Re: Camshaft Failure

05/11/2009 4:04 AM

Top marks for such a comprehensive question. If only all CR4 postings were as good!

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#18
In reply to #12

Re: Camshaft Failure

05/11/2009 11:32 AM

Agreed. I gave him a gold star.

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#14

Re: Camshaft Failure

05/11/2009 7:00 AM

Just have a look at this

http://materials.open.ac.uk/mem/mem_mf7.htm

And no, it is unlikely to bring the manufacturer to court.

It is as siple as that, recently my motorcycle had the drive chain loosend 2001 model. It is always serviced by the dealer. Should be once in 6 months ( along with oil change). I delayed to 12 months. Chain was visibly loose, but i neglected.

He had to change the sprocket. Can I go to the mfr for damages ? It was me who has not followed his instructions. So not worth it I feel.

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#15
In reply to #14

Re: Camshaft Failure

05/11/2009 7:35 AM

I do agree with the fact that its difficult to bring manufacturer to the court...

Another piece of information is that the OEM manual ( As Built ) which were supplied to us no where mentioned or instructed us to replace these camshafty vibration dampers at 8000-10000 running hours. It was just after we raised the issue of this problem to the manufacturer, they claim that these dampers needs to be replaced .. & then they forwaded me the sheet highlighting those instruction ... which incidentally was not there in the OEM manual received from them during project handover....

So is it possible to bring manufacturer to the court for not giving us the updated instruction manual for the replacement of camshaft vibration damper during the project handover time.

Dear SB , thanks for the link,There is a lot of similarity between the one in that and the one that of mine...

Thanks & Best Regards

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#16
In reply to #15

Re: Camshaft Failure

05/11/2009 11:17 AM

It seems unreasonable for the manufacturer to assume that the customer should intuit the need to replace the damper every 8000 hours (which, in some installations, would be roughly once a year). If the damper replacement requirement was not clearly spelled out for the customer before the failure, then the manufacturer should accept the responsibility for replacing the camshaft. Also, I wonder if the manufacturer can provide data from 40,000 - 60,000 hour engines which shows that frequent vibration damper replacement actually works to eliminate this failure -- perhaps the shafts fail prematurely even with regular damper replacement.

At the time when the engine was purchased, maintenance costs were, no doubt, considered in determining the overall value of the engine to the customer. Failure to spell out the damper replacement requirement at the time of purchase would be unfair to the customer.

I'd hope it is not necessary to bring the manufacturer to court, and that rather they would see the value of retaining customers, and understand that one unhappy customer can cancel out the good will generated by ten happy ones.

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#17
In reply to #16

Re: Camshaft Failure

05/11/2009 11:32 AM

An unexpected anti manufacturer post from a member who has otherwise been the voice of reason.

No dates have been provided for when the manufacturer may have put out a product notice. These kinds of updates "service bulletins" are the norm in many industries, cars comes to mind.

Until the manufacturer has been shown to be clearly negiligent, I am surprised to find you on the side of sue the bastards.

milo

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#25
In reply to #17

Re: Camshaft Failure

05/12/2009 1:22 AM

An unexpected anti manufacturer post from a member who has otherwise been the voice of reason.

Actually, it was not intended to be anti-manufacturer, nor am I in favor of suing the manufacturer. However, if the manufacturer did not make a concerted effort to ensure that the customer knew that the damper should be replaced every 8000 hours, then the customer would have a reasonable expectation that the manufacturer should make the repair, because torsional failure of a camshaft is not something that the customer should expect as a result of normal wear in an engine maintained according to the manufacturer's instructions.

Using the automotive analogy, suppose you buy a car in which the timing belt should be replaced (per the manual) at 80,000 miles. Suppose the manufacturer finds that the belts are actually frequently failing at 40,000 miles, due to an error in design. If the manufacture wants to retain customers, then they should pay for engine repairs if your timing belt fails at 40,000 miles and causes extensive engine damage. (As it happens, at that mileage, the repairs would be required by law to be free, because the camshaft timing relates to emissions control.) They should also issue a recall to correct the basic problem, because owners should not have to replace timing belts (a fairly expensive maintenance job) at 40,000 mile intervals.

In the current case, if the manufacturer can show that they contacted the customer with the requirement for damper replacement at 8000 hours, then they are off the hook. But if they failed to ensure that the customer knew the replacement was required, then they should accept responsibility for the repair, because the customer has the reasonable expectation that major failures will not occur if the maintenance schedule is followed.

I am not anti manufacturer at all, but rather offering an approach for the manufacturer to gain some customer loyalty. When I was a service manage for Honda, we'd often ask Honda to cover things (even long after the warranty had expired) if the problem was something you wouldn't expect to have happen on a Honda. They would invariably agree, and won many a long term customer by doing so.

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#19

Re: Camshaft Failure

05/11/2009 11:42 AM

With all respect for all viewpoints including that guy who attacked me, it's your opinion and I respect it.

Any how let us look for that topic from different view and by customer eye.

First

How many millions he paid for these engines? And suddenly start to fail one by one.

How much additional money he needs to pay again for repair?

How much he will lose for service interruption?

How much he is worry for what may happen tomorrow for other engines.

Are all these troubles not enough for manufacturer to install any kind of safety or warning device for over vibration?

Second

As you mentioned your O&M manual not mentioned any thing regarding this damper and what frequent it has to change, He declared that point after your engines had already failed

If it's an essential maintenance point, Why he hidden

Waiting answer for my two questions , as a customer not as a designer.

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#23
In reply to #19

Re: Camshaft Failure

05/12/2009 12:13 AM

Looks like I have ruffled feathers

As Milo said, based on experience, there are things that are added or subtracted and are given in the service bulletins, and are provided to the customers, to be added along with the O&M manuals.

Dampers to be replaced every 8000 Hrs - which boils down to once every year. In fact in the product we manufacture, there are a list of items to be replaced during every annual shut down. (No I am not related to the mfr, or even the type of product) and we keep on adding/ subtracting them as more and more product goes on line and the improvements take place to ensure the availability to customer.

There are millions of things that are assumed by the design person, but the equipment safety feature in MCMS are not put for all of these. The safety features are for those where most likely failure are to occur. However we see the things not happening as we want and a failure takes place due to a non potential cause, and we try to plug the hole. I had one of them a couple of years back.

The type of the failure as I said and even a link was given, clearly shows torsional fatigue. The angle of fatigue growth is clear as the root cause.

Now only the question is whether the monitoring system was capable of picking the torsional vibration and give an alarm when they have overshot the limits.

That must be investigated by the OP with the OEM. Since here the question is not whether he has forgotten or neglected to put on the dampers. Even new dampers within the 8000 Hrs could have made the vibration overshoot the limits and the engine must have been protected against these.

Absence of the effective dampers are one of the main reasons of the torsional fatigues failures.

My advice to OP to check up the vibration analyser to check its effectiveness, get the max designed vibration from the OEM (we provide these in the manuals) and if the existing MCMS (machine condition monitoring system) is not suitable, replace it with a better one. The question here is not the two shafts that has failed. It is the future - next year and so on the shafts that will fail.

a few links, one very old,

http://www.enginehistory.org/NoShortDays/TV.pdf

http://www.metaldyne.com/metaldyne/sections/engine/documents/brochure_dampers.pdf

(As a manufacturer, we have to protect our interests , but we do try to protect our customers )

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#28
In reply to #19

Re: Camshaft Failure

05/13/2009 6:54 AM

Dear Khairy,

I totally agree with every single word you wrote ... Infact i felt like all those words coming out of my heart.

The things which hurts me most is that , i had been religiously following every single maintenance instruction as supplied in the OEM manual,I had been so happy to maintain my engines so well untill the date this failure ocurred.

IN many of the engines vibration damper is mostly on the crankshaft , I dont know if all the engines have vibration damper on the camshaft too :??

Its just that i am bearing the consequences of someones stupidity ( the one who forgot to put the mainteenance instruction for the camshaft vibration damper in the OEM manual ).

Anyway raised this issue to brianstrom to see if any possible reason other than the camshaft vibration damper could be there.... so that i can prevent the same in my other engines.

And my fellow friends, hope you learnt the lesson of maintaining vibration damper with care.

Thanks & best Regards

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#22

Re: Camshaft Failure

05/11/2009 10:58 PM

I myself would not bother to atempt welding the second shaft untill you confirm its manufacture process. I can not be certian from photos but the pattern of the compleatly broken unit would lead me to suspect that it was eithor case hardend or subjected to some other surface hardening process (the protruding semi cylindrical section looks familiar)

Weather or not the manufacturer should assume responsibility is secondary to the repair and reimbursment can be sought after if so. I can tell that the lobes on your cams are definitly pinned and most likely were installed by heating them while freezing the shaft. as this would induce the least amount of stress durring install, and provide you with the most feasable means of removal. If you choose to undertake replacing the shafts themselves and have the equipment to do so then a good place to start would be confirming the manufacturers recomendations on such. If you choose to remain amicable with them for a bit this would be easier to accomplish. A locally obtained shaft should be possible providing you have those specs. Otherwise you may risk potential for further damage.

If it were me I would ask the manufacturer to send out a feild service tech (trust me, If they recomend changing components after only 8000 hrs then they have someone to fix the breakage which occurs if such parts are not changed.) And when their tech arrives, hang all over the guy. Pick his brain on all aspects of your equipment. BE NICE and act a little dumb and perhaps he will let his guard down and provide you and your employer the info you need to persue recourse. (it works for me on occasion.) Also you will get a factory warrenteed repair, which lets you off the hook for potential damage as they are usually required to sign off on there work. Speaking of warrenties 39000hrs (even divided into three shifts) translates into 6.5??? years of service (an average work year is 2000 hrs for one shift or 6000 for three.) I can not presume to know what warrenty laws are there but this seems to be pushing it as far as seeking reimbursment. After the repairs have been made to the first two shafts start inspecting the others (an efficient way to do this is eddy current inspection as it will also detect minute imperfections below the shaft surface. And for god sakes change those dampers. Down time costs employers much more than the parts to make a repair. You said this occured last year didnt you? Also you mentioned that you moniter for tortional stress at the input of the generator and at the engine but you did not specify where on the engine. I have seen similar and other damping systems used on some inline engines for similar purposes. It seems they have different harmonics than V configurations. Are there sensors on both ends of your camshafts? It seems to me that this would be the best means to determine tortional stresses in that location. Perhaps installing such in key areas will help to detect further issues before they become destructive.

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#29
In reply to #22

Re: Camshaft Failure

05/13/2009 7:08 AM

Dear Crim ,

1) After the incident , I have already replaced the camshaft vibration damper for my other engines.

2) Even i am not aware of the manufaturing process for the camshaft assembly , BUt i presume that they all are heat treated.

3) "Weather or not the manufacturer should assume responsibility is secondary to the repair and reimbursment can be sought after if so. I can tell that the lobes on your cams are definitly pinned and most likely were installed "

Can you please explain me the technical term Cams are pinned... does it means the same like shrink fit...as explained thereafter by you... I dont see any pin in those camlobes.

4) We are planning to send the broken camshaft assembly , so as to extract the old camlobes and install them in the new camshaft, This way i would be able to use the old camlobes...

5) As per present scenario , i have a one magnetic pickup installed on the generator shaft & then comes the flexible coupling ( Between Enigne & Generator ) & then comes the engines timing gear ( ie on the crankshaft ) where the other magnetic pickup sensor is installed. Both the sensors are wired back to woodward 721 controller,Infact it is giving me the torsional vibration on the flexible coupling... isnt it??

There is no any sensor mounted on the camshaft , except the tachometer on the rear end of the camshaft , which gives the standalone engine speed ( ie 400 rpm ).

I assume that i should have the similar mangentic pick up installation on the both end of the camshaft assemblies inorder to calculate the torsional vibration on the camshaft...

Do anyone know any such sensors mounted on any engine which helps in predicting the torsional vibration on the camshaft & crankshafts.

Thanks & Best Regards

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#31
In reply to #29

Re: Camshaft Failure

05/13/2009 8:03 AM

1. What you have written shows no pinning (some times to avoid rotation, the cams may be fixed to the shaft by pinning - ie passing a pin through them radially, or using keyway+key. Anyway that was not likely in your case and your post shows that it is not. The pinning or keyway would have resulted in a very high stress concentration.

2. The 721 controller - does it have the torsional vibration analysis? it is a speed controller isn't it ? it is supposed to smoothen out the vibrations.

3. Go for a torsional measurement and alarm/trip quite a few companies sell the equipments for these

googling to find

http://www.lmsgermany.com/testing-innovations-increase-accuracy-efficiency-torsion-vibration-analysis

However a number of more are there. Look for an system which condition your machine condition wrt torsional as well as other vibration and gives you an alarm (our machines we feature a trip also in case it exceeds limit2 (alarm on limit-1))

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#32
In reply to #31

Re: Camshaft Failure

05/14/2009 1:54 AM

1) Yes 721 controller is the one controlling the Woodward governor UG 40( mounted on the engine) , which inturn controls the fuel rack for the engine.

Since two magnetic pickups one installed on the generator shaft and the other on the crankshaft gears ( engine ) are wired down to 721 controller , this microprocessor based controller calculated the torsional vibration which is coming over the flexible coupling between the engine & generator. IT just shows the torsional vibration reading, there is no any analysis or vibration spectrum shown by it.

2) Dear Sb .. thanks for the links...one must go through these links to have added information about the torsional vibration.

thanks & best regards

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#33
In reply to #32

Re: Camshaft Failure

05/14/2009 11:08 PM

It seems that the camshaft itself would benefit from torsional vibration monitoring. The torsional vibration of the crankshaft could induce vibration in the camshaft, but the camshaft, even if driven by a very smooth running source (like an electric motor) will have its own torsional vibration that depends on its stiffness, the timing and lengthwise location of retarding and accelerating pulses (opening valves, pumping fuel, etc.), rotation speed, etc. The camshaft is evidently more susceptible to torsional fatigue than the crankshaft, and so it seems like a good candidate for monitoring independently from the crankshaft.

Interesting that the end away from the damper failed. Maybe there should be dampers on both ends.

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#34
In reply to #33

Re: Camshaft Failure

05/16/2009 7:02 AM

Dear Friends..

As requested by some of our fellow members...

i am attaching three files which shows various dimensions about the lobes., between the lobes , between the camshaft bearing , drive end & free end of the camshaft for better background of the problem

Thanks & best Regards

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#35
In reply to #34

Re: Camshaft Failure

05/16/2009 8:09 AM

One interesting part is the fatigue failure is between the drive and the driven. Quite of a bit may be due to the driven gears ?

Of course the failure is in the maximum stress area and i am not sure why there were no damping on this side.

BTW - In our equipments (not in the engine side sorry) but whether it is in other large gear boxes, or even turbines, there is a coupling that is to damp out the vibration. And I don't remember the gears or even a gearbox solidly coupled to the turbines or other shafts.

Here the gear mechanism is mounted on main shaft. The gears do have their vibrations and that is directly now on the shaft overlapping with its. Is it normal in engines ? Just a bit of I don't know whether it is OK.

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#36
In reply to #34

Re: Camshaft Failure

05/16/2009 1:04 PM

well after seeing your last set of pictures i see three things that would concern me. the timing gear is too far from the first cam bearing. that gear assembly must weigh at least 500 pounds.(about 1000kg) if my scale is correct that is about a foot from the first bearing of about 500 ft/lb of torque. this has to be putting an uneccessary bending torque on the front of the shaft that is pivoting on the first two cam bearings and levered by the third cam bearing, in between is where the failure occured. the next thing is the timing gear seems to be attached in three different diameters. the id of the cam/timing gear, the center housing , and the red housing that is attached to the camshaft itself. i cringe at the accumulated tolerences that may be there to cause gear pitch diameter runout, which could cause more torque bending force as the pitch diameters move in and out form center of rotation. by the way, what is in that housing? does it have any function? the third thing is that the cam bearing halves usually have increased clearence at the parting line which may be allowing more bending of the shaft. i guess that you could check the timing gear for differences in backlash at several locations around the diameter. i would be curious about what an indicator reading change you would get with the cam gear assembly on the shaft and off at the location of the faliure. i realize that there are many things that can not be changed about location of the parts of the engine. i see that there is a gear that is closer to the blockfront face. i wonder why they are driving some thing else off of that gear? it would seem that driving the cam up closer to the first bearing would be much more desirable. the more is see of this,i doubt that "harmonics" is the problem. looks like just a plain bending force. i am not a expert but just a "hard knocks" observation.

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#37
In reply to #34

Re: Camshaft Failure

05/28/2009 1:27 AM

hi again.... talked to a friend of mine about press fits. he brought up that a press fit of the type you have on that camshaft is the same as a square corner being machined on a soild camshaft. he says that those lobes that are pressed on become "as one" with the bar that they are pressed onto. he says that there should be a radius machined on the shaft to a larger diameter, on to which the cam lobes should be pressed. just a thought....... please write back...... would like to know what your thoughts were on my suggestions. what did the manufacturer have to say about the problem, besides the vibration damper.......what kind of operation is this unit used for? what brand of engine is that? probably something that we do not have in the usa. very curious.....

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#38
In reply to #37

Re: Camshaft Failure

06/07/2009 7:52 AM

Dear Friends

Sorry for being off from my desk...

Here are the details as requested by you.

1) Engine make is MAK 6M601 C ; 6.5 MW ; 400 rpm , 4 stroke HFO /diesel operated diesel engine ; Engine Oil SAE40 oil.

2) Engine is used for producing Power ;6.5 MW capacity of the engine.

3) I have checked the broken piece of the camshaft ( near the fuel cam lobe) but i cudnt find any square corner machined on the solid camshaft.; Till date i am not aware as how those camlobes are being installed on the camshaft. Also i dont see any dowel pin which will keep that camlobe in position and wont let it rotate over the camshaft. If any of our fellow friends know exactly the installation procedure of these type of camlobes , then pl do share.

4) Till date the engine manufacturer says that camshaft vibration damper is the main cause for this problem..

5) YEs friends... to share with you, i received the new camshaft assembly ( Our compnay bought it...:(((.....) we have installed the same ; idle trial / commissioning is in progress.

thanks & best regards

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#39

Re: Camshaft Failure

02/28/2012 10:05 AM

I have worked with MAK engines extensively. I recall specific preventative maintenance to replace the camshaft dampers. These were 6, 8 and 9 cylinder up to 2000 kw engines. I would say the damper is a very under rated device that offers invisible protection to shafting and bearings. It wears out and requires routine maintenance. Not to scold but if you are running large expensive machinery and require reliability you should know quite a bit about damping and the wear aspects of dampers. Besides the crankshaft and gearbox there is the auxiliary drive equipment such as your oil and water pumps that are engine driven that are impacted by the effects of torsionals in your camshaft (mostly due to varying loads from the fuel pumps).

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