Engines MTU 12V4000M71 Push Rods Used

I would change the rocker arms with the pushrods... Similar to a lifter that develops a wear pattern to the camshaft, the pushrod develops a wear pattern in the pushrod seat. If you mismatch the balls and seats, premature failure will result. ...

thank you for answering but, I said, all push rods and "adjusting srews" (where push rods are seating) have been changed 1000 hours ago on all four engines.

have a nice day

pa

We have the competition MAN as a duo in the 50 tons, 80 Feet planer of a client .

Some photos can help a lot. When your balls and seats on the rods show extraordinary wear, oil can be 1 problem. Or the quality is not sufficient, or the oil supply to the rockers and top of the engine is insufficient - oil transfer and viscosity can be an indication.

You also tell us not how old the engines are and what the history of them is. Clearance that ranges from 1 mm to .3 or .5 can also point to a soft mechanic or worn out elbow grease.

What RPM do you use them on?

Those MTU technicians, do they maintain and adjust always? Or do they have the honours to find the problems?

Check if it is wear or hammer that caused the problems. Ours have had no problems for 1800 hours, collected in 18 years. Just adjusted around each 500 hours.

But about engines as said before, I know nothing.

hi,

engines have around 6000hours each. This have been overhauled (W5) at around 5000h. all push rods and adjusting screws have been changed during this overhaul.

we are running engins around 1930 rpm.

thanks for your help

pa

Have you checked your valve springs? I think your valve springs could be to stiff and causing excessive tension on the valve train over all. Has your valve stem's been growing from stretching? Have you checked the valve stem's min/max height? What I've seen in the past, it sounds like your valve springs are to stiff and causing excessive tension and excessive wear. Someone could have replaced the springs with the wrong springs!! You really need to check all aspects of the valve train. And please, let us know what you find out,ok?

hi

all cylinder heads have been changed on all engines during the complete overhaul (5000h). new cyl heads are MTU spares

thanks

pa

I had the springs in mind too, but MTU is the engine that "allows" 2000 RPM, while each other competition product advises to "stop" at 1700 RPM.

You still do not give us the info we need: 1930 RPM for the engines?

How long in a row? What seas? Where in the world? Personally, I would NEVER use that engine - 30 tons - conventional "old" at 1930 RPM for longer than 5 minutes.

These conditions are only good to "hammer" everything, make springs lame, or in your case, "adjust" each part that can't follow the deadly beat (ing).

If you run these engines at 1930 RPM, and you NEED the speed, your vessel is UNDERPOWERED or far OVERWEIGHT.

As engineer, you can use your veto to bring your $700.000.00 engines towards a fire squad all the time.

If you had better conditions before, check the complete drive system. Are your engines used with gearboxes? In a Jet or propeller system? Emerged or cavitation?

You would be surprised how much feedback you receive from that water, you are sailing on- up to the tiniest part of your engines.

MTU are just as MAN from the same out spring. Racing costs extra. Only, I should opt then for a more modern concept engine top without pushing rods and use the engine that close to max. RPM, only in emergency situations.

Do you have RPM/couple and load/time charts?

hi,

we run engines at 1930rpm. these engines are sold to run 2000rpm but we decreased speed because of exhaust backpressure too high.

running 1930rpm make backpressure admissible.

the vessel is a high speed craft and we need this speed.

Vessel are always powered just enough to reach the speed writen in the contract signed with the shipyard.

This engines are sold by MTU to run at 2000rpm. We run them at 1930rpm. I am that running engines at idle speed will solve the problem but...

thanks again

pa

must be a reason that MTU engineers missed

for example , if they replaced the heads , did they fit the wrong head gaskets and have lost oil pressure feed to the heads ? If fast wear has occured it could be a lubrication issue

do you have identical problem on every engine ?

other item to check , remove one pushrod and have it tested by a lab for hardness , ask for factory spec but should be around 50 - 53 Rc hardness .

maybe MTU is sourcing their pushrods from a different outside contractor ?

I have seen precision shafts on mining machines that were manufactured and machined but someone forgot to send them for heat treatment , they should have been 55 Rc hardness but i measured them as only 18 Rc meaning they were still in annealed form

That manufacturer replaced every shaft on a machine for my client after i showed the test results

ps. fast wear rate could be expected in the running in period , did you adjust them after 200 hours ? , if they still keep wearing loose after 200 - 1000 hours then i think lubrication or poor quality material is the problem

hi,

thanks for helping.

The problem is not coming from the replacement of the cyl heads because before this overhaul, the problem was already existing (that's why we changed all push rods and adjusting screws 1000hours ago)

Yes the problem is same on all engines.

we think about hardness...

pa

Engines only had 5000 hours before rebuild? This seems like a very short time frame on an engine only is turning 1930 RPM, especially a diesel. I have seen 12000 hours or more on various units. I might suggest you have other issues that are causing wear. Do you do oil samples and testing. If so what are you seeing in the oil? What grade of oil are you using etc.

Roller rockers might be a good idea...

If you're running high backpressure, you're heating the valves, too. Combined with the stiff springs for high RPM, you may have surprised the engine designers and might be floating the valves, which will lower the pressure feed to the rockers. Maybe anti-scuff additive? MOS2 or similar? What else did the factory reps have to say? What's the reason for the need for speed? Is it commercial or macho?

sorry for misunderstanding. The vessel is a high speed ferryboat. Speed is commercial...

yes, maybe change oil we are now using mobil DELVAC 1640...but this oil is recommanded by MTU...

pa

these are nice engines, totally designed for high speed large boats. But is the boat an aluminum hulled cat?

AT 1930 rpm's you should be getting 2400 hp gross and 1500 at the prop.

You need to make sure the engine mounts are still 'resilient' as otherwise secondary vibrations from the hull/prop back to the block are going to make those push rods spin like tops.

After reading all the replies and not wishing to duplicate any of them I suggest that you acquire an ultrasound listening device as well as an adjustable strobe light and take a listen and look under power if possible to see what is happening. The ultra sound will allow you to hear what you cannot see and see what you cannot hear and the strobe light will possibly give some visual indication to the problem such as harmonics etc. You will possibly be able to see if push rods are flexing or valves are floating allowing hammering of the ball and socket seats. Everything should become clear especially at the rpm you are running.

I am still American and so my English is still bad too! (sorry, I couldn't resist)

Do worries, I work with the French all the time, bad English is a cultural norm, we are all used to it.

A few other things I would look at is the camshaft runout.

Vibration harmonics between the engines.

Driveline dampening.

I have always been amazed at what can effect and engine.

I had a 2.2L Mopar engine that kept fracturing flex plates. AFter replace 4 of them I found the machine key holding the timing belt sproket on the nose of the crack had "wallowed out: the key way and allow for an almost 4 degrees of slop in the sprocket. That small am,onunt of vibration transmitted and amplified throught the crank was enough to cause the flex plate on the other end of the crack completely through around the bolt pattern.

Good Luck.

If the pushrods and the adjuster screw balls were wearing prematurely surely it would be visible. ...

Were the cam followers/lifters also changed at the same time?

hello,

no cam followers were not changed...

pa

Pushrods have two ends.

Thinking aloud here....when the pushrods were changed the new ball on the lower end of the new pushrods won't be "matched" to the socket inside the old followers. This early lash growth may just be the pushrods seating themselves into the old followers.

Have you readjusted and put the engine back into service yet?

yes engines are running (for 1000hours now)

Rattling or "quiet"?

quiet

Problem gone perhaps? Could now be that the bottom ends of your new pushrods aren't so new any more.

Hind sight is always clearer...why didn't you change the cam followers when the pushrods were changed?

What prompted the decision to replace the pushrods in the first instance? Had you run out of adjustment due to horrendous wear?

Sorry to be a nit picker mate.

there is a break-in period for new parts, but they should stablize after a certain amount of hours. push rod length will vary due to temperatures changes. clearances are checked at maximim heat.

i doubt if it's due to wear. more likely you're checking the clearances at different engine temperatures.

are you certain that the lock nuts are not loosening under temperature? mark everything and check if they stay in alighment or move.

good luck from the usa.

Ok there are several different levels of rebuild in the John Deere factory spec. (Deere was my old alma mater) A complete overhaul includes replacing with new every matched and mated component of the valve train from camshaft and bearings itself to the spring retainers. No refinished, machined, "renewed" parts are used in a critical rebuild because of wear that is not visible. The only piece that can be reused would be the head casting itself and then only if the engine had not been overheated as the cause of failure and only after a thorough magnaflux/Xray and complete measurement then a complete remachining with new guides, seats, rocker posts etc. The valve train on the High powered diesel takes a tremendous beating and the stresses involved do degrade the physical stability of many of the parts causing unexpected wear conditions and failures.

With regard to another poster, roller rockers are a low wear option but again the entire valvetrain needs to be mated to those parts so they work together properly.

If the engine performance is critical then maintenance can be nothing short of perfect. Obviously cost is a consideration and taking the boat out of service to rebuild again may not address the issue so I hate to advocate for the HAL approach but I would recommend running until failure and then replace the heads as an assembly with factory new units and see if the problem continues. If it does, then you need to look at the vibration and harmonics angle several other posters have mentioned.

hello,

we finally changed all push rods and "balls" with new ones.

No problem appeared since 1000h running.

thanks for helping

pa