CR4 - The Engineer's Place for News and Discussion ®


Previous in Forum: Mechanical Part   Next in Forum: Degree Calculation
Close
Close
Close
35 comments
Associate

Join Date: Apr 2009
Posts: 32

Effect Of High Hardness In Piston Pin

06/14/2017 5:30 AM

Hi Everyone

I have some confusion regarding effect of high and low surface hardness of piston pins (Gudgeon pin)during piston assembly running in two stroke and four stroke engines.

Thanks in advance

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 18283
Good Answers: 1061
#1

Re: Effect of High hardness In piston pin

06/14/2017 6:31 AM

..."The most common material for piston pins in general is steel; the surface is often hardened to improve wear resistance, and the choice of hardening method will dictate the choice of material. There are two main choices for hardening - carburising (also known as case hardening) and nitride hardening. Both have a beneficial side-effect of imparting significant compressive residual stresses to the surfaces of the part, which in turn improve fatigue resistance compared to a part without these stresses.

Carburising steels are characterised by a low carbon content and additions of manganese, nickel and chromium; it is the low carbon content that allows diffusion of carbon into the surface. Nitriding steels have additions of elements such as chromium, aluminium and titanium, which are strong nitride formers. These nitriding steels are similar to - and in many cases the same as - steels that we would normally use to make racing crankshafts. There are a number of higher strength steels not necessarily designed for nitride hardening, but which it is certainly possible to nitride and which would make excellent candidates for piston pins."...

What particularly is the source of your confusion?

https://www.highpowermedia.com/blog/3342/piston-pins-material-choices

https://en.wikipedia.org/wiki/Gudgeon_pin

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Associate

Join Date: Apr 2009
Posts: 32
#2
In reply to #1

Re: Effect of High hardness In piston pin

06/14/2017 11:59 AM

Thanks for throwing light. I think I could not make myself clear in the first attempt. The process of manufacturing piston pin involves carburising and hardening low carbon steel pins in sealed quench furnace.The hardness after this process is 64-66 HRc and the pins are then tempered at 175 ° for 90 minutes. My confusion is if the designer has specified 65 HRc maximum hardness in the finish pin; what effect will it have in the engine if the hardness is more by 2-3 units or lesser than specified.

Register to Reply Score 1 for Good Answer
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#3
In reply to #2

Re: Effect of High hardness In piston pin

06/14/2017 12:13 PM

No effect, it will work better, and last a bit longer, as long as bad knocking fuel is not used.

How hard was it to install the pins while the 2 cycle and 4 cycle engines were running? Just kidding you a bit.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Associate

Join Date: Apr 2009
Posts: 32
#8
In reply to #3

Re: Effect of High hardness In piston pin

06/14/2017 11:02 PM

Haha ! Thanks James.

Register to Reply
2
Active Contributor

Join Date: Mar 2017
Posts: 13
Good Answers: 2
#4
In reply to #2

Re: Effect of High hardness In piston pin

06/14/2017 10:23 PM

Hardness will affect wear rates, obviously.

Also, nitriding and carburising cause dimensional changes (growth), which will need to be addressed in the final grinding.

Register to Reply Good Answer (Score 2)
Anonymous Poster #1
#5
In reply to #2

Re: Effect of High hardness In piston pin

06/14/2017 10:37 PM

"My confusion is if the designer has specified 65 HRc maximum hardness".

They are the designer.

Who are you, and what did they say when you asked them?

Register to Reply
Associate

Join Date: Apr 2009
Posts: 32
#7
In reply to #5

Re: Effect of High hardness In piston pin

06/14/2017 10:59 PM

My confusion is hypothetical. Since different designers specify different values. For similar application, different designers design differently. Put my curiosity on this platform to know the intent behind this and its illffects(if any), if their individual specs are not met sometimes.

Register to Reply
Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8217
Good Answers: 759
#9
In reply to #7

Re: Effect of High hardness In piston pin

06/15/2017 1:03 AM

Unfortunately the reality behind many design specs are that they're closer to having been pulled out of the engineer's ass than having been real life justified in any way.

I've been around enough designs of different things in my life to now have fairly good ability to tell right off with a design whether or not it was a mathematically derived/pulled out of their ass design Vs one made around practical real world material selection based on commonality of components or materials that can meet or exceed the required specifications.

It's like finding a structural frame member that's some odd uncommon dimensional size that's difficult and expensive to find, like a 5.75" x .438" beam that costs $20 a foot Vs a 6" x .500" beam that costs $5 a foot where the added size and weight would be of no concern to the overall design in any way.

By the as engineered math for the unit the odd 5.75" x .438" beam is sufficient and the closest by the book match even though in reality it's not a common easily sourced or mass produced and thusly cheap item like the slightly larger 6" x .500" one would to be.

Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 18283
Good Answers: 1061
#6
In reply to #2

Re: Effect of High hardness In piston pin

06/14/2017 10:49 PM

Well the hardness correlates with the tensile strength, as you go down the scale the steel loses toughness and becomes more susceptible to wear...

https://en.wikipedia.org/wiki/Rockwell_scale

https://en.wikipedia.org/wiki/Ultimate_tensile_strength

http://www.academicjournals.org/journal/JMER/article-full-text-pdf/AE7648A5598

http://cr4.globalspec.com/thread/86814/Gudgeon-Pin-Failure-After-7500-KMS

http://products.asminternational.org/fach/data/fullDisplay.do?record=930&trim=false

This is why we do quality control testing of parts....You want to find defects in your product before being faced with a multimillion dollar class action lawsuit....You should know everything about the parts you are producing for sale...

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply Score 1 for Good Answer
Guru

Join Date: Apr 2011
Posts: 6330
Good Answers: 231
#10
In reply to #6

Re: Effect of High hardness In piston pin

06/15/2017 11:00 AM

"....as you go down the scale the steel loses toughness...."

.

That is not universally true. You have to be pretty far down to a low hardness before losing hardness further yields lower toughness steel. Many high hardness states are not very tough. Brittle fracture will occur with relatively small deformations at high hardness. Toughness is the ability to absorb energy and requires not just tensile strength but also ductility.

__________________
Eternal vigilance is the price of knowledge. - George Santayana
Register to Reply Score 1 for Good Answer
Associate

Join Date: Apr 2009
Posts: 32
#11
In reply to #6

Re: Effect of High hardness In piston pin

06/15/2017 11:07 AM

OK. And in case hardness is more; then?

Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#13
In reply to #11

Re: Effect of High hardness In piston pin

06/15/2017 12:09 PM

It is a trade off between ultimate hardness, and ductile toughness (the opposite of brittleness). You are still in range with RH value only 1 or 2 units above limit, I think.

You should try it on a test stand to see if your piston pins last OK, as I suspect they will.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply Score 1 for Good Answer
Guru
Popular Science - Weaponology - New Member Fans of Old Computers - PDP 11 - New Member Technical Fields - Architecture - New Member Hobbies - HAM Radio - New Member

Join Date: Oct 2009
Location: Maine, USA
Posts: 2096
Good Answers: 67
#30
In reply to #2

Re: Effect of High hardness In piston pin

06/16/2017 12:01 PM

"My confusion is if the designer has specified 65 HRc maximum hardness in the finish pin; what effect will it have in the engine if the hardness is more by 2-3 units or lesser than specified."

The effect will be that the part is rejected by inspection, since it is outside of the tolerance specified...64-66 HRc.

__________________
Tom - "Hoping my ship will come in before the dock rots!"
Register to Reply Score 1 for Good Answer
Guru

Join Date: May 2016
Posts: 696
Good Answers: 37
#12

Re: Effect Of High Hardness In Piston Pin

06/15/2017 11:24 AM

Most often the specification an engineer chooses is based on a history of successful product. I designed two and four stroke product for a landscaping equipment manufacturer for ten years and surprisingly, many of the parts are commodity items. The valve cams for Shindaiwa, Robin and Honda 4-stroke trimmer engines were the same part for some engine displacements. The same was true for wrist pins, valves and retainers, ignitions and clutches.

We would set up a run of prototype engines, run several thousand hours on each in the test lab and then out in the field. Once it survives, moving the specs around is very tough once you have success in the field.

Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#14
In reply to #12

Re: Effect Of High Hardness In Piston Pin

06/15/2017 12:10 PM

So even one or two RH units high might get the shipment rejected, is that basically the end of the story?

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Associate

Join Date: Apr 2009
Posts: 32
#15
In reply to #14

Re: Effect Of High Hardness In Piston Pin

06/15/2017 12:13 PM

Haha. Back to square one. Reached where we started from!

Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#16
In reply to #15

Re: Effect Of High Hardness In Piston Pin

06/15/2017 12:24 PM

I guess you better scrap those parts and start back at the drawing board. On the other hand, how much would it really cost to test a few high RH ones, and see if they are good?

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Associate

Join Date: Apr 2009
Posts: 32
#17
In reply to #16

Re: Effect Of High Hardness In Piston Pin

06/15/2017 12:37 PM

The question was of effect of high hardness. Scrapping or not is inconsequential.

Register to Reply
Power-User

Join Date: Jul 2016
Posts: 345
Good Answers: 17
#18
In reply to #17

Re: Effect Of High Hardness In Piston Pin

06/15/2017 1:01 PM

Perhaps better to give your customer an idea of the realistic/economic capability of your process. I suspect a specification listing a max hardness probably had some history of snapped or cracked pins that showed no wear on the journal surfaces, as many above have noted.

Given the likelihood of impact loading in this sort of application, I think I'd pay attention to max hardness specs, though I wouldn't have thought that when first looking at this post...

Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#21
In reply to #17

Re: Effect Of High Hardness In Piston Pin

06/15/2017 1:18 PM

High hardness: less wear due to friction/abrasive in oil.

High hardness: greater tendency for shatter (brittle failure) upon shock impulse.

You weigh the result.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru

Join Date: May 2016
Posts: 696
Good Answers: 37
#19
In reply to #14

Re: Effect Of High Hardness In Piston Pin

06/15/2017 1:10 PM

On a lot of the commodity items, we counted on the suppliers QA program. All ISO 9001 qualified. We still got bit on occasion. You'd get a field failure, diagnose it and find something out of spec and then go chase through stock to see how far the problem ran. Having to change the original spec was a very rare occasion though. Usually the result of having bred a better version of idiot requiring an even better countermeasure.

Register to Reply
Guru

Join Date: May 2016
Posts: 696
Good Answers: 37
#20
In reply to #19

Re: Effect Of High Hardness In Piston Pin

06/15/2017 1:14 PM

We did find out that prison work crews were a great place to field test. If they broke the tool, they got a free break. We had one guy who could fail a drive shaft in less than 15 minutes. By the time we got a good 300 hour run countermeasure figured out, the unit would run over 4500 hours of normal use with no failures.

Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#22
In reply to #20

Re: Effect Of High Hardness In Piston Pin

06/15/2017 1:20 PM

Did that one guy use a sponge to fracture bearing balls?

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru

Join Date: May 2016
Posts: 696
Good Answers: 37
#23
In reply to #22

Re: Effect Of High Hardness In Piston Pin

06/15/2017 1:26 PM

His task was to trim between curbs and granite headstones in a cemetery work crew. He found the right spot to wedge the trimmer head in repeatedly at full throttle until the clutch slipped. Initially it twisted the end off a flexible cable drive shaft and then sheared off the clutch hub.

Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#24
In reply to #23

Re: Effect Of High Hardness In Piston Pin

06/15/2017 1:38 PM

Nice, that dude is a real piece of work.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru

Join Date: May 2016
Posts: 696
Good Answers: 37
#25
In reply to #24

Re: Effect Of High Hardness In Piston Pin

06/15/2017 1:54 PM

Turns out to be a win-win. We found the weak spots and he got his break.

Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 18283
Good Answers: 1061
#26
In reply to #25

Re: Effect Of High Hardness In Piston Pin

06/16/2017 9:24 AM

Weedwacker outboard from Cap'n Dave, next big thing sez he....it's all in the prop design.....

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#27
In reply to #26

Re: Effect Of High Hardness In Piston Pin

06/16/2017 9:53 AM

Now, if he just puts some outrigger floats on that little boat, he can stand on it instead of taking a knee.

Looks like a Captain Morgan rum knockoff commercial.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru

Join Date: May 2016
Posts: 696
Good Answers: 37
#28
In reply to #26

Re: Effect Of High Hardness In Piston Pin

06/16/2017 11:12 AM

You mean the Shindaiwa Cuise-n-Carry. A lightweight outboard made from a weedwhacker motor.

Shindaiwa sold a lot of brush cutters into South America. In the Amazon basin it was common practice for users to have a boat prop that they put on their brushcutter to propel their boat to work. Switch to the brushcutter for the days work and then put the prop back on to go home.

Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#29
In reply to #28

Re: Effect Of High Hardness In Piston Pin

06/16/2017 11:17 AM

Nice. That is what we refer to as progress for the working stiff!

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 18283
Good Answers: 1061
#31
In reply to #28

Re: Effect Of High Hardness In Piston Pin

06/16/2017 5:27 PM

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#33
In reply to #31

Re: Effect Of High Hardness In Piston Pin

06/19/2017 9:14 AM

That is a 2-stroke correct? Appears as if the idle adjustment screw is not set, or the mixture of gas-oil is too heavy with oil? What happens to the quick attachment screw on longer shaft, that can revert to edger/weed whacker/blower when not in the boat?

Darn, I left out the chain saw attachment. That thing should be the Swiss Army Knife of boat motors, except it ain't Swiss, and this ain't your mother's goldfish pond.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru

Join Date: Apr 2011
Posts: 6330
Good Answers: 231
#35
In reply to #33

Re: Effect Of High Hardness In Piston Pin

06/19/2017 7:40 PM

Needs a Hurst shifter.

__________________
Eternal vigilance is the price of knowledge. - George Santayana
Register to Reply
2
Power-User

Join Date: Nov 2009
Posts: 283
Good Answers: 54
#32

Re: Effect Of High Hardness In Piston Pin

06/17/2017 5:09 PM

Early '70's Chrysler Corp piston pins had a hardness grade that enabled the pins to very effectively scrape a deep groove into the cylinder wall when the cheap retaining clip broke (or more likely, was never installed) and the piston pin worked its way out the side of the piston.

I was surprised that the cylinder's spark plug would actually foul within 200-300 miles of city driving because of the low compression on the affected cylinder. I encountered three 318 V8's with that particular design feature.

Register to Reply Good Answer (Score 2)
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11499
Good Answers: 136
#34
In reply to #32

Re: Effect Of High Hardness In Piston Pin

06/19/2017 9:18 AM

We had a Dodge sedan with that very engine, in that time frame, and when it was new and for the entire time we had it, the power source was indeed reliable, did not use oil, and had more than enough power for burnouts on the ad hoc drag strip east of town.

The lack of performance on the strip might have been the push button automatic transmission, since it was automatic, and no Hurst shifted manual with a beefy clutch.

There was a beefy clutz behind the wheel.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Register to Reply 35 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

ANKUSH JAIN (6); Anonymous Poster (1); Carl_E (1); GJM (1); James Stewart (11); Jpfalt (6); rwilliams (1); SolarEagle (4); tcmtech (1); Tom_Consulting (1); truth is not a compromise (2)

Previous in Forum: Mechanical Part   Next in Forum: Degree Calculation

Advertisement