Unusual Stihl 044 conrod "failure"

[popopboat]

Thought that this might be interesting.

An unusual failure with a Stihl 044 10mm.

Been rattling at idle, so i figured big end bearing gave out but NO.
Indentations from a bearing needles on the small end / wrist pin bearing side of the connecting rod.



This is a high-hour saw, but I've never come across something like this before. Typically, big end bearing goes AWOL, but in this case, there's absolutely no play in the big end bearing.

What are your thoughts on this ? What would have caused this ?

 

[redline4]

Are there matching marks 180 degrees to those?
I'd almost think that 2 of the rollers siezed, stopped rotating and just hammered into the rod.

 

[Powerstroke Cowboy]

What's the wrist pin look like?

 

[popopboat]

No other marks beside these on conrod.

Needle bearing is pretty much intact.

Wrist pin has only these 2 little marks.

 

[Wonkydonkey]

I,d say those two marks on the wrist pin stopped the rolllers on the little end from rotating and they wore those marks.

I'd think if you look closely at the wrist pin bearing it will be worn out differently on those two rollers

But I’ve no idea how the marks in the wrist pin got there, unless they were already there, ?

 

[Chainmale]

Could it have sat un-used for a while and bearing stuck in one spot long enough to get hammered when it was started again?

 

[redline4]

It could also just be poor metallurgy on the pin.
I see it happen to roller lifters in trucks, the roller galls and then it eats up the cam lobe.

 

[Yukon Stihl]

Happens a lot in Ujoints
Maybe run on 50:1 all its life

 

[legdelimber]

See if this leads to anything that helps.

Brinelling - Wikipedia

en.wikipedia.org

Some good explanations of what can cause the various types of bearing damage.
Well worth reading all of the types of damage!

Damage by Type

Troubleshooting - Damage by Type: If all conditions are known both before and after the failure, including the application and operating conditions, then a countermeasure can be determined by studying the nature of the failure and its probable causes.

www.nskamericas.com

Fretting

Services - Troubleshooting - Damage by Type - Fretting occurs at fitting surface and also at contact area between raceway ring and rolling elements. Fretting corrosion is another term used to describe the reddish brown or black worn particles.

www.nskamericas.com

Might be a few images here.

Fretting wear at DuckDuckGo

DuckDuckGo. Privacy, Simplified.

duckduckgo.com

I would think that area of the rod hole would be the zone for it to happen, due to the power impulse loading while the the rod is near the top of the stroke.
Any of the tiniest stray bits of metal, or pitting that it came from, will cause the rollers to bounce/bump/hammer and you begin to see an erosion of the surfaces.

It's why we aren't supposed to ever hammer on bearings or use a puller in a way that puts the pressure from one race to the other one. i.e.across the balls or rollers, as this puts tiny dents in the race surfaces.
Even if you hammer directly on the race that's holding/dragging, it still bounces/beats the balls or rollers against the races and leaves some damage.