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Unusual Stihl 044 conrod "failure"

popopboat

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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.

IMG_20231008_214558_788x1050.jpgIMG_20231008_214440_788x1050.jpgIMG_20231008_214437_788x1050.jpgIMG_20231008_214522_788x1050.jpg

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 ?
 

Wonkydonkey

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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, ?
 

legdelimber

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See if this leads to anything that helps.


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


Might be a few images here.

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.
 
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