ShoerFast said:
Frank
As we all know that "dirt ingestion" would effect all the bearings somewhat the same. Throw in piston / cyl wear with inadequate lube.
Detonation would take a well engineered engines wrist-pin bearings a little quicker then the big end bearing,,,, as the rod would act a a slight angle with the little end taking the brunt.
It's so strange to see some of the ideas that are out there!
Kevin
EDIT : sorry, I pushed this topic slightly of course from just big end, but...
Not so sure... Wrist pin and big end bearings are needle roller type. Mains are "mostly" deep groove ball bearing bearings. The roller type are very strong with a high resistance to wear because of their larger surface area. Ball bearings have small point contacts on each ball/race that can wear or be damaged more easily.
I see some awful pistons/cylinders/cranks with ever sloppier big end bearing wear, but few (other then a spectacular welded big end on my 088) failures of the big end bearing. Almost all failures I see are main bearings.
The main bearing failures I see are from 1) dirt ingestion particularly on concrete or abrasive cutting saws, and 2) cage collapse. Cage collapse can be for many reasons, some of which are excessive temperature with plastic cages, possible softening of the carrier from fuel additive, and wear from dirt.
I've never seen a carrier collapse on a bearing that has a riveted steel cage (where there is a rivet in between each ball bearing), only in plastic cages. In concrete saws where bearing wear is always a problem Stihl uses riveted steel cages, the bearing can be shot, but the race cage is intact and the saw still runs! I'm constantly amazed at how bad these can be and still run well.
I have put riveted steel cage bearing in a number of saws - mainly the flywheel side where it's not a proprietary type. No problems...
Had an 036-pro yesterday with a reported rewind problem.. sure... the rewind was jambed, but... the flywheel side main bearing has collapsed, and the crankshaft BROKE off between the flywheel and the bearing. Nice... My guess - they ran it long after the bearing was bad resuting in cage failure, etc..
If anyone is looking for some interesting reading on mounting bearings and various failure modes :"Mounting and Dismounting of Ball and Roller Bearings" from FAQ Bearings Corp, Publication number 80100ED. 113 pages. I'm sure it's been updated since my copy so the Publication number may have changed.