Broken compression rings

[JimH]

While removing the pistons during the tear down of the engine I found the top compression ring on the #1 and #4 pistons were broken and fell right out. Is this common? And what could have caused this? Also when I removed the bearings I noticed on some there are traces of paper on the back side of the bearing. This struck me as odd but having never rebuilt one of these before I'm guessing this is normal?? Any ideas?

 

[Bob]

The piston ring grooves MAY have been badly worn, contributing to the rings breaking OR a previous "overhaul" was done without removing the ridge in the sleeve at the top of ring travel, breaking the new rings when they slammed into the old ridge.

It is NOT normal to find paper behind the rod bearings.

For a reliable overhaul, you need to get the crank out, and have it "mic'ed", and re-ground, as needed, and have the "big ends" of the rods checked, and re-sized, as needed.

The machinist will also check the rods for strightness, and replace, and "fit" the "small end" bushings, as needed.

 

[Ken(Ark)]

Like bob said , the rings probably hit the old ridge . The paper was to shim the bearings to make them fit tighter . It sounds like a poor patch job .Its people like this that give us shadetree mechanics a bad name .

 

[JimH]

Thanks Bob, I was planning to have the crank done professionally as I'm lucky enough to have a shop in my area that specializes in 8Ns. I knew going in that there are some areas that are too crucial to a proper rebuild to be left to my fumbling skills. This guy will measure, turn if neccesary and tell me what size bearings to order, in my book thats worth every penny...

 

[ZANE]

Since paper was found behind the bearing shells/inserts you should have the rods re sized too or you could end up with a turned/spun bearing when you start using the tractor later. Using that paper to tighten the rod bearings probably distorted the rods.

That still doesn't necessarily mean that the crank needs to be re ground but a thurough inspection should be done to determine the condition of the crank mains and journals to determine if in fact it does need re ground.

Zane

 

[JerryCPP(WA)]

Another possibility is using cheap starting fluid. This problem is more common with diesels. I vote with the old ridge, since it sounds like someone did an "Economy" overhaul.