Cratered Motor help!

[troybilt]

Just got back from Little Sahara, and my buddy shelled the motor on his 86 ATC 250r. After tearing the motor apart, we discovered the piston skirt was broken... after digging deeper the tops of the left and right case was cracked too. Everything else seemed to be okay, no real play in the rod or crank bearings.

Does anyone know what causes the piston skirt to break? Would the shards from the piston skirt cause the cases to crack or would something else cause the cases to crack?

I read on here that there is a different length of piston bw. 86 and 87 pistons??? ...not sure there. We didn't do the motor work but the ATC the way it was, just noticed it was bored .020 over too.

Thanks for the help.

[Qracer]

A piston being too loose in the bore can cause them to break.

[Dave83]

The wrist pin location is what is different between 85-86 and 87-89 pistons.That more than likely wasnt your friends problem.If the piston was the wrong one for the rod,I dont think it would have ever ran to begin with.

[C-LEIGH RACING]

87/88/89 model piston on an old model short rod crank, the piston skirt will hit the crank.
More than likely clearance issues as already listed & to many rpms.
Neil

[troybilt]

Thanks for the help.

[troybilt]

Took some pictures, ...the crank and rod seemed ok, however he is having them inspected.
Not sure when the engine topend was rebuild.

Here is the pics. You can see a hairline crack on the case. Is that repairable?

Again, appreciate the help.

[troybilt]

another

forgot to add the pic

[troybilt]

again...

[troybilt]

one more time:

[86 Quad R]

yea that can be repaired.