Hello, Noob needs help with 3 372xpw, all ported, all blown, one by me.

[Dan_IN_MN]

This area on the piston....that's what is exposed to the intake port? Right? I'm not sure where I'm going with this....

 

[mtngun]

This area on the piston....that's what is exposed to the intake port? Right? I'm not sure where I'm going with this....

If I understand you right, all the saws you've examined appear to show detonation on the top of the piston, and scuffing on the intake side of the piston ?

That's pretty weird that they'd all show the same problem.

Did you check squish before pulling the jug ? If these are modded saws, I'm wondering if the squish was too tight ?

Intake scuffing could be sucking dirt. Did the intake boots appear squeaky clean ?

Thanks for the pics, they are interesting.

 

[nohandle]

The pic shown is the 2004 71cc piston on the intake side after running on the 2009 xpw crankcase. The 2009 showed up seazing atdc right before it turned over. Pulled the P/C 75cc (EDIT This cylinder showed obvious detonation and mushrooming of the piston) and found the intake side of the piston scarfed and the rings seazed. exhaust clean.

I took the C/P from the 2004 71cc and installed, with gasket, onto the 2009. It ran for about 20 seconds and provided the exact same damage (Edit: plus piston chip running down beside the pin and locking the rings). including a cute pile of aluminum shavings in the crank case (no clean area from detonation). this is the one i plan to frankenstein with different crank and new bearings.

I haven't ran the 2008 crankcase, i also think its cylinder is ok because one ring was pinched in the piston, but no piston cylinder scaring. thats the one i plan to rebuild with top end.(edit or eom piston stupid 51.4mm bs)

 

[srcarr52]

Scarring on the intake side is from lac of lubrication or from contaminates getting in through the air filter. If a saw has that much debris in it you better make sure you flush all the bearings well. I personally would split the case and put new mains in.

Be sure to check the squish before starting your next Frankenstein saw.