74 evinrude skimmer, blown motor - Snowmobile Forum: Your #1 Snowmobile Forum

evinruderider · 10-28-2009, 10:17 PM

i have a 1974 evinrude skimmer. last year i rebuilt the engine and put new pistons in and honed the cylinders after the last time it blew. last winter it burnt the pistons up gain. im stumped as to why it would do this. i heard that i might have to bore the cylinders out to elimanate port wear. if i did bore it out where would i find pistons for it? any help would be great

**RJ Gleason** · 10-29-2009, 12:10 PM

Did you also replace the crank bearing seals?

evinruderider · 10-29-2009, 06:36 PM

no i havent. all it would take to do that is split the case and remove the old ones, then put the new ones on right?

**RJ Gleason** · 10-29-2009, 06:43 PM

Yep, you have to be sure that there are no air leaks, that's what probably burnt the pistons to begin with.

gbryanton · 11-01-2009, 05:31 PM

It sure sounds like the crankshaft seals.Did you notice that the pistons were burned up more to the exhaust side of the piston top.If so that indicates the engine is running with a lean mixture that causes very high temperatures in the cylinders.R J seems to have the same idea .Hope this solves your problem as pistons can be costly to keep replacing.All the best to you!!!