[Sabian33]

Will be rebuilding my top half within the week here and just trying to get suggestions from other people on about every aspect of it.
Burnt up the PTO side and had some significant damage to the cylinder wall, other cylinder is fine.

One mechanic has told me it will be fine to bore out just the one side and leave the other one go, kind of skeptical about it, but has anybody ever done this or should I just go ahead and have both cylinders bored?

Next thing is a new Exhaust Valve since it took some damage as well.
I've looked and have only been able to find them running about $107, anybody know of a good place online to look?

Any help from anybody will be appreciated, i've rebuilt engines before, but just don't want to take any chances this time.[attachment=33494:IMG_1027.JPG]
If you look in the first picture, at the exhaust valve and port, that is where the most damage occurred.

 

[beaver670]

just did the top end on mine i would say do both mabe ask thumbdoctor he would give the best advice good luck

 

[NewfieBullet]

You can easily get away with just doing one side, and there's really no advantage to doing both, unless you got lots of miles on the sled and it kind of needed the refresh anyway.

I wouldn't put it back together without taking apart the bottom end though. As long as you're stripping it down you might as well check out the crank.

 

[Thumbdoctor]

Will be rebuilding my top half within the week here and just trying to get suggestions from other people on about every aspect of it.
Burnt up the PTO side and had some significant damage to the cylinder wall, other cylinder is fine.

One mechanic has told me it will be fine to bore out just the one side and leave the other one go, kind of skeptical about it, but has anybody ever done this or should I just go ahead and have both cylinders bored?

Next thing is a new Exhaust Valve since it took some damage as well.
I've looked and have only been able to find them running about $107, anybody know of a good place on line to look?

Any help from anybody will be appreciated, I've rebuilt engines before, but just don't want to take any chances this time.[attachment=33494:IMG_1027.JPG]
If you look in the first picture, at the exhaust valve and port, that is where the most damage occurred.[/b]

I would be checking your PTO crank bearing for cage damage. The bearing ball separators are plastic and don't like too much heat. Your failure root cause is probably a PTO seal brought on by the separator melting and all the balls going to one side or the other of the race hence elongating the crank seal. Rotate the crank very slowly and listen to the PTO side. If you remember hearing what sounded like a noisy clutch BINGO thats the sound of a bad crank bearing. The best thing to do is split the bottom and inspect the crank bearing and seals. Before you tear it down put the MAG side piston at TDC and mark the rotary valve position on the cases. Yes you can rebuild just one side with an oversize. The pistons all weigh in at the same amount and the crown is reduced to balance compression difference. The difference in power output because of increased displacement on one cylinder is negligible. Post a picture of your RAVE guillotine damage an I'll tell you if its serviceable (maybe I have a better one). The best steel caged crank bearings can be purchased from Atilier Adrien Bernard in Quebec Canada, They have been rebuilding cranks for years and know their stuff. Don't cheap out on crank seals.. use genuine Rotax. Don't mix piston types, if your going to do one side, stick with a cast piston so the warm up time will be conducive. SPX make a pretty good replacement piston which matches the OEM well. Might as well inspect the good side cylinder and piston while you have it torn down. Look for looseness in the piston ring positioner pin (or worn out). Check the ring groove and replace the piston rings (cheap insurance). Check your oil pump by chucking it onto a cordless drill and spinning it while observing output with the lever at full open (this will clear the 2 check valves). Check thickness of old cylinder base gasket (if its OEM, how many holes between the cylinders). You need to select the same thickness or spend some time measuring squeeze band .065 safe zone.

PM me if you need some specs or help.