HELP! No compression on rebuild 600 SDI

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polarbear

New member
Hi, I need help with this mystery. Me and buddy just rebuilt the top end on his 600 SDI Skidoo. We had compression on the bench and once it was in the sled, we pulled it over a few times and then lost compression on both sides. The sled never started because the battery was not installed yet. The rings on the pistons do not indicate a top or bottom side in the instructions. They are spi pistons. We are sure we put the pistons in facing the proper direction also. Any help would be appreciated.

Brian
 
indy_500

indy_500

Well-known member
Did you hear anything out of the norm? Does it sound normal when you pull it over? When you say no compression, you literally put a compression tester on it and got 0? on both sides?
 
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thebreeze

Member
The motor will seem to "pull over" much easier with the primary clutch attached to the crankshaft, as opposed to turning it over on the bench without the primary on there. Did you actually test the compression, of are you just going of of feel?

Also, the rings are not seated properly if the motor has yet to run, but you should still get a decent compression reading.

In terms of the rings, they are almost always marked, but the marking can be difficult to see. They will be a pain in the butt to get into the piston grooves if installed upside down. It is EXTREMELY important that they are installed right side up. If you don't know for sure, unfortunately, I would suggest pulling them out and rechecking before running that thing.
 
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snowbuff

New member
There is usually a stamp on the ring, usually a letter, which indicates the top. When looking at the end of the ring, there will be a slight bevel, which should, from the inside out, curve upward. The ring pin in the piston goes to the intake side of the cylinder. If all that is correct, you may have a bad base gasket, or the o-rings on the head may not have been installed properly.
 
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polarbear

New member
Thanks for all the insight, we are going to pull apart the motor and check the rings. It sounds like they are upside down. Will post what we find. Thanks again for the help.
 
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polarbear

New member
Well, The winner is.....Upside down piston rings. Flipped the rings over,put it back together and it fired strong on the first pull. Thanks for all the insight!
 
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ezra

Well-known member
ok you did not know about ring direction ?did you not put a few top ends on in the last few yrs are you sure the others are dot side up?
 
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lenny

Guest
he came up and rode yesterday and the sled seems to run good, did 100 miles yesterday
 
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