Snowmobile World banner

1 - 9 of 9 Posts

·
Registered
Joined
·
195 Posts
Discussion Starter #1
Just did a ring job on the 485 fan. New rings, and gaskets on the top end. I "scuffed" the cylinder walls with 1000 gt sandpaper as they had no grooves and were nice and smooth. Initial compression reading BEFORE starting the engine was 100 psi per side after the ring job. Then I ran the engine for a few minutes and gave it some heavy throttle for about 3-4 seconds. Then let it idle for a couple of minutes and throttled it up again. In total, the sled was only running 5-6 minutes. Then I checked the compression again and each side was at 90 psi.
This seems really low for an engine with new rings. Could I have done something wrong? The compression before doing the ring job was 95 and 97 psi. I'm not quite understanding how the compression could be lower with new rings, with no sign of scratches or wear in the cylinder walls.
Any thoughts on this?
Thanks.
 

·
Registered
Joined
·
2,782 Posts
It should take about 3 to 5 hundred kilos to properly break in new rings unless you hone the cylinders with the correct angle crosshatch and finish. The type of ring also has a lot to do with break in duration for example chrome (Nitrided) rings are extremely hard and require a perfectly round cylinder to operate in and need time to seat into the bore.
 

·
Registered
Joined
·
2,782 Posts
No not bad and they are the same across the board so my opinion is that the gauge and conditions may be a little off. Leak down is the real test on a two cycle to ascertain health.
 

·
Registered
Joined
·
195 Posts
Discussion Starter #7
Just a bit of an update. Put about 80 km on the sled now, and compression is 105 psi per side. so it looks like everythings doing what it's supposed to be. If I can be around 115 psi. after the break in period, I'll be real happy. It's running strong, and I definately can't complain about the performance.
 

·
Registered
Joined
·
195 Posts
Discussion Starter #9
As I said... compression went up after 80 km. After about 200 km, compression is 115 and 116.... (give or take, cuz it's a cheap compression tester)
 
1 - 9 of 9 Posts
Top