09 800 low compression one ride after rebuild

SeanYYC

New member
Joined
Jan 9, 2015
Messages
3
Reaction score
0
Location
YYC
New top end last season, installed fix kit and new jugs. Compression at 125, went for one ride then parked it for the season. Cleaning off the cobwebs tonight and did another compression test and im getting 100-105. Put a scope in there and one side has carbon on top of the piston and the other one is almost completely clean. Everything else looks good. Anyone have any insight?
 

Lund

Active VIP Member
Joined
May 4, 2013
Messages
3,728
Reaction score
9,184
Location
Vernon/Kelowna
New top end last season, installed fix kit and new jugs. Compression at 125, went for one ride then parked it for the season. Cleaning off the cobwebs tonight and did another compression test and im getting 100-105. Put a scope in there and one side has carbon on top of the piston and the other one is almost completely clean. Everything else looks good. Anyone have any insight?

Sounds to me that the motor never got broken in. One of the biggest mistake DIY make. Proper motor breakin is the NUMBER 1 most important and crucial time in a motor's life. It makes or breaks a good motor.
 

Mach1

Active VIP Member
Joined
Sep 23, 2015
Messages
935
Reaction score
773
Location
Kimberley
New top end last season, installed fix kit and new jugs. Compression at 125, went for one ride then parked it for the season. Cleaning off the cobwebs tonight and did another compression test and im getting 100-105. Put a scope in there and one side has carbon on top of the piston and the other one is almost completely clean. Everything else looks good. Anyone have any insight?

I would try run it for a bit and oil lube it all up, then test again just to make sure, good luck.
 

Lund

Active VIP Member
Joined
May 4, 2013
Messages
3,728
Reaction score
9,184
Location
Vernon/Kelowna
I would try run it for a bit and oil lube it all up, then test again just to make sure, good luck.

I don't think that will actually fix his unseated rings. The oil trick will raise the compression as the oil will seal the unseated ring and cylinder surface but once ran and cleaned off it will be back to the low compression state.
The only way to fix it "IF" the cylinder's and rings did not glaze is to run the shet out of it under load. Get the cylinder pressure's up and the rings pushing hard against the cylinder wall's to get them to seat in.


My suggestion is take the sled to an open area with a long steady hill. Get the sled up to operating temp. DO NOT waste anytime riding it. Point it at the hill and go WOT for about 10sec. off throttle to mid and allow the some heat to dissipate for about 10sec. Again WOT for about 10sec. allow the heat to dissipate. Do this for about 10-15 run's, then check your compression. If it doesn't go up, you will need to rering.
 
Last edited:

SeanYYC

New member
Joined
Jan 9, 2015
Messages
3
Reaction score
0
Location
YYC
I felt like I broke the motor in gently that first ride but this sounds like a strong possibility.
 

Merc63

Active VIP Member
Joined
Aug 24, 2014
Messages
1,677
Reaction score
2,426
Location
Alberta
Breaking in gently is the worst thing to do. You need good ring pressure against the cylinders to seal them. Always make sure you're at operating temperature and do hard short blasts like above.
 

Merc63

Active VIP Member
Joined
Aug 24, 2014
Messages
1,677
Reaction score
2,426
Location
Alberta
Does the low compression side have carbon build up? Carbon could indicate a rich or heavy oil burn. Does this engine have dedicated injectors for fuel or oil, if it does, could be malfunction. Or individual throttles? One could be opening more or less than the other. How does the plugs look?
 

SeanYYC

New member
Joined
Jan 9, 2015
Messages
3
Reaction score
0
Location
YYC
Breaking in gently is the worst thing to do. You need good ring pressure against the cylinders to seal them. Always make sure you're at operating temperature and do hard short blasts like above.

This is what I ment by "gentle".
 
Top Bottom