Snowmobile Fanatics banner

1 - 8 of 8 Posts

·
Registered
Joined
·
232 Posts
Discussion Starter · #1 ·
Ive rebuilt my f7 top end last winter, and ended up with 125 or so psi on each cylinder. This summer I got a new sled and checked compression and it was at about 130 a piece, so I figured id rebuild the top end, ordered the same kit as last winter, from SPI and now after the rebuild and maybe ten min or so of running, 1 cyl has 120 and the others 130 psi.
Ive seen lots of people claim 140+ psi on sleds, is there something wrong with the SPI pistons? They were the cheapest I could find. or are these regular numbers for this soon after rebuild?
 

·
Registered
Joined
·
2,060 Posts
You wouldn't have needed a rebuild with 130. IMO- Compression should be over 120# and each cylinder within 5# of each other. With a 10# difference right after a rebuild I'd say tear it back down and re-check everything, sounds like a mistake was made.
 

·
Registered
Joined
·
2,422 Posts
/\ I agree, a rebuild wasn't necessary and you should tear it back down and see what went wrong.
 

·
Registered
Joined
·
8,842 Posts
going the absolute cheapest route is the first thing i would do, SARCASM.
i put spis in old sleds or for teenagers, but on a sled as new as an f-7 i would go with oem, wiseco, prox....
did you give the cylinders a hone job, or was the 15 dollars to much more to spend?

did you break the sled in properly? did you give it time to break in or simply bolted it together and checked compression.

pour some oil down the spark plug hole, then do a compression check, you will have your 140 back.
 

·
Registered
Joined
·
232 Posts
Discussion Starter · #5 ·
Alright Im gonna tear it apart again this weekend and inspect. I just dont want to have to deal with issues once the snows on the ground
 

·
Registered
Joined
·
1,179 Posts
is it even broke-in. rings take time to wear to the cylinders.
 

·
Registered
Joined
·
232 Posts
Discussion Starter · #7 ·
Well its only been ran for 10-15 min max, I took the more aggressive break in technique with this one, never reving til its fully warmed up tho
 

·
Registered
Joined
·
2,786 Posts
it takes 300 miles to break in a new top end. No wonder why your compression is low. Get some miles and then check it.
 
1 - 8 of 8 Posts
Top