Snowmobile Fanatics banner

1 - 7 of 7 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter · #1 ·
My 92 Formula Plus 580 chewed up the ring on the clutch side piston. Honed the cylinder .020 over, new piston. Put it back together and am getting lower compression on the replaced side (115 vs. 130 psi on the other), fouling as well. The head was beat up pretty good around the edges and I was wondering if thats my problem? I tryed to grind it smooth, but still has many pointed indentations. [xx(]
 
G

·
If you bored it out .020 over, make sure you installed a .020 over piston. We stuck a standard piston in a .020 hole one time by accident and it ran but had low compression and no power. Check the ring end gap. You may have gotten standard size rings on an over sized piston so the end gap would be to big. I don't think the little dents in the head is going to cause low compression. We put together several engines over the years with the same ring in the head problem you had and they worked fine. We just polished up the head and reinstalled it. Make sure you installed the piston the correct direction. There should be some sort of arrow pointing to the exhaust port. I would suggest boring out both Cylinder if you are doing one of them and replace both pistons and rings. You are working with only two cylinders so the expense in not to bad. On the older 6 cylinder outboard engines we would only do the bad one and leave the rest alone. Back then, 1980 $92 buck a piston plus another $30 for rings made it cost prohibitive to do all 6. The manufacurer would sell oversize pistons that were the same weight as standards and the compression ended up within 10 lbs of the untouched cylinders. Hope this gives you some ideas.

D
 

·
Registered
Joined
·
2,729 Posts
As D Noel is saying check for the correct piston and rings. But when you tried to smooth out the head did you remove material from the combustion chamber or just on the gasket surface? If you removed it from the combustion chamber, you have lowered the compression ratio and will result in a loss of compression. Also check to be sure the Choke isnt stuck on the carb that feeds that cylinder. 115 psi is still a decent amount of compression, not great, but enough to make the sled run fairly well.

TOU
 
G

·
115 lbs. That was kind of what I was thinking. NOt really to bad. If it has not been run much sence rebuild, the rings may not have seated properly yet. Run it some and see if you get any better reading. Also make sure that carb is opening up all the way when you check compression. If it is not in sink with the other carb. you could get different readings.

D
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #6 ·
Thanks for the responses. The piston and ring are both .020 over and the gaps are accurate, as is the piston direction. I suppose the loss of head surface in addition to the ring not being seated yet has caused the lower compression, which has stayed that way with several checks since. Strangely enough though, when I first put it all together, the new side piston was getting 126-129 psi. I ran it enuf to sinc the carbs, the collant temp got up to approx. 80 C.(pretty hot), and when I later checked the compression it was lower. I did bleed out all the air in the coolant, and it was around 50 F. OAT, too cool to get so hot. Might I be losing compression into the cooling system? I took the head off, how would I know? Is resurfacing(milling)the head the answer? It has a few scratches across the area the seals are made, but quite minor.
 
G

·
I don't think you would be losing compression into the cooling system. If you were, you would have noticed coolant loss and high pressures in your coolant system.

D
 
1 - 7 of 7 Posts
Top