Pistons

6400 is a ton of miles, and 105 is a bit low. Most #'s for the 800's are usually in the 120-125 range, not sure if the 700's should be similar but i imagine so. With that many miles, I would be looking at doing a complete rebuild top to bottom.

105 is a tired engine .

I picked up my 01 SUmmit 700 early last season, did my own compression check with a cheapy tester from Harbor Freight, got high 120's both cyl. I took my sled in for a clutch servicing and his (far better) tester got 140 and 141. My sled had about 2400 miles on it at the time and if I still have it next summer then I plan on doing a top and bottum end rebuild then.

As far as I can tell from surfing here and a more experienced buddy who has been riding Doo's for many years most people have done a top and bottum rebuild on these sleds somewhare between 3500 and 4500 miles so if your sled really has 6000+ it's past due for a rebuild.

With that many miles you should definitly do a bottum end if you are going to do the top end, some of the bearings in the lower case are packed with Iso-Flex grease and there is no way to replenish that except by cracking the lower case,. Many have reported lower case bearing failure at lower miles than you have on your sled so maybe you'll get another thousand miles out of it, and maybe just a lap around the parking lot but you are probubly riding on borrowed time. It's much cheaper to do the rebuild before the thing seizes than after it seizes and as the season really hasn't started yet you can still get the parts pretty quickly, not so easy mid to late season .

You can also pull the Y pipe and have a look at the rings if ya want (they have a history of flakeing) but with 105 yer definitly loosing power.

I had my topend fail at 6200km's, I pulled the bottom end apart took it in and had it checked it was fine, after I got it back together I was 132 compression after break in it was 125, If it hasn't failed yet I would do piston and rings and wouldn't worry about the bottom end.

borrowed time

do it right top to bottom if you plan on keeping it

montanasledhead said:

do it right top to bottom if you plan on keeping it

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My 700 motor had around 6000 miles when I pulled it. I tore the case apart every fall & repacked the bearing on the PTO side. I went thru many pistons, most of which were my fault. 105# is low, put new SPI pistons in it & repack the PTO side bearing with isoflex grease. I agree with montanasledhead, you are running on borrowed time unless you rebuild it.

Spi

SPI in my experience is a GOOD piston, highly recommend using the T-moly version if it's available for that engine.

yeah, check the crank over, I'm betting it needs new seals....if the crank seals go bad, lean motor and burn-down, more expensive in the long run than just getting it fixed before hand.