Advice please - Low compression in a snowmobile

newguy · #1 12-13-2021, 06:28 PM

The machine is an 06 ski doo GTX 550 rotax touring sled

Found out today 1 cylinder has 105psi…
Didn’t get to the other cylinder.
Is there any options besides a new top end? Crazy money!!

Any advice is appreciated. Thanks.

Who Da Fisherman · #2 12-13-2021, 07:09 PM

Quote:

Originally Posted by newguy

The machine is an 06 ski doo GTX 550 rotax touring sled

Found out today 1 cylinder has 105psi…
Didn’t get to the other cylinder.
Is there any options besides a new top end? Crazy money!!

Any advice is appreciated. Thanks.

Come back after you have tested both cylinders and make sure it is warmed up prior.
This is less then half the story.
WDF

HunterDave · #3 12-13-2021, 07:20 PM

I just had my ‘09 Renegade 600 Etec done. Cost close to $3k. PARTS are hard to come by with supply chain issues. Don’t be surprised by how long it takes to get the parts. I took my sled in for repair end of June and I got it back end November. Good luck.

elkhunter11 · #4 12-13-2021, 07:27 PM

Run the engine, let it cool, and test both cylinders with a proven gauge. If it's still 105psi, you will need to inspect the top end, and repair/replace whatever is required.

ghfalls · #5 12-13-2021, 07:38 PM

If you’re somewhat mechanically inclined, a top end is quite easy to do on a two stroke. Check with mots machining for parts. Watch a couple YouTube videos and I bet you could do it.
Good luck.

newguy · #6 12-13-2021, 08:37 PM

Thanks for the replies!!

fordtruckin · #7 12-13-2021, 09:20 PM

shouldn’t be too hard to find older parts on eBay or Amazon for a 2banger skidoo. Low compression my guess would be you need rings and pistons. Depending how bad the cylinders are scared maybe new jugs as well. As others have said check all cylinders with a warmed up machine and a good gauge and go from there. Good luck!

lmtada · #8 12-13-2021, 09:28 PM

Quote:

Originally Posted by ghfalls

If you’re somewhat mechanically inclined, a top end is quite easy to do on a two stroke. Check with mots machining for parts. Watch a couple YouTube videos and I bet you could do it.
Good luck.

X2. Mott’s is excellent for motor rebuilds. Crank balancing, bores, complete rebuilds.

rjlester · #9 12-13-2021, 09:38 PM

I've rebuilt a few sled engines, I currently have a Polaris 488 fanner with about 95 PSI on both cylinders. It was a quick "hone and re-ring" job I did five years ago. Sled runs fine as it is, has pretty good power and my kids love it.

Is your sled running poorly? What prompted the comp test? As was already mentioned, check the other cylinder.

If they are both 105 and it runs ok, I wouldn't be worried about running it this way, but we definitely need more details on your sled.

I've also had lots of work done at Motts, although I deal with a third party outfit that farms out to Motts.

spoiledsaskhunter · #10 12-13-2021, 11:23 PM

in addition to more engine info, it would be nice if you could give us some info on how it isn't running properly. there are a host of things that could be wrong with it that don't necessarily involve burned up cylinders.

marty gave me an old yamaha a couple of years ago that wouldn't start (thanks marty!) i did the engine rebuild myself after getting the cylinders punched to first over.....unfortunately the engine was just the tip of the iceberg, but marty would ask for it back if he could see/hear it now.

sorry for the derail, but my point is that we need more info AND can you do this kind of work yourself?

you can save a huge amount if you know how to pull wrenches.

TheFall · #11 12-14-2021, 09:26 AM

Yes more info would be great. I used to rebuild snowmobile motors in a shop, everything from kids sleds to super modded sleds.

What prompted you to check the compression? 105 cold is not super bad for cold if both cylinders are the same. How many hours or km are on the motor since it was rebuilt? Was it ran on the wrong fuel or out of oil? Do you bag on the sled all the time or just putter around? Also remember that premium fuel goes stale rather quickly, if you are trying to burn stale premium, the sled is going to run bad, knock and possibly melt a piston from pre-detonation (worst one I saw from bad fuel I could fit my thumb through the hole in the center of the piston, but that was a race sled not a touring sled)

Confirm warmed up compression and do you have a good gauge? or a princess auto special? When checking, did you pull it over a couple times as hard/quick as possible?

If it is still low, or too low for your liking, those sleds are really simple to do a rebuild if you have some mechanical ability. Take your time and mark everything, watch a couple videos. It most likely just needs a quick hone, a set of pistons and new rings. If the cylinders have any wear that you can feel with a finger nail, there are a couple places around that will bore them over and do a port job at the same time (used to be a couple hundred bucks, but much more expensive if they needed to be recoated and not bored, or if they have been bored out before I wouldn't advise doing it again, but each to their own). I advise getting a good torque wrench, but I have done them by measuring the length of the ratchet or wrench and using a fish scale and a bit of math to calculate torque when re-assembling.

I used to order my pistons from The Sled Parlor outside Carstairs, I am not sure what their supply is like right now but they used to keep common stuff like that in stock. Landon is very knowledgeable about those sleds as well, so he will probably be able to give you some advice.

If you decide to rebuild yourself, send me a PM and I can give you a couple methods for break in and re-assembly, I can tell you my personal preference but 2 stroke motor break in methods are sort of like dog trainers, everyone has a different opinion.