Maggot snowmobile thread

[Gerome]

Ahh, I'm finally making progress on the engine rebuild. Even if I don't end up using my sled this season, I think it was worthwhile tearing it apart so that I didn't use it as its possible that I would have done some damage to the engine with 3,000 miles on it. There's a really nice crack in the original piston skirt that could have caused some problems.



I didn't realize that I would have better things to do than rebuild the sled this winter, like skiing, and playing in the sand with my 1.5 yr old kid. But I finally found some time last night to put the engine together. Two stroke engines are such simple machines, its pretty cool to take one apart and rebuild it.

[cmcrawfo]

Good on ya for taking this project on.

[kidwoo]

Hey bro you need some more oil lines with your oil lines, in case you run out of oil lines.


Nice find on the piston though. Maybe needed more oil.

[Gerome]

Haha, I didn't go anywhere near those oil lines, except to change the oil filter that connects to the oil reservoir. The crankcase had an inch or two of oil in it before I cleaned it out. No idea if that's good or not. I also assume the water and oil pumps will continue to work as well. Assumptions.......

I even got it bolted back into the sled last night! I was surprised at how light the engine felt without radiator fluid compared to when I lifted it out at the beginning of the project.

Things would go much quicker too if I slowed down. Instead I tend to bolt a part on, think it's symmetrical, realize it is upside down, remove and replace it, realize I didn't use lock-tite, pull the bolts again, then look up the required torque and then have to go back and torque the bolts to the right amount before moving on to the next part. Ahhhh, DIY!!!

[kidwoo]

Snowmobiles.

You know....

"fun!"


I think the insane amount of oiling is a carryover from Polaris not being able to make an 800 that didn't eat cranks up to that point. Not sure the outright bath is part of the design or not.. They definitely want oil getting in there to some significant degree though.

[cmcrawfo]

Haha, I didn't go anywhere near those oil lines, except to change the oil filter that connects to the oil reservoir. The crankcase had an inch or two of oil in it before I cleaned it out. No idea if that's good or not. I also assume the water and oil pumps will continue to work as well. Assumptions.......

I even got it bolted back into the sled last night! I was surprised at how light the engine felt without radiator fluid compared to when I lifted it out at the beginning of the project.

Things would go much quicker too if I slowed down. Instead I tend to bolt a part on, think it's symmetrical, realize it is upside down, remove and replace it, realize I didn't use lock-tite, pull the bolts again, then look up the required torque and then have to go back and torque the bolts to the right amount before moving on to the next part. Ahhhh, DIY!!!

I am rooting for ya bud ..... but if this thing pops in its first few hundred km, not too many would be surprised.

[kidwoo]

I hate to tell you this but before you got everything back together, you could have checked the oil and water pump functions.

A dead water pump will fry your sled pretty soon and you'll know once the temp shoots to the moon as soon as you start moving. You'll see temp warnings though. Both are driven by the crank though so you can still see if water or oil moves through the pumps by just pulling the cord and turning it over.



It's been so long remind me.....why did you take all that apart again? I mean I'm glad you found that fucked piston but that's going deep.

[Gerome]

It's a 2007 Polaris RMK 900 with almost 3,000 miles. I read somewhere that you're supposed to rebuild the top end on a snowmobile after 3,000 miles and the throttle response seemed just a little less snappy so it was a gut feeling between; do I try to get away with another 5 or 10 days this season or get it apart and do the required maintenance.

I've worked on cars since I got my drivers license and helped my stepdad work on my first car - a 1970 Datsum 240Z, and have driven a bunch of crappy old cars for a long time and drive watching the the radiator temperature, especially on my sled. Philosophy/pride/environmental impact of new crap/whatever leads me to almost always choosing to do maintenance and repair over buying the newest or greatest toy. To me working on my own sled is part of owning a sled. I'm mostly making fun of the way I double check my work.

Sure, I'm well aware I might miss something, and it all goes boom after throwing about $600 in parts and machine shop work, but I'm confident it'll go all back together fine. And that first pull on the starter when it turns over knowing I figured it out on my own is super rewarding.

What I'm confused about now is if the first 5 minutes to few hours are so critical to engine break in, do I run the engine to see if it runs, and bleed the bubbles out of the oil and radiator fluid while it's on the trailer, or do I have to wait until it's on snow to bleed the fluids then?

[cmcrawfo]

Just curious...Did you have adequate compression before you pulled it apart?

[Gerome]

There's a weird bleed off function on the 900 where when the engine runs it might hold 120-150 psi or so, but in order to use the pull start, the compression tops out about 90psi otherwise a person wouldn't be able to turn the engine over. At least that's what I've read and I had about 90psi in both cylinders prior to rebuilding the engine.

[kidwoo]

As it sounds like you probably know, compression is generally a ring thing so a cracked skirt wouldn't have shown anything. So it's good you dug in there. But to pull the entire motor? You must have done the crank and/or bearings too I assume? I had a 700 of the same year (same block, different jugs) and do remember something weird like that about the compression. I sold it after like two months though...... It just did weird things and I didn't know enough about sleds at the time to dig in.

As far as break in goes, once you get to the point you've got the head on, drop some oil in the plug holes so it has time to soak and coat everything as you get the rest back together. You can run premix on your first tank if you're worried about not getting oil immediately. As far as the coolant goes, fill up the reservoir and just pull the cord a bunch to cycle and keep filling until the volume stabilizes. Then run it a little, carry a gatorade bottle with some with you, and just keep checking it on your first ride. Some people prop the front of the sled up and run it at idle and just keep filling as it drains (not filling the resi while it's running obviously).

Did you completely drain all the oil lines? If so, I'd do a 1:50 premix for your first tank.

[pano-dude]

Joys of spring sledding, 2 km of mud to start the day..... wife was riding the old 670 and the sliders got so hot when she stopped to kick snow the rails stuck to the sliders.

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[simple]

From full stoke to full stop

[bbergey]

From full stoke to full stop

How long to dig out of that one?!?

[simple]

How long to dig out of that one?!?

Probably just under 2 hours. We all had wet feet by the end. I'm so sore today