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Discussion Starter #1
well i heard from some people that ur suppose to rebuild ur engine every 10 000 km and my mxz 670 is starting to get there. to get it rebuilt will probably cost around 1000-1500 dollars. so i was wondering how hard it is to rebuild ur own engine? i did it once in auto class with a 4 stroke but i know 2 strokes are quite differnt. i would be also boring it out 2 over to make it a 685 so i can get wiseco pistons and rings and the clips and everything for 300 dollars. then to take it in to machine it 2 over will cost probably another 50 dollars. but how hard is it to rebuild ur engine and are u actaully suppose to do it every 10 000 k? i would most likely take the engine out and bring it into my room over the summer to do it so i can have some time to do it right. to be able to order my pistons from royal they want you to know a lot of stuff. i will write it out after someone tells me how hard it is to rebuild it and if i would be able to figure it out. if i do end up doing i will be asking many many questions on here. thanks for any input.
 

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First off 2 strokes are much easier to rebuild imo, and taking your time is the best thing you can do. you may need special tools if you don't already have them.
 

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I wouldn't try it myself, if i where you i'd test the compression of the engine. If its still up there your piston rings are fine and there's no need to rebuild it. If it's not broke don't fix it. As for your 10k rule, my buddy has an 96 mach z with 15,000 kms on it and it's never been touched.
 

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Discussion Starter #5
so they say u should rebuild ur engine only if it has barely any compression left in it?
 

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Originally posted by The_Mad_Warrior
[br]so they say u should rebuild ur engine only if it has barely any compression left in it?
Anything under 90PSI you might want to rebuild.
 

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Rebuilding a 2-stroke is easy. I rebuilt an entire 800 triple having never done any engine work before at all. The only special tools you might need would be a clutch puller to get the clutch off and a flywheel puller to get the flywheel off. The pullers are about $50 each, but you only need to take the clutch and flywheel off if you are going to take the crankcase apart. What I did is disassembled the engine, pulled the crankcase out of the sled with the clutch and flywheel still on, then brought the case down to a service shop and had them pull them off... it took 10 min and they charged my $10. Other than that all you need is everyday wrenches and ratchets (you don't need special tools to put the clutch and flywheel back on). You will also need a torque wrench to properly torque everything to the correct specs when you put it all back together.

If the engine is still running good, I would just put in new rings and go. When you take it appart you can inspect the pistons for wear. If the pistons are good just have the cylinders honed (like $7-$10 bucks), slap in a new set of rings, new gaskets and go. Maybe $100 total? Unless there was an engine failure or your cylinders are out-of-round, you usually don't have to rebore.

Borrow a compression tester and test the compression of each cylinder when the sled is cold. The standard is to rebuild when the compression get down around 100psi. If your compression is good and the sled runs good, you probably don't need to do anything unless you wanted to do the rings just to freshen it up (I think 125-130psi compression is perfect for your sled, post in the engine forum to verify?) . Also you can take off the exaust and even the intake side and look in at the pistons to see if there is any scuffing or damage.

Anyway, I would not hesitate to rebuild it yourself, it's not that hard especially if you've worked on engines in the past. People on here can help with any questions. Also search the internet for 2-stroke rebuild tutorials, there are plenty of them. You may want to get a service manual, it makes life easier because it has all the torque specs and everything else... if you cant get one, post on here, I'm sure someone knows. I go to www.worldofpowerspots.com, then go into the repair parts section. They have all the engine schematics online. If you do rebuild, post pictures of the pistons and cylinders on here.

Have fun!
 

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Discussion Starter #8
alright thanks i appraicate the time u did to post that. im gonna do a compression test tomorrow or tuesday and see how it is. if it is good im gonna hold off on the rebuild until i get my indy 400 rebuilt. if it is that easy (not saying super easy just easier then i though) im gonna rebuild my indy which was leaned out so i may have to get it bored out then if i have to get it bored out what other things do i have to worry about? i know i have to get it machined, new pistons, new rings and then what else do i have to worry about?
 

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Originally posted by The_Mad_Warrior
[br]so they say u should rebuild ur engine only if it has barely any compression left in it?
Boy that is so wrong,,a 2stroke mill isn't like a car engine
they turn ALLOT more r's,for the distance you go
they should be reringed ervey 5-6K
and new slugs too if you want that motor to run 110%...
 

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I wouldn't hesitate to rebuild the motor myself. Last year was my first year of snowmobiling and I bought an Indy 400 with a blown motor and rebuilt it myself. The pistons, rings, bearings and gaskets for the top end were only about $130. The machine shop got $50 for boring the cylinders. I had a guy I know that works at a marine shop split the crankcase for me and press two new bearings on the crank (that was the reason it seized.) My friends MXZ 583 also burned down last year and we rebuilt that at the same time in my garage. We had never rebuilt a motor, and both sleds worked great when we got done. I'd go for it if I was you.
 

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I wouldn't do it if I didn't have to though. Listen to the other people that say to check the compression first. In my opinion I wouldn't do the top end without splitting the crankcase and checking the bearings and seals in there. If you're doing a preventative rebuild, I think it would be a mistake not to check over the bottom end and at the very least replace the crank seals.
 

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Discussion Starter #12
what do u do to the crankscase and such? i dont even know what the crankcase is. unless u mean where the secondary clutch attaches and there is the gears and chain that is the chain case is that what u mean?
 

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The crankshaft is what the primary clutch attaches to (and the flywheel on the other side). The crankshaft sits inside the crankcase is driven around by the pistons. Anyway, I took about 100 pictures and some videos when I did my rebuild. I'm going to post them on my website with descriptions sometime this week, you can use it for reference.

Go here and check out the schematics for your sled:
http://216.37.204.206/wps/Skidoo_OEM/Skidoo.asp?Type=12&A=237
 

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Discussion Starter #14
alright if i decide to do the rebuilt i am gonna check out those pics thanks for the help mmSeven
 
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