Does anyone have a link to an article on the steps to rebuild the top end? or could somone list the steps with some pictures? I just need to put in a new piston and rings and i dont want to take it in becuase labor costs too much. I have rebuilt small engines before just not a snowmobile engine.

I don't have a link but I just redid the top end on my MXZ600 and suspect it is similar to yours. I'll try to recap the steps.

Remember to keep parts in order such as gear-side and clutch side carbs - not sure if this really matters but I do it anyways.

I also put whatever bolts, nuts, screws back into their holes once a part is removed. If I can't then I try to keep it with the part. This helps me remember what bolts are for what.

I also do not reuse any seals but buy a complete upper seal kit.
remove the airbox, pull off carbs and reeds
drain coolant into buckets by removing hose off of pump and head (watch it cause it can be messy)
remove coolant line from heads (one from reservoir and the other from the heat sinks)
remove spark plugs and head bolts (note two bolts above the exhaust port are shorter) and pull off the heads
remove sleeve bolts and pull sleeves off - generally you would check the sleeves for wear and out of round to see if they need cleaning up (honing or boring depends on the amount of wear)
cover crank opening with clean rags to prevent anything from falling into the crank
I needed to use a big c-clamp and sockets to push the existing piston pin out - watch from the needle bearings and retainers that may/will fall out (hence covering the crank area)
check piston ring end gap per instructions
install piston ring(s) per the manufacturer's recommendation
install bearings (how exactly depends on the type of replacement bearing you have - caged or uncaged), piston ring and pistons. I use a bit of grease to pre-lube the bearings and 2-stroke oil to lightly coat the piston and piston pin
install circ-clips per instructions
install gaskets (I used blue gasket sealer)
lightly lube sleeves with 2-stroke oil
line rings with pin on piston, hold ring close to piston and slide sleeve over piston - be careful to install the piston straight in not allowing the skirt to rub against the edge of the sleeve (repeat for second piston)
lightly install sleeve bolts
bolt on y-pipe to align the sleeves
torque sleeve bolts to spec (I usually build up to the required spec then recheck - once the heads are on there is no second chance!)
install gaskets, heads and torque to spec
install reeds and carbs
install hoses
lift front end so that air in the coolant lines running to the back can escape
open the air bleed screw on top of the thermostat and fill system with anti-freeze (I use a 60:40 ratio of anti freeze to distilled water)
close airbleed screw
leaving the coolant cap off I start the engine to allow it to warm up (at least until the thermostat opens)
Allow the system to run until the air in the engine and lines is cleared out
shut the engine off and allow to cool
adjust coolant level once the engine has cooled down
Keep an eye on the coolant level for a few runs in case an air bubble is still trapped

That's about it in a nutshell. Anyone please add anything I have missed. It is a long process to write out.

Merry Christmas.

I don't have a link but I just redid the top end on my MXZ600 and suspect it is similar to yours. I'll try to recap the steps.

Remember to keep parts in order such as gear-side and clutch side carbs - not sure if this really matters but I do it anyways.

I also put whatever bolts, nuts, screws back into their holes once a part is removed. If I can't then I try to keep it with the part. This helps me remember what bolts are for what.

I also do not reuse any seals but buy a complete upper seal kit. remove the airbox, pull off carbs and reeds
drain coolant into buckets by removing hose off of pump and head (watch it cause it can be messy)
remove coolant line from heads (one from reservoir and the other from the heat sinks)
remove spark plugs and head bolts (note two bolts above the exhaust port are shorter) and pull off the heads
remove sleeve bolts and pull sleeves off - generally you would check the sleeves for wear and out of round to see if they need cleaning up (honing or boring depends on the amount of wear)
cover crank opening with clean rags to prevent anything from falling into the crank
I needed to use a big c-clamp and sockets to push the existing piston pin out - watch from the needle bearings and retainers that may/will fall out (hence covering the crank area)
check piston ring end gap per instructions
install piston ring(s) per the manufacturer's recommendation
install bearings (how exactly depends on the type of replacement bearing you have - caged or uncaged), piston ring and pistons. I use a bit of grease to pre-lube the bearings and 2-stroke oil to lightly coat the piston and piston pin
install circ-clips per instructions
install gaskets (I used blue gasket sealer)
lightly lube sleeves with 2-stroke oil
line rings with pin on piston, hold ring close to piston and slide sleeve over piston - be careful to install the piston straight in not allowing the skirt to rub against the edge of the sleeve (repeat for second piston)
lightly install sleeve bolts
bolt on y-pipe to align the sleeves
torque sleeve bolts to spec (I usually build up to the required spec then recheck - once the heads are on there is no second chance!)
install gaskets, heads and torque to spec
install reeds and carbs
install hoses
lift front end so that air in the coolant lines running to the back can escape
open the air bleed screw on top of the thermostat and fill system with anti-freeze (I use a 60:40 ratio of anti freeze to distilled water)
close airbleed screw
leaving the coolant cap off I start the engine to allow it to warm up (at least until the thermostat opens)
Allow the system to run until the air in the engine and lines is cleared out
shut the engine off and allow to cool
adjust coolant level once the engine has cooled down
Keep an eye on the coolant level for a few runs in case an air bubble is still trapped
That's about it in a nutshell. Anyone please add anything I have missed. It is a long process to write out.

Merry Christmas.[/b]


Thank you so much. This is exactly what i needed. Your right, that was lot to write out, but i really appreciate it. Merry Christmas to you too!

Good luck. Post any questions during the build or at least that it's done and runs.

Enjoy the snow!

Good luck. Post any questions during the build or at least that it's done and runs.

Enjoy the snow![/b]


well it runs great now!!! i started tearing it down myself but i realized it did need to be bored out so i brought it to a local mechanic and he did the rest. I went to pick up the sled though and he said there is a gear in the crankcase i guess thats meant for the mountains???? new news to me. anyone know anything about it? he just said i should replace it with the right one.

well it runs great now!!! i started tearing it down myself but i realized it did need to be bored out so i brought it to a local mechanic and he did the rest. I went to pick up the sled though and he said there is a gear in the crankcase i guess thats meant for the mountains???? new news to me. anyone know anything about it? he just said i should replace it with the right one.[/b]


There is a gear in the crankcase, It drives the waterpump and oilpump. If your mechanic has it apart and says its warn, you might as well get it changed.

There is a gear in the crankcase, It drives the waterpump and oilpump. If your mechanic has it apart and says its warn, you might as well get it changed.[/b]


I'm not sure, but it sounded like he might have been talking about a gear in the chaincase, since he mentioned it was for the mountains. Like he was geared down too much. Not sure tho.

I'm not sure, but it sounded like he might have been talking about a gear in the chaincase, since he mentioned it was for the mountains. Like he was geared down too much. Not sure tho.[/b]

yeah sorry guys that was a typo...i meant chain case...whats the difference between this mountain gear and a normal one? just more low end?