Just Did Top End Rebuild...Not Firing/Starting

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XxXskidooXxX

New member
I just rebuilt my 1998 Ski-Doo MXZ 500. Two new pistons (including rings, pins, circlips) and a gasket kit. Got it back together, both pistons have 115 compression but will not even 'pop' when I try to start it. Any suggestions would be appreciated.
Thanks!
 
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XxXskidooXxX

New member
Yup, ran great before the rebuild. I went wide open in a field a little to long, the piston got to hot so the rings stuck/melted to the piston, so we rebuilt it.
 
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xcsp01

New member
May be beating a dead horse, but cylinder's where good? Hone them at all? Put the pistons on with the arrow facing the correct way? How long has te gas been in the tank of the sled?
 
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anonomoose

New member
Do you have spark? If so then timing is off...go back and put it together with timing marks in the correct spot. If you don't put it back the way it was, it will never start. Make sure you didn't forget to plug things back together... easy to 180 something.
 
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XxXskidooXxX

New member
Yes I have spark. We did hone the cylinders, gas is maybe 1 month old. Worked with two guys thats know quite a bit about sleds..so I'm prettt sure it was put back together correctly.
 
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xcsp01

New member
Did the motor lock up hard? Only way the timing could be off is it the crank has twisted. Or if you have the plug wires switched around.
 
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jimfsr

New member
plugs fire at the same time, not the problem. put staring fluid down the plug holes and try it. Sometimes for whatever reason thats all it takes the first time. Then they fire right up w/o a problem. The after rebuild compression seems low though, if the cyl walls were lubed at assembly, it should be 125 or so, but could just be the guage. If it runs on starting fluid but not carbs, then you know its a fuel delivery problem. Also, make sure the carbs are in the correct location, the mag side has a larger main jet and both should have colored dots (blue pink) to correspond w/ the dots on the intake boots.
 
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XxXskidooXxX

New member
We didn't even have to remove the carbs on this sled. We did try Starting Fluid but still no pop. What would cause the crank to twist? (like xcsp01 said)
 
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xcsp01

New member
I don't know how your plug setup is but on my xcr motor with separate coils you it wouldn't run if you had a plug wire switched. Hard motor lock ups, flooded bottom end can twist (turn/phase) a crank.
 
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anonomoose

New member
If you have spark as you say, and you shot some starting fluid in the plug holes, and still no short run, then the ONLY thing this can be is no compression at the time of the spark. Try switching the plug wires, and be sure you have new plugs in it. It is possible you have a weak spark where you get a spark outside the cylinder, but not under compression.
 
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XxXskidooXxX

New member
I switched the plug wires..nothin. Brand new spark plugs. The snowmobile IS receiving gas because the plugs are wet when we pull them out.
 
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rmk4ever

New member
Check reeds & crank seals, both are plastic... Both will melt under high heat. Spray starting fluid around clutch side seal & mag side see if she starts. If you melted the rings to the piston that's in the neighborhood of 1400*
 
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motor_slut

New member
My guess is the bottom end filled with coolant when you pulled the motor apart. Here's how to fix that: pull the spark plugs and hold the throttle wide open while pulling the starter rope. If there's excessive liquids coming out keep pulling until it stops. Then give the spark plugs a good heating with a torch to burn all of the gas/coolant off of them and reinstall. Once you have the plugs in and connected give it a few pulls and see if it will start. If it doesn't repeat the process until it does.

You should have drained the bottom end before putting the new pistons in.
 
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snowfreak56

Member
motor_slut said:
My guess is the bottom end filled with coolant when you pulled the motor apart. Here's how to fix that: pull the spark plugs and hold the throttle wide open while pulling the starter rope. If there's excessive liquids coming out keep pulling until it stops. Then give the spark plugs a good heating with a torch to burn all of the gas/coolant off of them and reinstall. Once you have the plugs in and connected give it a few pulls and see if it will start. If it doesn't repeat the process until it does.

You should have drained the bottom end before putting the new pistons in.
Click to expand...

X2 and stop shooting either down the plug holes you are washing down and drying out the pistons rings and cylinder walls that is not a good plan.Try a couple new plugs also.some will argu this but if you are useing old plugs i have seen either kill them.If you have spark,fuel and compression it should start unless it is way out of time.
 
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