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Discussion Starter #1
I am about to buy a 1994 ski-doo Mach Z 780 one of the pistons is blown what i need to know is how to change it out any tips or advice?
 

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pull the head
pull the cyl with the bummed piston
check cyl damage
if damage you will need to over size boar and get a bigger piston
No cyl damage
replace piston
get torque specs
 

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Dont drop the needle bearings. Im not sure if they are caged on that model but Im sure they are not.
 

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get somebody to rebuild your engine, not to be rude, but these are vital parts and specs for your top end, and if you didn't know what you are doing then a $300 dollar rebuild can turn into a $3000 bill, get someone to help you out and learn
 

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Discussion Starter #9
I replaced the piston and found out what needle bearings are and what a pain but i got them all in now can u find torque specs anywhere online? because i dont have the manual and i dont want to go all the way to the dealer just for that thanks
 

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Just give your dealer a call and tell him your year and model and he should be able to give you tourque specs, ask for the tourque specs for everything on the motor and write them down as he tells you. Keep them in a folder or somethin for next time u gotta dig into the motor.

Good luck.
 

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Discussion Starter #11
ok heads on plugs are in its ready to go right? or not i filled it up with oil, antifeeze and gas it the start cord pulls extremely hard and the antifreeze i put in came rite out through the plugs and bottom of the right cylinder whats wrong?????
 

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????????????????????????
You have a major problem, or you didn't put the engine back together properly

BUY A SHOP MANUAL

I got one from Ebay for $12 on my door step
 

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did you follow all the procedures? Seriously, you have to check the cylinder bore for damage and wear, you have to hone the cylinders for the rings to seat, the rings have to be aligned on the pin in the piston, the piston has to face the right way, the rings sometimes have to be filed sown for optimal fit, etc etc etc....this is why its almost always more feasible to bring it to the shop....
 

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Discussion Starter #16
yes im sure i put in the piston right im replacing those circle seals on the cylinder now im hoping that will take care of the anti freeze problem but i dont think there should be that much oil in that one cylinder could it be jets?
 

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I'm going to have to agree you need help from someone, try a dealer or a friend that has some knowledge in this area. Did you connect the oil line correctly, there shouldn't be that much oil sitting in the motor.
 

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Discussion Starter #18
ok i got it running, but poorly it wont idle it dies if u dont have your hand on the gas. and i still have the problem with anti freeze leaking out of the plug holes whats going on?
 

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Sound like the problems you are having are related. Coolant doesn't burn very well. I don't really know ski-doo's that well, but it sounds like your gaskets are installed incorrectly, cracked head, or a crack in the water jacket some where.
 
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