700 mm piston tightness in cylinder question

ebayfreak

ebayfreak

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Joined
Feb 17, 2007
Messages
195
Age
54
Location
newfoundland, Canada
doing on a rebuild on my mountain max after a meltdown on clutch side. Got all cylinders and pistons installed but the mag side piston was a bitch to get in the wall. the other two pistons have some movement when you push on them but this one doesn't . By being tight in the wall will this affect anything, i've swapped rings and still the same. it's got me dumbfounded as this was the cylinder that never melted and had 125 psi when i pulled it apart.all parts are yamaha oem. Any info would help guys!thanks!
 
If the piston is tight in the bore you WILL have problems. Swap one of the other pistons into that cylinder to see if the problem is with the piston or the cylinder. Try it with or without rings as well.
 
take a micro meter and mic the pistons and mic the walls and see if anything stands out..to tight of a piston will expand and seize that cylinder .
 
i checked piston and cylinder and they seem within spec, the piston moves up and down in cylinder smoothly but the side to side play on top is much tighter than the other two. i'm thinking that maybe the other two have more wear. I guess i check the other two as well and compare. thanks for the info guys!
 
i put a used piston in the side that melted, the piston that is tighter is one of the originals. I bought this and never got a sensible ride on it. it was on the way out and i got burn't. now i'm fixing somebody elses quick fix. pistons and walls are in good shape now, just the mag side has less movement than the other two. I'm putting it in the machine today with my fingers crossed . this winter has been hard on the pocket and i've spent more time in the garage than on the snow. hopefully later the week will have a trial run. will let you know how it turns out.
:o| :o| :o| :o|
 
Your last post gives a better picture of whats you are dealing with.
There is no way to accurately check your piston clearance by feel. Since you are dealing with all used parts, both cylinders and pistons, the clearances would likely all vary.
As you probably know, if you've ellected only to use your used parts, the pistons and cylinders should all be mic'd for size and then you can match the parts for the best clearances with the parts you are dealing with.
Good luck on rebuild...too bad you got stuck with someone elses issues on your sled.
 
Is it really worth the chance to replace with used parts if you already don't feel confident they will work? If it blows it will probably cost you more than it would had you waited till you had the $ to replace all the pistons and rings. These are just my thoughts. Good luck
 
i would if i had the money, but i just finished rebuilding my srx that costed a fortune.yamaha parts are expensive here and take so long to get from dealer and our snow is starting to go. I replaced the piston and cylinder from a machine with low miles and they were in spec.i've seen these 700mm tortured here and still not blow. i'll need the luck lol!



sockeyerun said:
Is it really worth the chance to replace with used parts if you already don't feel confident they will work? If it blows it will probably cost you more than it would had you waited till you had the $ to replace all the pistons and rings. These are just my thoughts. Good luck
Click to expand...
 
it's alive ....finally :)

the beast is alive after months of dealing with gremlins. turns out to be a faulty piston. the rings wouldn't fit into the grooves properly and just jammed into grooves.piston was one of the originals too go figure. 125+ psi across the board now. Too bad our powder is gone but i'm hoping to put a few miles on in the mountains before storage, thanks guys for the help! ;)!
 
usually compression with new rings takes some time.,normally you will have around 120 or a little less,as they break in they will hit 125.Mine after 2 seasons on rebuild am getting around the 125 mark now.
 
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