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Discussion Starter · #1 ·
K, so last year at the end of the winter i blew one of my piston skirts, being a cheap 17 year old i just put new pistons and gaskets in. So now about 250 miles later im starting to see some of the symptoms before it went last time again. And im sure the clearence is way to high. So i want to ride this thing and fix it right so off to the local sled parts store i go and get 2 new renaskiled pots, new pistons and gaskets and before i install them i want to ensure they will work good. i checked the cleasences and what concerns me is that the piston has about .020'' of movement at the top but about .0035 at the piston base. i like the .0035 but the .020 scares me, any opinions?

Oh and there spx pistons
 

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Discussion Starter · #3 ·
Im just wondering about the clearences and why there are such differences, id actually measure the pistons if i had a micrometer but dont, and the manual doesnt show how to check the cleasences at all just gives specs
 

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the top of the piston doesnt expand as much as the skirt does so naturaly the mesurements are going to be a little off and they do have a slight taper to them when they are made, its all in the design. and those clearences sound ok for any normal trail sled, if it were more racing i would say no...
 

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Discussion Starter · #5 ·
But if the top doesnt expand as much why wouldnt it have close tollerances and the base have the larger. It concerns me because i can actually wiggle the piston when its in the cylinder, to the point where its very audible
 

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If you don't have the tools to properly measure stuff, then get them. They are considerably cheaper than another rebuild, and you'll have them for later use.
 

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Discussion Starter · #7 ·
Ugly_old_Poo_kid said:
If you don't have the tools to properly measure stuff, then get them. They are considerably cheaper than another rebuild, and you'll have them for later use.
Im going back the the store tommorow, im sure the cylinder is good but i know the pistons arnt, and i cant stand that, probably go and either get some wisecos or oems.
 

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classicfanatic said:
the top of the piston doesnt expand as much as the skirt does so naturaly the mesurements are going to be a little off and they do have a slight taper to them when they are made, its all in the design. and those clearences sound ok for any normal trail sled, if it were more racing i would say no...
please dont post reply to tech questions.

the top of the piston expands a whole hell of a lot more. that is exactly why the top of the piston is smaller as the op has noticed. piston are not round and are not the same diameter from bottom to top. .020(your guess) may not be that far off but no piston manufacturer or OEM supply top of piston clearance measurements. its always taken off the largest part of the piston which is near the bottom of the skirt. yous say .0035 but then you say you dont have tools to measure this? that siad i have seen some cheap taiwanese pistons that had way to much piston taper. you said these are not OEM or wiseco so that could be a concern.
you need correct tools to make these measurements but if the parts were supplied by a competent shop with fresh nikasil cylinders likely they are fine. its not worth it for you to purchase the needed tools which are expensive at your age unless your really into this maybe want a job like this some day or just like cool tools. at 17 i would spend it$$ on girls.
 
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