Oversized piston vs factory sized pistons???

[Canadian_bacon]

Hey all,

so I recently found the compression on my '89 Polaris longtrack to be 120/60psi.
I tore down the top end and found one piston damaged. I called the Polaris dealership and was told they don't make those parts anymore. He did say that I could bore out the cylinder and put in an oversized piston on just the ONE side which seemed strange to me. When I asked if I'd have to do the other side he said no, just the one and that it wouldn't make a difference. Can anyone confirm this? Also, how would that work cause the math to me would be inproportional per side. He claims it doesn't matter as long as I'm within 10-15%. I have my doubts and think I should just save myself from grief and do both sides but it's twice the price. Any thoughts?

 

[CatMan16]

I would bore both cylinders and put in some aftermarket pistons. Make sure you get all the debris out of bottom end before reassembling. I have a hard time believing that mixing the bore sizes wouldn't cause issues.


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[007sevens]

Hey all,

so I recently found the compression on my '89 Polaris longtrack to be 120/60psi.
I tore down the top end and found one piston damaged. I called the Polaris dealership and was told they don't make those parts anymore. He did say that I could bore out the cylinder and put in an oversized piston on just the ONE side which seemed strange to me. When I asked if I'd have to do the other side he said no, just the one and that it wouldn't make a difference. Can anyone confirm this? Also, how would that work cause the math to me would be inproportional per side. He claims it doesn't matter as long as I'm within 10-15%. I have my doubts and think I should just save myself from grief and do both sides but it's twice the price. Any thoughts?

Im sure you can find a aftermarket direct replacement

 

[Eldereldo]

My feeling that you are asking for trouble if you only do one side. Unless you know the cause of the piston failure and that is would not have affected the other side, you are just asking to have it go,shortly after you rebuild the one side. The other thing is that you are then going to have one piston the is heavier than the other, unless you can somehow remove material from it to balance the weights. My feeling is, that once you are into an engine, fix all related parts, at the same time.

 

[Canadian_bacon]

That's kinda the way in leaning too. Any suggestions on cleaning out the crankcase without taking it apart?

 

[Clode]

Hey all,

so I recently found the compression on my '89 Polaris longtrack to be 120/60psi.
I tore down the top end and found one piston damaged. I called the Polaris dealership and was told they don't make those parts anymore. He did say that I could bore out the cylinder and put in an oversized piston on just the ONE side which seemed strange to me. When I asked if I'd have to do the other side he said no, just the one and that it wouldn't make a difference. Can anyone confirm this? Also, how would that work cause the math to me would be inproportional per side. He claims it doesn't matter as long as I'm within 10-15%. I have my doubts and think I should just save myself from grief and do both sides but it's twice the price. Any thoughts?

kimpex makes good replacement pistons for sleds like that, I used lots of them when I worked at the dealer. I would go oversize on the piston and change both sides so the piston weight is close to the same.....any dealer that would suggest mismatching pistons is questionable

 

[Clode]

That's kinda the way in leaning too. Any suggestions on cleaning out the crankcase without taking it apart?

split it, otherwise its a crapshoot

 

[rebel]

Im sure you can find a aftermarket direct replacement

X2
https://www.google.com/url?q=http:/...azKDLU&usg=AFQjCNHipxEDpdVQHdItdLeHaWi_IZ6RDw



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[DRD]

Ran lot's of older iron like that with one oversized jug, never noticed a difference. Do you want it right or right now?

 

[moyiesledhead]

Ran lot's of older iron like that with one oversized jug, never noticed a difference. Do you want it right or right now?

Same here. Did that lots with low HP engines. Never a problem.

 

[Canadian_bacon]

Ran lot's of older iron like that with one oversized jug, never noticed a difference. Do you want it right or right now?

Huh...you're the first person to suggest it will work with two different sized pistons. While I'm sure it will, I think I'm still more comfortable doing both the same. I also think I need to replace the head cause it has matching putting with the top of the piston. Thanks for you input.

 

[RapidRevolutions]

There are lots of aftermarket pistons available for that machine. I just glanced in our book (as I didn't know your exact cc's) and Wiseco has lots listed for 89s and a few other brands too. General practice in school we are taught never to run two different sizes of pistons for balancing reasons. But on an older sled the rotating mass is a lot heavier so one size difference would still work just not recommended. We can get you stock bore pistons if your cylinder is still good. Plus we can hone it for you and check it for out of round. However looking at your pictures I think you have a leaky bottom seal on the crankshaft causing a vacuum leak on the one side of the engine. Which is possibly why the one cylinder melted down and the other didn't. Happened on my 2002 Polaris 800. Let us know if you need any parts or machining I'm sure we can help you out.

 

[DRD]

Unless the head is really smashed blend the marks to get rid of high/hot spots.
As suggested find out why it went down or it will happen again


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