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post #1 of 2 (permalink) Old 04-18-2019, 03:56 PM Thread Starter
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SPI Piston Specs

Im rebuilding a 1998 Polaris XLT SP 600 due to low compression. Help me here guys, According to Polaris my end gap installed on OEM pistons are .008-.020 and average between all 3 cylinders was > .036 on top ring and >.026 on bottom rings. The compression on all 3 cylinders was 65 psi. The pistons show blow by and deep grooves on skirt and above rings which to me say either not enough lubtrication or to rich and washing out cylinders. Now I ran into a good deal on SPI pistons and sent them to machine shop to have cylinders bored .020 over but there was not a spec sheet. So I called around and the good people at Hi Performance Engineering sent me a spec sheet they had found. My bore before honing is 65mm and with new pistions will be 65.50 mm and SPI state bore size of 50-65mm should have piston to cylinder of .004-.005 for liquid cooled engine and state "two ring piston end gap should range from .010 -.035".

1. The machine shop thought the .004-.005 was a bit odd for a liquid cooled and was wondering if anybody had any thought with SPI piston kit?
2. The installed end gap of .010-.035 seems broader range than original Polaris specs?
3. Can the 4 line oiler be adjusted or is it set to pump a certain amount of oil during operation?

Thanks- Shane
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post #2 of 2 (permalink) Old 05-08-2019, 11:01 AM
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You can't wash down the Cylinders in a two stroke as the oil is delivered to the engine mixed with the gasoline.

Forged Pistons need way more clearance than cast Pistons do .. so always go with Piston manufacture recommendations..

You did not say how many miles the engine has .. If the Pistons are scored.. Maybe you do need a bore Job.. Some times you can just hone the Cylinder walls and use new pistons and rings..

The newer engines don't have cast Iron sleeves than just Nicklsill plate the aluminum castings ect.

It's easy to over heat a snowmobile with lack of snow or ice hitting the heat exchanger.. proper oil proper fuel all mean nothing if you overheat it..

Also you can cold seize forged pistons.. You have to warm an engine up before you run it hard..
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