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Discussion Starter #1
Did a top end rebuild on the sled with SPI pistons/rings/piston pins and a full winderoa gasket set last year and came back to the project recently as i ran out of snow last year. i split the crankcase and found the crank was out of spec but had it trued. Sealed crank with RTV. Also put thin layer of RTV between base gasket and crank. The jugs were honed and are spotless. I did notice that the pistons had small scratches on them but they seem to have a coating to them. Ring gap and piston to cylinder wall is in spec Its having hard starting issues. compression is 100 pto and 105 mag side. This is my 1st rebuild but have taken a couple of motor night courses through a college. Will this compression go up as the rings break in or am i missing something. I've already eliminated a vacuum leak by doing a leak down test and it held. I've gotten it to run but the only way is to put your hand in the intake of the carb to increase the vaccum going to the carb. So is this compression too low for the sled to start on its own or i missing something here?

Thanks, Skyler
 

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We may all be missing something here. I put a used piston and new cylinder on the pto side of a 440 F/C last year and had 120 compression on both sides
 

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Discussion Starter #3
Did you reuse the oem gaskets and rings or did you replace them with aftermaket ones. I'm suspecting these base gaskets are already on they way out or the fact that I put rtv underneath the base gasket as I've already found peices of it on the piston as the jug has been in and out a couple times already
 

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I had a gasket kit here so I replaced them on the cylinder. I used the rings that were on a factory piston bought used on ebay
Since you had the crank out, did you replace the seals on it?
 

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Don't know if this is your particular problem but RTV silicone will not tolerate gas which your crankcase and base gaskets see.
 
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