Polaris 800 Fix Kits

[RK Tek]

If using a fix kit the cylinders are raised up off the bottom end of the engine so that the pistons can be made taller which in turn makes the piston more stable inside the cylinder. It is much less likely to slap/rock compared to the shorter stock piston.

As far a clearances go. Most aftermarket pistons seem to be forged. A forged piston will expand more when heated than a cast piston. Forged pistons should have more clearance do to the higher expansion when hot. Not so good for cold startup. They will also less dimensionaly stable when the engine is running as the temp of the piston changes according to engine loads.

A hypreutectic cast piston changes dimension much less than a forged piston and remain in tighter spec over varying engine loads. This mean less wear over time. Much less wear on cold startup.

A forged piston is stronger and good for very high stress engines but lower longevity is the the trade off.

I suspect most stock oem pistons may not be forged as they generally offer the best longevity. This may not be the case in these 800 engines though and could account for the shorter life of the pistons and cylinders.

"performance or upgrade" pistons are not always a good thing from my standpoint.

2008 Polaris Dragon 800 163"

I understand that is a "common" belief that the forged pistons require more clearance. BUT... it is not always the case and not always true. You can run a forged piston at cast piston clearances without having anymore risk of failure and you gain the benefits that come with a forged piston as a result.

As for a raised cylinder adding more support.. again.. common belief but not always true.

When you raise the cylinder you also raise the lower cylinder skirt which is what the piston thrusts against when changing direction at BDC and where the issues lie in terms of cylinder (or lack of) support on the Polaris CFI 800 engine.

Raising the cylinder REMOVES/Lessens cylinder support for the piston to thrust against around BDC.

Near or around TDC, the piston is fully supported by the cylinder but not at or around BDC. Now, it is true that some of these "Fix Kits" are a taller piston than the OEM piston, BUT they are only taller from the wrist pin to the crown edge.

The Lower piston skirt (the one that collapses and fails) is the EXACT same length as the OEM piston AND you have removed some of the cylinder support because of the shim.

Not saying any of these kits are bad and do not perform better than the OEM piston. Just stating some geometric differences. It is not hard to better the OEM piston. IMO it is a poorly designed piston that should be replaced