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Ski-Doo: ZX Sleds 99-2005, all models in the ZX chassis
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Old 11-24-2018, 05:11 AM
awsome al awsome al is offline
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Default 2000 mxz 500 rebuild question

Ok im rebuilding my 2000 mxz 500 ordered a rebuild kit off ebay put it together and left it sit till now went to start it and piston is hitting head. I did looking never knew there was different thickness of base gaskets but the highest the go is 0.8mm and my piston is sticking about 1.5mm over my cylinder right now with paper thin basr gasket. So my question is how much should my piston be sticking up on my cylinder i thought its expose to be flush with top of cylinder and if so how can i make up the room I need?
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Old 11-25-2018, 05:43 AM
Rick E Rick E is offline
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Quote:
Originally Posted by awsome al View Post
Ok im rebuilding my 2000 mxz 500 ordered a rebuild kit off ebay put it together and left it sit till now went to start it and piston is hitting head. I did looking never knew there was different thickness of base gaskets but the highest they go is 0.8mm and my piston is sticking about 1.5mm over my cylinder right now with paper thin basr gasket. So my question is how much should my piston be sticking up on my cylinder i thought its expose to be flush with top of cylinder and if so how can i make up the room I need?

I don't know the precise answer for your Bombardier engine........, but I'll share what I know about other 2-stroke engines and the SBC in both Auto and Marine.

Pistons and connecting rods will grow in length at high RPM.
So when we build an engine, this must be accounted for in order to avoid piston/head contact.
The depth at which the piston sits in it's bore is referred to as "piston deck height"!
The distance from the cylinder block "deck" to the cylinder head surface is determined by the compressed head gasket thickness..... or in the case of the Rotax 2-stroke engine, this will be the compressed gasket thickness underneath the cylinders.
This determines not only the clearance, but also the quench/squish dimension....... (but you will not need to be too concerned with that on this engine! Just pay attention to the correct deck height!)

As you mentioned, Bombardier Rotax Engine rebuild kits should provide an array of base gasket thicknesses as to raise/lower the cylinders in order to acquire the proper piston deck height.
Because of the high RPM piston/rod stretch, the piston (@ TDC) will ideally sit a few thousandths below the deck.... aka "in the hole".
You can find formulas that will help you determine this dimension..... but I would suggest using what Bombardier recommends.

There are several knowledgeable members here, and I'm sure that one of them can direct you to a spec sheet.
Since this dimension is very critical, I would prefer to see an OEM spec on this!

I'm glad to see that you caught this early on!
Had the pistons NOT contacted the cylinder head during your assembly, they may have later on dynamically...... and what a shame that would have been!

Good luck, and post back with your findings!

Rick E.


Last edited by Rick E; 11-25-2018 at 08:32 AM.
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Old 12-03-2018, 12:31 PM
BBP BBP is offline
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There's more than 1 500 engine. You probably have the wrong rebuild kit. I highly recommend that you verify what you have, as installing the wrong pistons will more than likely destroy your engine.
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