If an engine does not have an engine shim or a rear plate gasket, will this lead to reduced compression? Simply, I purchased an engine off of ebay and these parts were not included once received. My initial thought was to purchase a new piston and sleeve, however, I took the engine apart and noticed the missing parts. Any information would be appreciated.

Thanks.

You have to have a head shim, as for the backplate gasket not being there that would cause a major leak as well as compression loss, you can use clear silicon to seal up the backplate or see if you can buy a real gasket, i would hold off on the rebuild till you get the other problems fixed and test the engine.

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Diffrent size sims will give u diffrent amounts of commpression. For instance, a thinner sim will give you more compression, becasue you decreas the head clearance. An a thicker sim will increase the head clearance, wich will reduce the compression. Dont go to thin tho becasue you can blow up you motor. Check you manual for limitations.