Old 10-30-2020, 02:35 AM
1QwkSport2.5r's Avatar
Join Date: Oct 2006
Location: Cottage Grove, MN
Posts: 9,942
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Some engines need the head shim for proper head clearance. Some engines have negative head spacing without the shim which causes the piston to hit the head. Also to note - the shim isn’t there to seal the head; it’s there to provide clearance from the piston. So D3MON is right - it’s technically not necessary for some engines. I would measure the head clearance to see how much clearance there is (it any). If you have at least .4mm (.015”) head clearance or more, then run it without the shim. If you have less clearance than that, put the shim back in. You can cut your own shim from shim stock available from K&S Hobby if that is easier to get than the factory shim (which is usually too thick anyway).