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Mart · 09-14-2023, 02:33 AM

If your pistons are lifting the heads .020", things are pretty tight. Sure it's not the valves?

Some pistons have a "pointy" dome. not a true dome. The heads can sometimes have a true dome. This is the situation in french pistons for instance.

When I had this problem I filed the heads of the pistons in the middle to reduce the pointiness. If you assemble the head on with the gasket dry you ought to be able to use it again after checks.

I wouldn't go full torque though, 20 or 25 lbs ft would be enough to check for clearance.

Bear in mind you want 40 to 50 thou clearance, those final few thou when going to full torque can be borne in mind.

I use aluminium foil crumpled into balls held in place with grease (vaseline) when checking clearance. All around the piston and on the dome.

Bear in mind I am not an engine builder. Others may have other methods that they prefer.

I am surprised the pistons are lifting the heads, though. Have the heads been heavily skimmed?

Hope any of this helps.

Mart.

09-14-2023, 02:33 AM	#80
Mart Senior Member Join Date: May 2010 Location: Solihull, England. Posts: 9,240	Re: Rebuilding my Flathead random questions If your pistons are lifting the heads .020", things are pretty tight. Sure it's not the valves? Some pistons have a "pointy" dome. not a true dome. The heads can sometimes have a true dome. This is the situation in french pistons for instance. When I had this problem I filed the heads of the pistons in the middle to reduce the pointiness. If you assemble the head on with the gasket dry you ought to be able to use it again after checks. I wouldn't go full torque though, 20 or 25 lbs ft would be enough to check for clearance. Bear in mind you want 40 to 50 thou clearance, those final few thou when going to full torque can be borne in mind. I use aluminium foil crumpled into balls held in place with grease (vaseline) when checking clearance. All around the piston and on the dome. Bear in mind I am not an engine builder. Others may have other methods that they prefer. I am surprised the pistons are lifting the heads, though. Have the heads been heavily skimmed? Hope any of this helps. Mart.