We had to do a combustion chamber repair on some CNC machined LS3 cylinder heads that dropped an intake seat. We wanted it to perfectly match the other CNC chambers. After the new seats were installed and the valve job was cut to the proper height, we popped in a couple valves and a spark plug that had the electrode removed to seal the holes. We sprayed the chamber with liquid silicon spray as a release agent and then filled a good combustion chamber with body filler. To make it a little easier to hold, I stuck a bolt in the filler before it hardened to act as a handle. Now, as I’m grinding and reshaping the newly welded up chamber, I can use the mold to test fit and will end up with the exact same shape and volume when it’s done. If you can’t quite tell where its tight towards the end of the job, you can use dye-chem or Prussian blue in the chamber and rub the mold against it to leave a witness mark. Leave the valves out of the chamber you are reshaping so that if there is a slight difference in seat height it won’t interfere with the fit of the mold.

Jake Sampson
Sampson Race Engines
Inver Grove Heights, MN
April, 2019