Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Milling crankcase deck surface – How much?

Milling crankcase deck surface – How much?

Moderators: Curt!, Pa

Posts: 83
How much metal can be cut off from a stock UL crankcase deck surface without having a major manifold alignment problem. I’m trying to set the squish at 0.045-0.05 but I don’t want to mill the top of the cylinders, because both cylinders had already been nicely relieved and polished. Any suggestions?

Posts: 2677
Location: Los Angeles, CA
Mill the base of the cylinders.

Posts: 83
Thanks for the reply. But my dilemma still remains unsolved. As far as I know, milling the base of the cylinder will also affect the manifold alignment in the same extent. In order to reach 0.045 squish I must cut off 0.05 (crankcase deck or cylinder base). If I do so, will I need a custom manifold?


No, most manifolds are slightly loose, and the relationship isn't linear.
At worst you just file the ends of the legs slightly.

Posts: 83
Thanks Panic! and Chris!
Helsingborg. :mrgreen:

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