Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Milling heads

Milling heads

Moderators: Curt!, Pa

Post Mon Feb 20, 2012 9:55 pm

Posts: 536
Location: Wa, USA
I spent the day today milling, grinding, CCing heads, and checking valve clearance. I have the heads down to 2CCs difference (114 and 116). The valve clearances are FI: .150; FE: .090; RI:.175; RE: .090. The head with the larger chamber has the lower Intake clearance. I am leaning toward leaving well enough alone and not messing with them any more.

Comments, ideas, opinions, please.

Post Tue Feb 21, 2012 3:57 pm

Posts: 150
Location: Carver, MN

A couple of thought for you. On an 80 inch flathead the difference of 2cc would be about .09 of a point of compression. In other words, using raw head volume numbers uncorrected for piston deck height, gaskets and such, 116cc would give you 6.62:1 C.R. while 114 would give you 6.71:1 C.R. (That is NOT your actual C.R. - just an example)

Another thing I'll just throw out there: On late model Harleys, both Twin Cam and Evo, I have more than once measured a +/- of 1cc difference on new factory heads. So if you are within 2cc, then you are doing as well as the factory castings are today.

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