Board index Flathead Power-Technical Questions, Answers, and Suggestions General Whatever-Technical 1924 to 1929 Harley J 61" cylinder

1924 to 1929 Harley J 61" cylinder

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Post Wed Sep 21, 2011 5:23 pm

Posts: 607
Location: Menomonie, Wisconsin, USA
How far oversized can a late J 61" cylinder be bored and where can pistons be gotten?


Post Thu Sep 22, 2011 7:30 am

Posts: 3158
Location: Central Illinois, USA

I have no experience with J's, but you would do well to measure the remaining casting at the thinnest spots, over each basenut flange:

Measuring is easy with a common "pincer" caliper that has had the top spring removed, and the adjusting screw reversed. Thus the tips can be opened to go around the flange, closed and carefully set with the screw, and re-opened so that the gap can be measured with feeler gauges.
Searching for the very thinnest spot is what takes the most patience, as all four basenut reliefs must be inspected.

With later cylinders such as ULH's, I have found .070" remaining wall at the thinnest spots to be safe.
It is manditory, however, that the cylinder be bored a full .003" undersize of the piston, and then torqued to a stressplate as if installed for the final hone-fitting.

Once you know your bore, compression height, etc., you might want to try Egge Machine, even if only to determine other machines that used similar pistons.

Good luck!

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Post Mon Sep 26, 2011 10:41 pm

Posts: 2688
Location: Los Angeles, CA
I once bought a J engine that had domed Knucklehead pistons in it.

Post Tue Sep 27, 2011 8:44 am

Posts: 1029
Location: Ojo Caliente,NM,USA
I still prefer the jugs bolted to the case they are going to run on for honeing. I know how straight I can make a torque plate but I also know how straight 60-80 year old cases are. If you are going to reface the cylinder mounting pad by all means use a torque plate it's easier. But whoever refaces the cylinder mounting pad on cases that look like they will seal.

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