61" cylinder bore

[myers1960]

I recently aquired an "E" model knucklehead motor which has been in storage for 30 + years.The motor was rebuilt 30 years ago and never put into service. I removed the heads to do a rough check and visual on the bore and check the piston markings. The pistons were marked .010.
I rough checked the bore at the top of the cylinders with a set of verniers and got a measurement of 3.4475. Since this was .010 over what would be a "74" bore I checked the stroke. The stroke measurement supported the fact that they were "61" wheels. In Palmer's it's stated that the castings for "5 fin " cylinders were the same for both "61" and "74" knuckleheads. The "61" cylinders have a lip at the top, though, which are present in this motors cylinders. This bore measurement would suggest then that the standard "61" bore of 3.3125 has been opened to .130+ over standard. Do these cylinders have the capacity to be bored up to .070 over a standard bore for a "74" motor? Are they safe to run at the size they are? The casting #'s match the vin of the motor and all fins are intact. Was this common practice 30 years ago?

[Cotten]

I ran my own '37 castings at .125" over for many years (until a bluehair took me down from behind), and I still have a customer's 7-fin cylinders in active service at .155" overbore.

They both operated delightfully without overheating or excessive noise.

The mandatory "trick" is to finish-hone the last full .003" while installed in torque-plates.

For reassurance, it is logical to measure your remaining wall at the thinnest spot: directly over each basenut flange. I have complete confidence in .070" remaining wall if properly fitted with plates.

You have nothing to fear but fear itself. Or lack of attention to detail I guess.

[Cotten]

Doh!

I guess I should have read "announcements" first, but that last post was mine:

...Cotten

[myers1960]

Thankyou, Cotten. I appreciate you taking your time to respond.