45" Cylinder oversize options

[dukekleman]

I have a 1947 HD WL 45" motorcycle in my shop that a customer bought at an Auction. He bought it being told it had a full restoration done. The odometer reads 253 on the restoration.
It turns out it has issues throughout the motorcycle.
One of them is the engine...Upon removing the heads and cylinders it was obvious it had new pistons. They are 0.080" oversized. The cylinder bore and hone service performed is an issue and needs corrections made.

Into my question. Ted's cycle V twin offers a maximum piston over size of 0.080" , which this is already.
I see that 45 Restoration makes a 0.090" and a 0.100" over size .
I'm not sure how I feel about these? I do not have any experience with these particular oversized dimensions either.

Can any share experiences with going this big on an oversized bore. Time spent accumulating miles on an 45" motor with .090 or .100 oversized pistons in it?

Thank you,

Duke Kleman

[T. Cotten]

Huge overbores can work fine, Duke!

(They don't even have to match, and stronger than a sleeve, when performed correctly...)

You will need a base torque plate at very least.

The fastener stress distortion is maximized next to each base stud;

distort.jpg

So they should be inspected while stressed; You may even want to measure the remaining wall thickness next to the base studs, as shown upon this 741 cylinder,

THINBORE.jpg

To avoid hitting daylight!

PERFDCYL.jpg


....Cotten

[dukekleman]

Cotten,

Thank you for the reply.
Yes, torque plates are essential. I have them all the way up to M8 (Milwaukee Eight series engines) that I machine cylinders for. Some of mine are designed and made by me while the others are purchased from Harley Davidson, Jim's USA.

Ironically Early model torque plates I built myself and the latest M8 model torque plates are also built by myself.
When Harley Davidson was getting ready to release the M8 engine series I held a private conversation regarding oversized piston availability for the new engine seeing how thick the liners were. The decision was made that no oversized pistons would be available. Standard only and the purchase of a new cylinder. For reasons stated in that particular conversation.

My concern is the thickness down around the cylinder base studs as you mentioned...

So my question is:
Is there a determined wall thickness number, that I can use as a guide, with any kind of track record/experience you feel very comfortable with on a 45" HD Flathead?

Thank you,
Duke Kleman

[T. Cotten]

So my question is:
Is there a determined wall thickness number, that I can use as a guide, with any kind of track record/experience you feel very comfortable with on a 45" HD Flathead?

Thank you,
Duke Kleman

Of course not, Duke!

Factories prudently always used 'idiot clearances', not only to cover their behind with the general public, but to avoid training and outfitting their dealerships, only to extend machine's lifetimes, when they would rather sell another machine.
That's why afterrmarket offerings could exceed factory catalogs.

I can only offer anecdotes of personal experience;
Note the last pic I posted was of an aftermarket Pan cylinder of moderate overbore (memory fails so I must measure it again) that was running without perforation.
Inspection with my fingernail effortlessly broke out a rice grain piece of the cylinder wall. Note also that it is below the rings, in a region of minimal crankcase pressures.
Although this suggests the wall could theoretically "approach zero", I enjoyed success with as little as .100" (again memory fails, it may have been less) on ULHs, etc,

45s rarely needed me, so I do not know their core-float characteristics; Sleeved flattys did cross my benches, often tragic:

Perfdcyl (2).jpg

perfdcyl 3.jpg

....Cotten
PS: I have no clue what an M8 might be, sorry..