Flywheel Crankpin Key Question

[BigLakeBob]

Can someone educate me on why a BT OHV (maybe BT SV too?) has the crankpin key on the right flywheel and a 45" SV has the crankpin key on the left flywheel? I would think the right would make more sense to ensue line up of the oil feed hole. I know the wheel shouldn't be rotated enough to matter, just curious as to why the difference.

And a follow up question. It seems like HD OEM nut to shaft fits (concerning flywheels) are very tight, (not a hand assembly). I compare a new 'Jim's' shaft and a new Colony nut and the assembly is a fit like (me being a machinist) would fabricate. Sometimes the Colony nuts are too tight on an OEM shaft, same as oem nut to shaft fit. Is the opinion that HD made their shaft threads on the larger side of the pitch diameter for a very tight fit or this just happened through production tolerances? I just hate threading a nut on with a wrench from the get go. Opinions?

Thanks.

[exeric]

From my limited experience; I would want the nut to fit precisely (not tight, not loose) on a crank pin, sprocket shaft, and pinion shaft. H-D provided retainers to keep the nuts in place. Excelsior made (one side) interference nut to axel shaft fits which worked well for the rear wheel application, and also on motor mounting bolts. Again, I wouldn't like tight fitting nuts along with all the other aggravations of assembling, and truing flywheels.

[BigLakeBob]

Alright, forget the crankpin question, a mystery, I guess. How about the nut to pin fit. Alot of you guys have built engines, any opinions? Just opened an OEM NOS HD 45" crank pin with factory nuts from 82 years ago. Threads are 'buggered' and nuts only thread on 1/4 turn. Checking threads using pin gages and going with industry standards, HD's threads seem to be large making it an interference fit. Is this what all you engine builders did, just crank the nut down over the large threads? Is this what HD intended for a fit that wouldn't loosen? Thanks. 20251203_195010.jpg 20251203_195032.jpg 20251203_195114.jpg

[Rubone]

That is pretty normal on them Bob. The copper plating was done after the threads were cut but before hardening and final grinding of the bearing surface. The threads tend to be oversize.

[BigLakeBob]

Thanks for the response Robbie. I decided to deburr the damaged thread area, only makes sense. I also made a split nut to lap the threads for a 'softer' fit. There is torque on the threads before even seating the nut on the flywheel. Not trying to redesign HD's remarkable engine durability, but I think a tight no shake thread fit is ideal. Do the engine builders here agree or disagree? Thanks.

[dukekleman]

Bob,

The idea behind copper coated threads creating an interference fit was the early technology of filling air gapping with a soft forming material. All while conforming with similar and dis similar metals (active and inactive).

As we know thread contact surface area can be as low as 15% when torque is applied to new components.
Cooper used as a filler in many applications, when used in this application, can shift and form itself into unwanted air gaps in the thread pitch, hence creating a greater mechanical bond.

The frequency created in a flywheel assembly from combustion and reciprocating parts causes a loosening affect. Copper coated threads and torque are first in line of defense against loosening. The lock plate is very minimal and very inefficient by comparison.
Today, Loctite is used in place of both the copper plating and lock tab plate and screw. It is very effective!

Of course torque application all needs to be developed and tested in both scenarios. Cooper causing resistance and loctite reducing resistance while in liquid state.

I hope this helps,

Duke Kleman

[T. Cotten]

Gosh, Duke,

I was assured the copper dip was just part of the heat-treat.

....Cotten

[duffeycycles]

I agree with Duke & I don't lap them.

[DEEBS47Chief1991]

Sort of an early form of Loctite.

[chuckthebeatertruck]

I never have heard of copper plating being used to fill threads . . . and I'm pretty well versed in ancient industrial applications.

I have heard of copper on threading to prevent heat treatment distortion . . .

I'd be curious if there is literature on this one.

I'd also be curious why I've never seen copper plating used this way on any other crankpin I've ever worked on.

Not flaming -- asking a real question.

[BigLakeBob]

I talked to two long time (one 45 yrs and other 65 yrs of experience, yes they are older ) HD mechanic friends of mine about the nut to shaft fit issue. They both said they encountered this problem all the time and had a bin full of nuts and match fit until the thread is good tight hand fit-not loose, but not where you need a wrench to actually apply heavy pressure to get the nut on. You may actually get pre torque before you get the nut seated. They both have had to lap the nuts to the threads and both feel the copper was only for heat treat purposes. I actually feel that if the threads are lapped for a good tight fit you will have much better contact with very minimal 'air gap' contact surfaces. I've decided to fit tight but without forcing the nut on the copper coated soft threads which could cause a galling. I appreciate the conversation and input from everyone. This is alot more fun than welding the crank pins to flywheels like modern HD's do! IMO