Clutch Hubs

Production K Models

Clutch Hubs

Postby John R » Tue Apr 22, 2014 9:13 pm

First of all, a big thank you to Dave Hennessy for creating this site and all the other experts feeding it. It's going to be great!

A riveting story, and it starts when I bought a '56 KHK ripe for rebuild. The clutch had a lot of shake in it (1/8") so with an unbalanced off-centre clutch it must create vibration, which also helps wear out bearings, etc. This shake is the total of the clearances in the mainshaft ball bearing and the thrust washer in the clutch-hub. The latter is supposed to be 1 to 4 thou - I had 16 thou.

The later '57-up clutch-body and hub was fitted which has 12 rivets retaining the assembly. I ordered the parts needed and set-to. To my surprise the old rivets were 5/32" in a 3/16" hole, but that's what the parts book says - 8215 rivets 5/32" x 3/4". I'm used to Harley rivets being serious interference fits, not these! Anyway, as it was all 'by the book' I finished the job. The KHK is great, so worth all the effort of a total rebuild.

Now the plot thickens. My '53 KK (which I've owned for 14 years) broke a shifter return spring which is a complete engine / transmission strip, so worth freshening everything up, including the clutch-hub for the same reason. This one is the original early type with 6 rivets and non-brazed (removable) clutch hub. On de-riveting the rivets were 3/6" diameter with solid interference fit.

The earliest parts book I have is '54 which lists 8215 5/32" rivets, but I suspect early Ks used 3/16", but why the change? Anybody out there with an earlier parts listing?

My theory is that Harley over-engineered the design creating a manufacturing headache. The early clutch needed three components all precision drilled with 6 holes to line-up perfectly. With interference fit rivets, just a 1 thou tolerance in positioning would be the limit.

The clutch-hub itself (needle bearing carrier) has all 6 holes at 1 thou under 3/16". To ease matters, H-D had just 1 hole in the clutch-body at 3/16" dead, the other 5 holes are +2 thou. The starter-clutch (ratchet) on the other side of the assembly has all 6 holes 3/16" + 2 thou. Even then it's a selective fit with the 6 holes in all 3 components aligning best in one position only, and it's not perfect even then.

But I thought, just 6 rivets, better use 3/16" as original and ordered NOS 8243 (used on front cush-drive). New problem! These rivets are nominal 3/16" but are tapered from -1 thou to +4 thou. No way would they fit! Now I need some 3/16" parallel and I can finish the job.

All this leads me to think that Harley decided that it was all too much production headache and went with 5/32" rivets, but doubled the number to 12 to take the torque of the starter-clutch - it was no longer a solid riveted job, but a clearance job which might shear with only 6 rivets.

Photo below shows the stripped assembly. The taper rivet sits much higher in the 3/16" dead hole in the clutch body. The left rivet in the starter-clutch is one of the original rivets and is a light press fit - the right one is a taper rivet. On the extreme right is a 8215 5/32" rivet out of the '57 assembly.

Any input welcomed!
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John R
 
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Re: Clutch Hubs

Postby dr dick » Mon May 26, 2014 9:30 pm

one theory that has been kicking around is in the removable bearing carrier drums used the rivets as pins to keep fretting at bay.
the later drums with the sweat brazed carrier didnt need this?
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