Sportster Speedometer Drive

[billpedalino]

This project is fighting me right to the end! The tank and fenders are out to the painter and I'm disassembling the rest of the machine so that I can re-paint the frame and swing arm and attend to the minor anomalies that popped up during the initial assembly.

One of the things that I didn't do when I built the motor and transmission was install the speedometer drive, as the one I had was very worn. Back in the day, I welded up several right cases that fell victim to this very poor design and wanted this area to be right - the drive, the first gear spacing, and the ring gear. Therefore, I decided to wait to find a good drive (I eventually found two) and pre-assembled the bike in the interim.

Now the motor is back on the bench and wouldn't you know it - the damn speedometer drive appears to be slightly cross threaded, apparently from some meathead trying trying to gorilla-grip it in at some point in history with the motor in the frame. My mistake was not initially noticing the cross-thread, as visually it wasn't very noticeable. Now it screams out at me!

I removed the transmission just to make sure it wasn't a gear misalignment and notice that the drive screws in several turns and then bottoms hard with an approx. 3/8" distance to go, most likely caused by the inner machined drive shoulder hitting the inside shoulder in the case.

I believe that I can straighten this out if I had the correct tap. The thread pitch is 20 T.P.I. and measured with a vernier, the O.D. taken on the threads is 0.780".

Does anyone either have the correct trap that I might borrow or know where I might buy one?

Thanks...

[vph-d]

Bill, Can you use a thread file to clean up the threads ?
VPH-D

[motorhead1]

Check these guys Bill. And they are in NY.
https://drillsandcutters.com/3-4-20-...FdcWgQodiwQDhQ

[jim d]

Could you use another speedo drive and cut a taper on the end threads of it and then cut some grooves running with the length of it to make a thread chaser?
Jim D

[billpedalino]

Thanks for the replies.
Observing that only the first few threads on the outer side of the tapped hole are crossed and after careful measurement, I drew up a custom tap in Auto CAD that will allow me to place the tap into the transmission cavity, insert it into the hole shank-first and screw it out counterclockwise toward the outside of the case, thus using the intact inner threads to act as a guide and insuring correct (critical) alignment of the gear interface. I then found found eight companies that manufacture custom taps. So far, TAPCO, Morse, Bateswell and Western Tap expressed interest. They are reviewing my drawing now.

[billpedalino]

Bill, Can you use a thread file to clean up the threads ?
VPH-D

VPH - I initially thought of a thread file but given the limited internal depth and external clearance, I didn't think it would fit unless I take the gear case apart and remove the oil pump. I really hate taking apart a newly assembled motor. However, I was being lazy in my thinking and have now come to accept the fact that I'll probably have to do so. Given that the threads are relatively soft aluminum, the thread file is certainly worth a try especially considering that the inside threads are not damaged and offer a proper guide for the file teeth. I don't have an internal thread file so I'll probably buy one and possibly cut it down if the length is a problem. However, it's a lot less expensive than the custom tap ($165 - $225), which I still might have to buy if the file doesn't work to my satisfaction.

Whichever tool works - this must be done correctly. I must be certain that these threads are straight and that the cable drive gear meshes properly with the ring gear on counter shaft 1st. This area of these early motor cases was a real trouble spot that sometimes caused a terrible outcome.

[vph-d]

Bill,
I ordered replacement cases for my wife's 69 XLH because the originals were badly cracked thru the speedo drive/countershaft area.
VPH-D

[billpedalino]

Bill, Can you use a thread file to clean up the threads ?
VPH-D

As per your suggestion the problem is solved. I bought an internal thread file, cut it to a 3" length and carefully worked the outermost threads. It took awhile, bit the drive now threads in correctly and straight. I had to sacrifice a cheapo thread file, but saved a couple of hundred dollars on a custom tap. As always, simpler is better. Thanks for the suggestion.