Speedometer Drive Modification (to prevent warping)

I noticed several posts about speedometer drive failures. I have seen numerous pictures of Norton Commandos with the speedometer drives obviously running into the hub cap. I thought I would share the modifications I have done.

First of all I was wondering why my Norton Commando speedometer drive would deform. As a matter of fact mine became so deformed that not only did the speedometer drive housing rub into the hub cap, the gear retainer wore a groove into the wheel bearing retainer. It got so hot due to friction that the zinc casting appeared to be on the verge of melting. I never had this problem with my BSA's.

So I thought I would study to see what the difference was between the two different makes of bikes. Basically what I determined is that Norton uses a smaller diameter of axle and also the spacer between the speedometer drive and the swing arm is rather long in comparison to a BSA unit. While riding the Norton motorcycle there is quite a bit of dynamic load on the spacers that sandwich the speedometer drive. Seeing how the spacer is longer than those used on BSA motorcycles there is more leverage at the speedometer drive. This rocking action on the spacers probably causes the zinc casting to get hammered which eventually deforms the speedometer housing.

I thought why not just get rid of the zinc in the speedometer housing. So I machined a one inch diameter bore in the middle of a good used speedometer drive housing. Then I fabricated a steel double stepped bushing and riveted it to the housing using AN426AD3 rivets. With this design there is absolutely no zinc sandwiched between the spacers. I used this speedometer drive for a couple of hundred miles and it seemed to work just fine. Here are a couple of pictures.

First revision of the speedometer drive modification




Then I got to thinking - why not make a speedometer drive mount that incorporates not only the top hat bushing in the speedometer drive but also the inner spacer (the less spacers the better). I fabricated a spacer out of chrome moly steel that is step bored and has a mounting flange on it that doubles as a gear retainer and also as a mount for a speedometer drive. This one spacer effectively replaces the inner spacer, speedometer drive and the top hat bushing. Then I got a new replacement speedometer drive from Andover Norton and modified it by boring a one inch diameter hole in the middle and then counter sinking the four rivet holes to accept four 4-40 flathead screws. When assembling I used a smear of silicone seal between the speedometer drive and the mounting flange. I did not use any loctite on the screws because I wanted to see whether or not the screws would have a tendency to back out in use. With this speedometer drive mount I could not use the original felt seal that is used for the wheel bearing. I simply replaced the wheel bearing with a sealed type of bearing.

I put 6000 plus miles on this speedometer drive and then I dismantled it. The speedometer drive appears to be in excellent condition. The mounting screws were still tight, the gear teeth just showed polishing but no real wear and the same with the ring gear that rubs against the zinc housing. I feel as though this speedometer drive will last a very long time. The lubricant I used is just a general purpose grease that you can get at any auto parts store.

Here are some pictures of my 2nd revision of speedometer drive mounts.

These two pictures show the speedometer drive mount/spacers.




Here is the speedometer drive mount/spacer mounted on the bike without the speedometer drive itself to give you an idea about how it looks.



Here is an exploded view of the speedometer drive assembly



Here are a couple of pictures of the speedometer drive all assembled




I also modified the outer spacer by shortening it .080 of an inch which makes mounting the wheel a lot easier. Another thing I noticed on my bike is that the brake drum rubbed against the wheel hub. So I ended up machining the brake drum at the place where it rubbed because that may have also caused some of the spacing problems while mounting the wheel.

Here is a picture of where I machined the drum



Overall I am happy with my second speedometer drive modification even though the first revision will probably last a long time as well.

Nice mod. Maybe you should go commercial with it. There are lots of us suffering the "speedo bulge"

Slick

Yeah man PeterJoe that is something we could use that is still steam punk mechanical. Very satisfying to see your will power and thought forms manifest a long time. How steady is the speedo needle?

Now carborize and heat treat the drive gear and the drive will last many years. Jim

Great stuff Peter Joe. Please consider making some of the bushings or hats for sale; we recognize the complications of sourcing drives so you might leave that part, along with boring and drilling and fastening them up to us.

Thanks for the replies and encouragement. I may consider having these spacers made. I am an amateur self taught machinist enthusiast. I have a WWII vintage 9 inch South Bend Lathe with basic tooling. For me to make a bunch of spacers would not be cost effective. However, I do know someone local that has a CNC machine shop and does production work mainly making performance car parts. I will approach him and see what it takes to go into production. As far as modifying the speedometer drive, it's a fairly straight forward job. On my speedometer drive I bored the hole out using a 4-jaw chuck on my lathe which is a time consuming way of boring a hole. I would have to come up with something more efficient. Countersinking the screw holes is pretty quick and easy.

The speedometer drive itself I bought from Andover-Norton however I believe it is manufactured by L.F. Harris in the UK. From what I have read the gears have already been hardened. However, I could be wrong. Documentation is hard to get. Unfortunately this speedometer drive is made a little differently than the original Smiths speedometer drive so that a different spacer would have to be made for the Smiths unit. It doesn't make sense to make several different sized spacers to fit the various brands of speedometer drives. I do not have any information as to the dimensions of the Far East manufactured speedometer drives and would prefer to stick with the ones made in the UK.

Hobot asked if my speedometer needle bounced much. I would say no. It runs pretty steady. The speedometer cable is original to the motorcycle and the speedometer itself is original and made by Veglia in France. The bike has 20,000 miles on it now and the speedometer has never been worked on.

I will keep you posted. Thanks,
Peter Joe

Thank you for doing that Peter. I see we are not too far apart, I'm in Sylmar.

PeterJoe said:

Thanks for the replies and encouragement. I may consider having these spacers made. I am an amateur self taught machinist enthusiast. I have a WWII vintage 9 inch South Bend Lathe with basic tooling. For me to make a bunch of spacers would not be cost effective. However, I do know someone local that has a CNC machine shop and does production work mainly making performance car parts. I will approach him and see what it takes to go into production. As far as modifying the speedometer drive, it's a fairly straight forward job. On my speedometer drive I bored the hole out using a 4-jaw chuck on my lathe which is a time consuming way of boring a hole. I would have to come up with something more efficient. Countersinking the screw holes is pretty quick and easy.

The speedometer drive itself I bought from Andover-Norton however I believe it is manufactured by L.F. Harris in the UK. From what I have read the gears have already been hardened. However, I could be wrong. Documentation is hard to get. Unfortunately this speedometer drive is made a little differently than the original Smiths speedometer drive so that a different spacer would have to be made for the Smiths unit. It doesn't make sense to make several different sized spacers to fit the various brands of speedometer drives. I do not have any information as to the dimensions of the Far East manufactured speedometer drives and would prefer to stick with the ones made in the UK.

Hobot asked if my speedometer needle bounced much. I would say no. It runs pretty steady. The speedometer cable is original to the motorcycle and the speedometer itself is original and made by Veglia in France. The bike has 20,000 miles on it now and the speedometer has never been worked on.

I will keep you posted. Thanks,
Peter Joe

Click to expand...

You may be right in that the new gears are hardened.
After I did a similar mod to my old smiths gearbox it became pretty predictable. No more warping but the drive gear would loose it's teeth after around 20,000 miles.
After hardening the drive gear it lasted a long time.
When I hardened the drive gear it shrunk enough that I had to turn down the hub a few thousandths to get the gear to side over it.

I just made a spacer with a step on it to fit through the drive after the hole was opened up. I then used a cupped spring washer on the outside to hold the body of the drive snug up against the step. I worked well and is a lot simpler than bolting it to a spacer. Jim

What is the latest on speedometer drives?
Any recommendations on who to buy one from or which one is best ?
My last one was junk from day one - some kind of knock off

xbacksideslider said:

What is the latest on speedometer drives?
Any recommendations on who to buy one from or which one is best ?
My last one was junk from day one - some kind of knock off

Click to expand...

Years ago in the Norton News someone had drawings on a brass retainer to take the place of the POS stamped steel one. My tech Digest said it was in NN #91.
I have had 1 done years ago by a machinist at work, love to get another one done.

John in Texas

Can you post drawings for the modification?
John in Texas