Can a Smiths speedo drive be driven backwards?

Can a Smiths speedo drive be driven backwards ? I need a Smiths speedo drive # BG5331/107 for a 1970 RE Interceptor with a 150mph speedo and a MK11 Norton one might work but it would be spinning backwards when the RE is rolling forwards .

I would say no.
Dave

The speedo obviously won't work with the cable rotation reversed, and although it's possible to reverse the direction of the output spindle by swapping over the threaded spigot and 'bullet' end cap, I think a 1970 Interceptor MPH speedo might require 2:1 drive ratio if it is a '1600' (cable turns per mile instead of '1000') unit, in which case a Commando (1.25:1 or 15/12) drive gearbox wouldn't be suitable, not even the 850 Mk3 type, which has reversed drive (as it's on the left/drive side on a Mk3) so it's something that should be checked first.

I think it can, but the direction of the output and so the cable will be the opposite of what it was eg clockwise will become anti clockwise.

L.A.B. said:

The speedo obviously won't work with the cable rotation reversed, and although it's possible to reverse the direction of the output spindle by swapping over the threaded spigot and 'bullet' end cap, I think a 1970 Interceptor MPH speedo might require 2:1 drive ratio if it is a '1600' (cable turns per mile instead of '1000') unit, in which case a Commando (1.25:1 or 15/12) drive gearbox wouldn't be suitable, not even the 850 Mk3 type, which has reversed drive (as it's on the left/drive side on a Mk3) so it's something that should be checked first.

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This ^ +1

I swapped my stock wheels for cast aluminum wheels and had to fashion a way to drive my speedometer from the left side, so I swapped the cap and drive end of the right side drive speedo gearbox to make it into a left side drive gear box. The advantage was that I didn't have to buy any new parts, but I did spend a lot of time machining down the hub face to make room for the gearbox inside the fork leg without misaligning the centering of the front wheel. I also had to make a custom flange for the hub to spin the gearbox drive ring, and shorten the existing rear wheel drive cable which looks simple, but wasn't...

A lot of research went into my modification because of the different ratios of smiths speedometers. I thought about adapting a veglia that was already a left hand drive too, but ended trying to modify the drive I had because it was the cheapest route...


here's the thread link below. You can just skip to the 2nd page and see the result.

alternative-right-rear-speedo-drive-t25106-15.html

L.A.B. said:

The speedo obviously won't work with the cable rotation reversed, and although it's possible to reverse the direction of the output spindle by swapping over the threaded spigot and 'bullet' end cap, I think a 1970 Interceptor MPH speedo might require 2:1 drive ratio if it is a '1600' (cable turns per mile instead of '1000') unit, in which case a Commando (1.25:1 or 15/12) drive gearbox wouldn't be suitable, not even the 850 Mk3 type, which has reversed drive (as it's on the left/drive side on a Mk3) so it's something that should be checked first.

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The cable will be spinning backwards if I use the MK111 drive so that's out , the drive spins the cable the wrong way compared to what I need. So what I need is a drive unit that has a 1.25 to 1 ratio, and if turning the rear wheel forward the drive output will be turning the cable clockwise . So if I take a non MK111 drive apart and swap its ends around will it work? The drive on the RE faces "up" and back not "down" and forward like on the non MK111 Norton

It appears the PO of the RE did just that ( the one that was on the bike was damaged and was incorrect however it will be the only one that will work as the correct one is very hard to find, BG 5331/107 ), so all I have to do is find a non MK111 drive and take it apart and swap the ends. Notice in the photo the drive is coming out the other end compared to a normal one on a Norton.
http://www.ebay.com/itm/Smith-Speedo-Ge ... Ei&vxp=mtr

I swapped the worm and blank off end around , however the drive does not reverse. I went through about 6 drives I have which I thought were all for pre 75 Nortons and found one that spins the cable in a different direction from the rest. They all have the same serial number :shock: , BG5330/171 , I am confused again. Unfortunately the drive that spins correctly is damaged, the hub is gone and I do not know if I can fix it.

jimbo said:

the drive spins the cable the wrong way compared to what I need. So what I need is a drive unit that has a 1.25 to 1 ratio, and if turning the rear wheel forward the drive output will be turning the cable clockwise . So if I take a non MK111 drive apart and swap its ends around will it work?

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I think I see the problem.

The original question was: "Can a Smiths speedo drive be driven backwards ?".

However, as your photo shows, the BG5330/171 drive gearbox is on the (normal) right hand/timing side with the output end reversed so the drive gearbox isn't being "driven backwards".
Changing the output end will reverse the cable rotation unless the gearbox is also moved to the opposite side of the wheel.

heres how the gearbox is supposed to turn the cable , note the orientation of the input and output

IF you don't change the speedometer gearbox to the other side of the motorcycle, the ring gear spin direction inside the gearbox does NOT change,... BUT by changing the direction which the cable exits the gearbox, the CABLE'S SPIN DIRECTION is changed.... So you can take a primary (left) side speedo gearbox, swap the "ends" and use it on the timing (right) side... The Gearbox ring gear on the timing side will spin the opposite direction as it did on the primary side, but by reversing the direction that the cable exits the drive unit, the cable will spin in the correct direction for the gauge to work properly.

Which means you can make a left side speedo drive into a right side speedo drive (or visa versa)... Because the ring gear inside the speedo gearbox and pinion teeth are symetrical so they will mesh correctly regardless of their spin direction. (at least it has worked for me so far)

My biggest issue with switching sides was manufacturing a "spur" of some type to attach to a wheel hub that was not designed to drive a speedo gearbox, which would contact and spin the ring gear when the wheel turned.

I hope I've helped.. I think I may be misundertanding the problem... I'll reread and revise if it suddenly hits me...

thanks ,but its the orientation that's the deal breaker, I think. When moving forward the wheel rotates as any other bike does looking at the right side it will rotate clockwise. The drive output looking at the end of the drive unit will spin counterclockwise as shown in the above photo. Heres a shot of the speedo drive on the bike.

Is it possible to take a regular timing side drive unit and rotate it CCW 90 degrees with the cable fitting facing upward? It would be opposite of what your picture shows but a least it would work.

jimbo said:

When moving forward the wheel rotates as any other bike does looking at the right side it will rotate clockwise.

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Yes.

jimbo said:

The drive output looking at the end of the drive unit will spin counterclockwise as shown in the above photo.

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Yes.

jimbo said:

heres how the gearbox is supposed to turn the cable , note the orientation of the input and output

Click to expand...

Yes, but the output spindle still turns in the same direction as before when fitted the opposite way around, but, as the output is being taken from the opposite end, it reverses output rotation if the input rotation remains unchanged, so in order to get it to work the output has to be from the other end.

jimbo said:

thanks ,but its the orientation that's the deal breaker, I think. When moving forward the wheel rotates as any other bike does looking at the right side it will rotate clockwise. The drive output looking at the end of the drive unit will spin counterclockwise as shown in the above photo. Heres a shot of the speedo drive on the bike.

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yeah, the only way to keep the proper orientation on the bike is to get the proper gearbox. Even if you could open up the gearbox and flip the ring gear upside down, it doesn't change the cable's spin direction. The gears on the ring and pinion have to be cut in the mirror opposite way to do that...


As we have said before, you can get the cable to spin in the right direction, but that's with the gearbox in front of the axle pointing upward, not in the stock position behind the axle

o0norton0o said:

jimbo said:

thanks ,but its the orientation that's the deal breaker, I think. When moving forward the wheel rotates as any other bike does looking at the right side it will rotate clockwise. The drive output looking at the end of the drive unit will spin counterclockwise as shown in the above photo. Heres a shot of the speedo drive on the bike.

Click to expand...

yeah, the only way to keep the proper orientation on the bike is to get the proper gearbox. Even if you could open up the gearbox and flip the ring gear upside down, it doesn't change the cable's spin direction. The gears on the ring and pinion have to be cut in the mirror opposite way to do that...
Yep that's what I was starting to think.


As we have said before, you can get the cable to spin in the right direction, but that's with the gearbox in front of the axle pointing upward, not in the stock position behind the axle
Yep that's what I was starting to think.

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However I cant find one .The one that was on the bike does work , has the correct rotation and ratio but its all bent up, curiously it has the same number as one for a Commando, BG5330/171 but somehow it has been modified. Did someone replace the internals( gears that were cut opposite) from the correct gearbox in the Commando case? I do not want to take it apart to find out because I might have to try to use it and I don't want to ruin it. The proper gearbox number would be BG 5331/107

Just because it reads 5330/171 on the back side, does not mean it's a stock item. The plate with those numbers and ratio imprinted is easily removed by prying it outward carefully. Underneath is a thick felt seal and a flat ring, often stuck together with old grease. Somebody cd have replaced just that plate with the numbers on it.

I disassembled a drive that was damaged to find out some things about them. After I drilled out the 4 steel rivets(?) the bushing dropped out.I pushed the center out by supporting the backside driving out the seal carrier and ring gear. However I cracked the body in doing so. How do you remove the ring gear without wrecking the casting?

jimbo said:

After I drilled out the 4 steel rivets(?) the bushing dropped out.I pushed the center out by supporting the backside driving out the seal carrier and ring gear. However I cracked the body in doing so. How do you remove the ring gear without wrecking the casting?

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Once the support ring ("bushing") has been removed, the "seal carrier" can be pried/levered out. The felt seal, large washer and ring gear should then lift out.

So,.. after some long periods of thought (which makes my brain hurt) I've come up with a postulate of sorts...

There are 3 variables:
-which side of the bike the gearbox is mounted on determins the spin direction relative to the gearbox
- which direction on the output shaft is used to exit in the direction of the gauge (being mounted with the output cable above or below the axle)
- which way the gears are cut to spin the cable pinion and cable

Unfortunately, if you chose any 2 variables that automatically dictates the third one in order to get the cable to spin in the proper direction for the gauge to work.

IN the case of chosing the timing side mount with the output cable exiting above the axl, the norton speedo-gearbox gears are cut the wrong way to spin the cable properly for the guage. This means you have to change a different variable to change the spin direction of the output cable OR change the angles to their mirror opposite directions on the drive gears.