Smith Tacho Drive Gearbox Rebuild
- Thread starter AgentX
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Oh, right, I forgot the spade reaches inside the end of the outer housing. Hadn't had my second cup of coffee yet. I'll measure it when the spade adapter's in place. Thanks!
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Luckily for me, mine are all metal, but yeah, I've just been using a heat gun from the outside to get things warm to the touch.
Agent X: I don't know how far in it should be. The tach drive on my G15 is missing parts. I was just going on my experience with speedo problems.
A way to check would be next time the drive is apart, assemble the system without the bottom plate in place. cable to tachometer too so as to eliminate any slack that might be there. See how the gear rides in relation to where the cover plate sits. HTH
A way to check would be next time the drive is apart, assemble the system without the bottom plate in place. cable to tachometer too so as to eliminate any slack that might be there. See how the gear rides in relation to where the cover plate sits. HTH
Agent X: I did some head scratching.
I have a 68 N15 chopper that I bought about thirty years ago.
When trying to fix it up, i found that a repair to the headstock would be suspect, so I just ended up putting parts into boxes.
I went and dug through the boxes to see if the gearbox was there and intact.
I did find it. The threaded portion the cable attaches to was sheared off where the threads would have started, but the sleeve inside of it was still there, much in the same way the one on the 66 G15 was.
The one on the G15 had the bottom plug and driven gear missing.
I also had the tach cable from it and the spade that the cable slides into.
It looks different from the one posted earlier. The flat spade is 17/32" long from the edge of the groove for the snap-ring.
Both plugs were in place and by turning the drives, I could see it was a 1-1 ratio.
The plugs themselves look to be a bit concave and have a witness mark from something like a gasket hole punch in the center of them on he convex side.
This punch looks to have flattened and pushed out the edges of the disk deeper into the groove.
I can't post pictures until my daughter comes to visit again (yes she has tried to teach me before, maybe this time it will stay with me).
I can send pictures from my FLIP Phone to someone if there is interest in this, or I'm 45 minutes southeast of Madison WI, if someone wants to take a look and post pictures.
Frank Coleman
P.S. The snap-ring looks to keep the adapter from pushing down into the gearbox as it rides on top of the sleeve that it fits into.
Similar to the one shown here.
I have a 68 N15 chopper that I bought about thirty years ago.
When trying to fix it up, i found that a repair to the headstock would be suspect, so I just ended up putting parts into boxes.
I went and dug through the boxes to see if the gearbox was there and intact.
I did find it. The threaded portion the cable attaches to was sheared off where the threads would have started, but the sleeve inside of it was still there, much in the same way the one on the 66 G15 was.
The one on the G15 had the bottom plug and driven gear missing.
I also had the tach cable from it and the spade that the cable slides into.
It looks different from the one posted earlier. The flat spade is 17/32" long from the edge of the groove for the snap-ring.
Both plugs were in place and by turning the drives, I could see it was a 1-1 ratio.
The plugs themselves look to be a bit concave and have a witness mark from something like a gasket hole punch in the center of them on he convex side.
This punch looks to have flattened and pushed out the edges of the disk deeper into the groove.
I can't post pictures until my daughter comes to visit again (yes she has tried to teach me before, maybe this time it will stay with me).
I can send pictures from my FLIP Phone to someone if there is interest in this, or I'm 45 minutes southeast of Madison WI, if someone wants to take a look and post pictures.
Frank Coleman
P.S. The snap-ring looks to keep the adapter from pushing down into the gearbox as it rides on top of the sleeve that it fits into.
Similar to the one shown here.
Last edited:
texasSlick
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As I promised above, I would post my evaluation of a newly made tach drive gearbox form Sppedograph Richfield.
I had previously emailed them with the question "Are these NOS Smith's?" I interpreted the answer as, they were made from NOS Smiths parts, supplemented by their own gear making machine shop.
Looking over the newly arrived gearbox, I find:
The housing is cast aluminum, no plastic anywhere to be seen.
No casting marks indicating 'Smith's', 'made in england', or the gearbox type/model number.
It appears that some cast in ID or name was intentionally ground off a boss on the end where the drive gear cap is found on the original Smiths. The newly made has a cast closed end in this location .... no caps to lose at this end. See Fig 1 below
<Fig 1>
The cap at the end opposite the output shaft is retained by a cotter key. See Fig 2 below.
<Fig. 2>
The drive end has a cover plate secured by two slotted screws. I wanted to remove the plate and have a look under, but found the screws to be very tight, so I left it alone. See Fig. 3 below.
< Fig. 3>
There is a ball bearing on the drive end, a nice improvement over original. Let's hope there is a seal in there as well.
Overall, it looks like a well made device and not a cheap knockoff.
Slick
I had previously emailed them with the question "Are these NOS Smith's?" I interpreted the answer as, they were made from NOS Smiths parts, supplemented by their own gear making machine shop.
Looking over the newly arrived gearbox, I find:
The housing is cast aluminum, no plastic anywhere to be seen.
No casting marks indicating 'Smith's', 'made in england', or the gearbox type/model number.
It appears that some cast in ID or name was intentionally ground off a boss on the end where the drive gear cap is found on the original Smiths. The newly made has a cast closed end in this location .... no caps to lose at this end. See Fig 1 below
<Fig 1>
The cap at the end opposite the output shaft is retained by a cotter key. See Fig 2 below.
<Fig. 2>
The drive end has a cover plate secured by two slotted screws. I wanted to remove the plate and have a look under, but found the screws to be very tight, so I left it alone. See Fig. 3 below.
< Fig. 3>
There is a ball bearing on the drive end, a nice improvement over original. Let's hope there is a seal in there as well.
Overall, it looks like a well made device and not a cheap knockoff.
Slick
These are pictures of how I had said it looked like the caps were dish shaped and then flattened/spread out with a hollow punch.
That being said, I think the one shown by Texas Slick would be the better option than dealing with these after they have already come apart.
That being said, I think the one shown by Texas Slick would be the better option than dealing with these after they have already come apart.
Onder
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I am in tacho gearbox land right now, have read through the thread and I wish to know how Slick made out with the new gearbox in service.
Of course my question is does it LEAK? I have a ball bearing type replacement on my Interceptor and it works fine but leaks
badly. Having two identical engines the one with the original bush bearing type leaks very little. Pix shows the new ball bearing type after 20 miles....the leak appears to be out the top where the cable attaches. If you blow on the threaded end and the
gearbox is off the bike you can see it push oil out through the shaft on the cam side.
Of course my question is does it LEAK? I have a ball bearing type replacement on my Interceptor and it works fine but leaks
badly. Having two identical engines the one with the original bush bearing type leaks very little. Pix shows the new ball bearing type after 20 miles....the leak appears to be out the top where the cable attaches. If you blow on the threaded end and the
gearbox is off the bike you can see it push oil out through the shaft on the cam side.
Attachments
texasSlick
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@ Onder
Wow! That is a major leak.
To answer your question, I have put the new gearbox in my spares bin, and am running my original drive. The weep from my original drive appears to be gone. I wrote above (reply #35) what I did to stem the weep.
I would say your leak is due to a failure at the drive end, not at the end caps or output shaft.
I am not familiar with gearbox drives mounted at the timed breather port, but it seems to me your engine is pumping oil directly into the gearbox. Oil has nowhere to go except escape at any available joint.
Slick
Wow! That is a major leak.
To answer your question, I have put the new gearbox in my spares bin, and am running my original drive. The weep from my original drive appears to be gone. I wrote above (reply #35) what I did to stem the weep.
I would say your leak is due to a failure at the drive end, not at the end caps or output shaft.
I am not familiar with gearbox drives mounted at the timed breather port, but it seems to me your engine is pumping oil directly into the gearbox. Oil has nowhere to go except escape at any available joint.
Slick
