Gearbox Top Bolt Spacer

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thunderbolt

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A quick question after a quick answer please.

I have fitted a rebuilt gearbox to a NEW gearbox cradle for my '74 Roadster. The original spacer that goes on the top gearbox bolt is too narrow and slips straight through the space. I can tighten the top bolt but can see the cradle bowing in as I do it. The original spacer is 1/8" (.125").

The gap with the gearbox positioned mid way along the adjustment slot is .175".

Is it normal for the standard spacer to be too narrow.

Is the best solution to make up a spacer that is a tight fit and bolt it up like that. I imagine the bowing of the cradle plate is not a good idea.

Thanks Don
 
NorComCycles said:
No



No



Is the width of the top bolt boss exactly 0.125 narrower than the lower bolt boss (and engine crankcases at the bolt flanges)?



Does the internal measurement (adjacent the isolastic tunnel) match the lower gearbox bolt boss (as well as the engine crankcases where they fit into the front of the cradle)?
Click to expand...

Thanks for the reply Norm,

I will take measurements tomorrow best as I can.

Thanks Don
 
feather bed gearbox top boss is 3.33"wide approx.
commando top gearbox boss is 3.17-3.18"approx
commando top washer of 1/8" is commonly sold and is wrong/skinny...or left out all together
both final gearbox + washer are the same width as a norton heavy twin engine mounting... not exactly rocket science or calculus math

EDIT: Sorry for repeat: took to long to post...
 
dynodave said:
feather bed gearbox top boss is 3.33"wide approx.
commando top gearbox boss is 3.17-3.18"approx
commando top washer of 1/8" is commonly sold and is wrong/skinny...or left out all together
both final gearbox + washer are the same width as a norton heavy twin engine mounting... not exactly rocket science or calculus math

EDIT: Sorry for repeat: took to long to post...
Click to expand...


Thanks Dave for the measurements. So that means there should be a gap of 0.160" and the washer sold for the top lug on the Commando gearbox is 0.125" which as you say is skinny for use in that area.

If the Commando top washer of 1/8"" is commonly sold and is wrong - can you tell me what is the "right" washer to purchase?

Thanks Don
 
thunderbolt said:
Thanks Dave for the measurements. So that means there should be a gap of 0.160" and the washer sold for the top lug on the Commando gearbox is 0.125" which as you say is skinny for use in that area.

If the Commando top washer of 1/8"" is commonly sold and is wrong - can you tell me what is the "right" washer to purchase?

Thanks Don
Click to expand...
Yes Don this is the eternal challenge...finding the right parts, well made and correct. I get along great with one of my supplier who is NOT a norton expert and expects a lesson each time I get a wrong part from him. Not only was mine 1/8 thick but 5/8 hole. Just ask your parts guy for 9/16 hole and that the thickness measures "X" (160-180?). What ever makes the gearbox the same as the engine width.
Instead of a washer, some times a custom long shim can be turned into a fixed but 2 position LH gearbox adjuster for a belt drive. Simple and a lot less expensive than those adjustable dual gearbox kits. have 2 plates made and you can have 4 gearbox positions.
 
thunderbolt said:
A quick question after a quick answer please.

I have fitted a rebuilt gearbox to a NEW gearbox cradle for my '74 Roadster. The original spacer that goes on the top gearbox bolt is too narrow and slips straight through the space. I can tighten the top bolt but can see the cradle bowing in as I do it. The original spacer is 1/8" (.125").

The gap with the gearbox positioned mid way along the adjustment slot is .175".

Is it normal for the standard spacer to be too narrow.

Is the best solution to make up a spacer that is a tight fit and bolt it up like that. I imagine the bowing of the cradle plate is not a good idea.

Thanks Don
Click to expand...

I just measured one that is all original as far as I know. The gap is .130" and the washer is .126" both measured accurately. I checked two others and the washer is close to .125" on both but I didn't unbolt them so I could check the gap or accurately measure the washer. There is no noticeable bowing, but obviously there is .004" since that's the difference.
 
I use a rear wheel axle washer (pre Mk3) it fits between the g/b and cradle "just-so". Never had an issue. The fit is "tight" enough so that the cradle hasn't failed to give back that minimal clearance when the upper bolt is slacked off to adjust the primary chain/belt tension or remove the g/b.

Kinda akin to the old phrase, "If the shoe fits". I sure hope I'm not steering anyone wrong. I am sure that my practice will be labored if not "correct".
 
NorComCycles said:
No

Is the width of the top bolt boss exactly 0.125 narrower than the lower bolt boss (and engine crankcases at the bolt flanges)?



Does the internal measurement (adjacent the isolastic tunnel) match the lower gearbox bolt boss (as well as the engine crankcases where they fit into the front of the cradle)?
Click to expand...

To answer your questions in order.

1. The top bolt boss is exactly 0.140" less than the bottom boss.

2. The internal measurements are as follows: Adjacent to the isolastic tunnel is 3.35"; Lower gearbox bolt area is 3.32".

As a matter of interest the rear axle is NOT 17mm. It is 9/16" (mine measured .556") which is a tad over 14.25mm. I measured two rear axles, my old one and the new stainless one I bought to replace it.
 
dynodave said:
feather bed gearbox top boss is 3.33"wide approx.
commando top gearbox boss is 3.17-3.18"approx
commando top washer of 1/8" is commonly sold and is wrong/skinny...or left out all together
both final gearbox + washer are the same width as a norton heavy twin engine mounting... not exactly rocket science or calculus math

EDIT: Sorry for repeat: took to long to post...
Click to expand...


Dave my measurements to compare with the ones you stated are:

Top boss width = 3.18"
Bottom boss width = 3.32"

This leaves the resulting gap at 0.140"

The gap on my setup with the gearbox installed on the bench is 0.165" and I have found that the old rear axle spacer is 0.162" and fits the space perfectly and even has the correct centre hole (9/16"). Opinion on using this as a spacer.

Thanks Don
 
NorComCycles said:
Here is something to think about. See what conclusion can be drawn from this......

The gearbox top bolt is 9/16 (approx 14 mm). The rear axle is 17 mm.
Click to expand...

The 850 Mk3 rear axle (spindle) is 17mm.
The pre-Mk3 axle is 9/16.
The 850 Mk3 dummy axle external thread is also 9/16.
 
As mine is a '74 (as mentioned in the 1st Post) the top gearbox bolt and rear axle spindle are both 9/16". So the old rear axle spacer (0.162") will work fine.

Thanks for all the input.

Don't hesitate to post though if anyone has any further thoughts.

Thanks Don
 
Put a straightedge along the cradle side to see if flat once you tighten the nut.
 
Recently had my 73 750 gearbox out. Bottom boss 3.300", top3.180", so .120" spacer. Just checked the engine boss most accessible, looks like 3.308".
When I got this beast the upper gearbox bolt was tightened in with no spacer. Both motor mounts were bent in,(left side about .125", right side .0625"), and out of square with the isolastic tube. Don't ask me how this could happen, I'm only reporting what I found. I was able to get things back in a reasonable state, square and straight, things loosely bolted up with no obvious misalignment.
 
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