G: Gearbox (Other - Albion, AMC, Norton etc.) Norton Box: Q- Final Drive Ratio's Comet?

[Jez Nemeth]

Hi folx,

Help/advice -Running 'Standard' AMC/Commando box -Final drive is wrong at present. Having to slip clutch to pull away - feels like pulling away in 2nd or even 3rd, and once underway it's flying -it is 1st though. Bike is intended for road use, not Salt flat records...

Present set up: Front is 18T -rear is 46T off a twin

Standard Comet should be 48T of course

Don't particularly want a game of 'guess the ratio' if I can help it...that's an expensive one player game...
Belt Drive primary and an exact 1.8:1 ratio for a single -as per original spec, Clutch is Norton and smooth as butter.

Advice/experience appreciated, thx in advance jez

 

[Nulli Secundus]

Jez, That gives a 4.6:1 top gear ratio that is actually quite close to the 4.64:1 standard Comet top gear ratio. A 48T rear sprocket would bring you down to 4.8:1. Both those ratios are higher that a DBD34 Gold Star which is 5:1, so you could go lower still I think, if that is what you prefer.

Have you run the bike through all four gears? I just wonder if you have pulled away in second, or third, for it to seem to be such a tall first. Perhaps it is a close ratio box.

Cheers

David

 

[Jez Nemeth]

Thx David -that's really useful info -Been wondering about the box -don't know the history of it unfortunately, but it's certainly been opened a few times before i got to it and replaced seals, bushes, bearings, etc... Something is amiss, selector has been flipped for rear sets so that may have an impact?

New territory for me -ratio's though, and comparison are very helpful.

 

[Nulli Secundus]

For my Rudge race bike I created an Excel file that automatically calculates the primary and final gear ratios for what ever size sprocket that I entered.

The calculation is:-

(clutch Sprocket Teeth/Engine Sprocket Teeth) X (Rear Sprocket Teeth/Gearbox Sprocket Teeth)

 

[Jez Nemeth]

Excellent! I can work with that equation David -just need to make some adjustments for the beltdrive system -but as said, spot on Comet ratio...

 

[Jez Nemeth]

You know -daft as it seems, I haven't tried to pull away in 3rd or 4th...which is possibly one of the first things to have tried...easily remedied...

 

[Comet Rider]

Jez,
At some point it would be helpful to look inside your AMC box, as from memory there are at least 6 different 1st gear ratios you can have.
If I can find it I will see if I still have my little black book of Norton gears and their part numbers.

Neil

 

[Jez Nemeth]

Yes...Think you're unfortunately very right Neil.

If I'm going to get this pinned and be able to get a handle on this, it will need to be opened up.

 

[Nulli Secundus]

Thx David -that's really useful info -Been wondering about the box -don't know the history of it unfortunately, but it's certainly been opened a few times before i got to it and replaced seals, bushes, bearings, etc... Something is amiss, selector has been flipped for rear sets so that may have an impact?

New territory for me -ratio's though, and comparison are very helpful.

If you mean the cam plate has been flipped over I do not think that works Jez. You need a proper reverse action camplate from one of the Norton specialists like Andover Norton, Norvil, or RGM. If you study the attached picture it shows a standard cam plate and a reverse action one. You will see a difference in the selector tracks compared with the cam plate outside profile. I looked into all of this when I built by Norvil and wanted a reversed Production Racer lever and keep the standard down for higher ratio shift pattern.

.

 

[Nulli Secundus]

PS Your gears inside the gearbox might be OK though.