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A Comet gearbox ratios and other questions.

kettlrj

Well Known and Active Website User
VOC Member
Are the gear ratios of a prewar A single box the same as a post war box? Are all the gears interchangeable? How many loose rollers are there fitted to the selector shaft? With a full compliment of 3/16" rollers, the selector shaft will not enter the bearing outer bush. Should there be either one or two less than the full amount. Should the rollers be 4.5mm dia. instead of 3/16"?
 

Robert Watson

Well Known and Active Website User
VOC Member
I can answer one of your questions. I believe the gear ratios are the same. I rebuilt my A twin box with late Ariel Sq4 parts. The TTR although having originally come with close ratio dog style gears, came with the same gears as the twin, I did find a set of dog style standard ratio gears (same ratios at the twin and Sq4) from an AJW that are in there now.
I don't recall have any issue with assembly of the selector shaft, but that all happened about 10 years ago!
 

A_HRD

Well Known and Active Website User
VOC Member
I think it's 12 rollers (or in any case the full compliment) and they're definitely 3/16"; not 4.5mm. I've just been and measured the ID of my bush and as best I can tell it's 0.910". Then I measured the OD where the rollers go in the selector-shaft and it's 0.534". Adding the 2 x 3/16 rollers (0.375") to 0.534" = gives 0.909" - same as the bush ID bar 1 thou.

Hold the 12 rollers in place with grease; if one cants over the whole assembly won't go in. My bush has a taper on the inside to assist with easing them in... Best of luck.

Peter B
Bristol, UK
 

A_HRD

Well Known and Active Website User
VOC Member
Just a thought, if you have a slightly mismatched main case and inner cover, you might have alignment problems...??
Peter B
Bristol, UK
 

kettlrj

Well Known and Active Website User
VOC Member
Thanks all,
I took out one roller and everything went together with no problem.
Cheers Richard.
 

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