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#563592 09/16/14 8:38 pm
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Hi,

The speedo drive gear (6T) on the end of my [email protected] layshaft seems to be a bit bigger that those found on STD layshafts? The outer case of the RRT2 has a standard size receiving gear as found on the STD box.

I am not being familiar with RRT2, but wanted check any implications here as i need to put a drive gear on to my mates new Nova layshaft.

Any advice appreciated.

Thanks.

mike.


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Someone here will surely have the specifics, but you are right to be concerned - yes the RRT/2 speedo drive gears are different - the simple test is to have the layshaft and driven gear (out of the cover) on the bench and lay the driven gear on the layshaft, as it would be when running. The ere should be 90 degrees between the layshaft and driven gear centrelines...if the gears are not a match it will be obvious that, when engaged, they don't beet at 90 degrees.


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Oliver Wendell Holmes
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The RRT & RRT2 boxes have a 6 tooth gear in the layshaft definitely, got the picture on my phone when I fitted mine.
Sorry cannot find the photo of the outer gearbox cover drive..

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From very distant memory, the outer cover driven speedo gear is 10 teeth, rather than 11 of the others..


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Oliver Wendell Holmes
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Speedometer Gear Dimensions

RRT2 LAYSHAFT 6T 0.550 O/D
RRT2 DRIVEN GEAR (COVER) 10T 0.500 O/D

STD LAYSHAFT GEAR 6T 0.470 O/D
STD DRIVEN GEAR (COVER) 11T 0.600 O/D

The gear sets are not interchangeable
HTH
Brian





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Brian's right the RRT/RRT2 HAVE the same number of teeth as a standard but is larger diameter

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Thanks guys for the replies.

I was hoping to put a STD layshaft 6t gear on the Nova layshaft so i could leave the existing layshaft in intact and use a an outer cover from STD box.

I will need to select the gear set which ever ever gives me the most accurate speedo reading, so i guess i need to ask Nova how their layshaft and ratios may affect my speedo reading.

Mike.


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It's interesting you gents are discussing speedo drives as I too have a new Nova gearset I will need to fit with the proper speedo drive gears. Details, details aargh. Any info on a good source would be much appreciated.


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If Nova's top gear ratio is 1:1 (which it is, according to their website, for both close 5 speed and road 5 speed internals), you'll need to use whichever set suits the speedo head you are using. (assuming you change nothing in the final drive gearing).

If you were previously running the bike with a certain setup and it was adequately accurate, use the same if you can.


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uuh Kerry ... The speedo drive gear ratio is dependent on the fixed ratio of the mainshaft/layshaft reduction ratio. Bear in mind the fixed 'B' gear layshaft rpm is a constant being tied to the 'A' output sleeve gear and the layshaft drives the speedo. Only the tranny/rear wheel sprocket ratios changes will cause any indicated error. Don't all Goldies use the same speedo head? I believe so.


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I got mine from Chris at autocycle, the only difference I could see from the BSA originals was that the gearbox box case drive gear did not have a reverse scroll ground on the shaft to pull back the oil..

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I thoughts that what I said, in a roundabout way -I should have read it before pressing go! Basically, yes. I guess the difference with the RRT/2 box speedo drive gears is due to the different internals, with wheel diameter/tyre choice and final drive sprocket choice being the only variables likely to upset the cart.

Never checked, but I suppose they all did use the same speedo head.


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Oliver Wendell Holmes
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Hi Guys,

The instructions for the Nova 5 speed road box mentions to fit the existing RRT2 layshaft gear drive onto the new layshaft. I think there maybe a a presumption that the shell and existing parts will always be RRT2.

Nova are coming back to me on this soon.

Mike.


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The Nova C/R cluster has the same sleeve gear to layshaft ratio as the RRT/RRT2, and require the RR type speedometer gears 6-10

Sleeve gear A 25T
Layshaft gear B 18T

I think the Nova road cluster has 25-17
and the BSA STD cluster has 26-17
So it will be interesting to hear what speedo gears Nova specify

I have found the Nova layshaft has an oversize bore where the 6t speedo gear fits into the shaft,and is far too slack to be satisfactory. I machined the speedo gear shaft smaller, pressed on a sleeve, then machined it to fit the Nova shaft.
This problem may now have been addressed by Nova, as this was a couple of years ago.
Brian




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HI Brian,

The Nova layshaft bore in question is still oversize! I expect the error is in the drawing, not in the machining as they do some very high quality gearboxes and engineering.

They are very receptive to constructive comments and helpful, that is the kind of company i like.

mike.


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My friend got this back from Nova today, we supplied them this information (Thanks DBD Brian)
Speedometer Gear Dimensions

RRT2 LAYSHAFT 6T 0.550 O/D
RRT2 DRIVEN GEAR (COVER) 10T 0.500 O/D

STD LAYSHAFT GEAR 6T 0.470 O/D
STD DRIVEN GEAR (COVER) 11T 0.600 O/D

REPLY:

"This is something we have been asked about before, and the information you have provided proves what I believe to be the case that the speedo drive when used on the Nova road gearbox is 3.8% out based on the ratio difference. This is such an insignificant difference and within the 10% allowance of road vehicles I believe most people don’t go to the hassle of having a new speedo scale. To do it with the speed gear pair you would need to achieve a ratio of 1.906 opposed to the 1.833 used on the standard or 1.667 used on the RRT2. Though with the complexity of a worm drive and based on the negligible difference between the ratios, (and to be honest based on the centre distance I am not sure such a ratio could even be achieved) the costs would be far in excess of what would be acceptable for such a mod.

I hope this information is of use to you."

SO, from the above i am going to use the speedo parts from a STD box on the Nova road box for best speedometer accuracy, and i do not have to touch the existing RRT2 layshaft or outer cover.

I hope this helps, if it makes sense.

Mike.




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Thanks Mike, all good information, and you now have a resolution to your dilemma. I have also found Nova to be very approachable when I have spoken to them on a couple of occasions, and I think they manufacture a very good product.
I also, built another complete gear box, with a five speed c/r cluster, so I could retain the original RRT2 unit in the event of wanting to re install it. I did have to use the 10T speedo gear from the original box, as I only had a spare 6T RRT gear for the lay shaft.
But I think it will remain on the shelf, as I find the five speed far better especially when two up.

Brian


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