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gearbox issue?

Submitted by martin_main on Sun, 14/05/2017
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Hi, having read Bob Proudmans interesting stuff on laydown gearboxes, it seems I have a 1951 dominator box with std ratios and the GT165 mainshaft. Its in bits at the moment awaiting new bearings.

As i need to use this box in a rigid frame and coupled to a single cylinder OHV engine, would I need to, and is it possible to, simply swap the mainshaft for the shorter GT175 mainshaft, and all be ok?

I assume there could possibly be engine sprocket, to clutch chainwheel alignment probs?

Any help or guidance much appreciated,

thanks, Martin

Submitted by roy_cox on Sun, 14/05/2017

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Hi Martin

If your clutch is correct for the box which I assume by the date came out of a model 7 you should not have any alignment problems. However be aware that there are 3 different engine sprockets, each with different offsets.

Roy

Submitted by martin_main on Mon, 15/05/2017

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Submitted by martin_main on Mon, 15/05/2017

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Hi Roy, thanks for your reply.

dont know where Dominator came from, I was thinking model 7!

I sounds as if I can stop panicking somewhat from what you say, especially re the 3 spkt offsets.

Delving into a Norton is a little new to me, and I have such a mix of parts...

How could I tell if I have a Model 7 clutch? I could post picture/s of parts if it helps.

Martin

Submitted by roy_cox on Mon, 15/05/2017

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Hi Martin

The pre amc clutch has a steel pressur plate.

The clutch back plate was changed with the introduction of the laydown gbox. The new plate was thicker with a bevelled edge.

A picture should clarify

Roy

Submitted by roy_cox on Wed, 17/05/2017

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Hi Martin

Is it possible to see the other side of pic 174440?

From pic 174511 it appears that you may have the clutch for an upright gearbox. The backplate was changed in 1949 with the introduction of the laydown gearbox.

Is your gearbox stamped with a serial number G101 or G102 or GB8 with 4 following numbers?.

Roy

Submitted by martin_main on Thu, 18/05/2017

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Hi Roy,

please find attached pictures - back of clutch, gearbox main casing and intermediate casing numbers

i hope I'm able to use what I've got.

for some reason the site wont let me attach any pictures to this particular message - but I have been able to attach further pictures to the message I sent the first four in.

Thanks, Martin

Submitted by roy_cox on Thu, 18/05/2017

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Hi Martin

The clutch back plate is for the earlier upright box so you may have alignment problems. However if you are using an earlier engine sprocket, which has the teeth on the widest part of the taper i.e. nearest to the crankcases you may get away with it. The important bit is to ensure that the chain does not rub on the chaincase. The gearbox number is for a single downtube frame.

I think this about the most info that I can give you.

Good luck

Roy

 


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