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Laydown Gearbox gear replacement

Submitted by Anonymous on Mon, 06/06/2022
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Heavy Twins

What is the difference between Norton gear N8041 and N8041-3 and can they be interchanged? I am assuming that the "-3 degrees" at the end of the gear number is something to do with pressure angle (?) but why on some gears and not others?  Any help woulld be greatly appreciated as I am just about to start the rebuild the box on my '55 Dommie using some replacement gears sourced from all over the world as the case hardening on some of the original gears had worn through.

Submitted by david_cooper on Tue, 07/06/2022

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Apparently, pressure angle is usually 14.5 or 20 degrees. In any case, not 3 degrees.  Unless you are putting this in a racing Commando, it's not likely to matter (in my opinion...others may of course vary).  I wonder if a book about the Norton gearbox from 1930 to 1975 would become a best seller?

There are a few articles in the Roadholder archive. It could be an interesting challenge to put one together.

Submitted by paul_standeven on Tue, 07/06/2022

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Is 8041 the second gear layshaft pinion?  As far as I know, this pinion stayed the same until part way through Commando production when the ratio was raised to edge past noise regulations. If 8041/3 is the larger closer Commando pinion, then do not interchange with earlier stuff

Paul

Submitted by david_cooper on Tue, 07/06/2022

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The AMC box has three dogs. The laydown ( and dolls head) has four.  (Both have four facing the first gear). So if it's Commando it will fit inside the box but won't engage with number 3!

Submitted by Anonymous on Wed, 08/06/2022

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Thanks Guys for the comments so far.  The N8041-3 is a layshaft 2nd gear with 24 teeth with 4 dogs offside and 3 dogs nearside to mate with N8045 (kickstart ratchet 1st gear) and N8037 3rd latshaft gears respectively. As far as I am aware the N before the gear number denotes a Norton Laydown part so definately not Commando.  The puzzle is that I have some gears marked with a "-3" at the end of the number and others which do not have the "-3".  I cannot see any difference in tooth form and was just curious which too use on the rebuild which is now delayed as I have managed to crack the casing trying to get in a very tight mainshaft bearing (and yes I did heat the casing but obviously not enough - Mick Hemmings video (bless him) makes it look easy - us mortal just have to struggle)!!!!! Now looking for another GB8 casing - it would have been cheaper to upgrade to an AMC box in the first place!!

Submitted by jonathan_newton on Wed, 08/06/2022

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Trust you are in the UK.  If so contact me via email and I will arrange shipment.

 

Cheers

Jon

Submitted by richard_cornish on Wed, 08/06/2022

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Hi Gavin,

  I'm not 100% on this, but I believe this number relates to the gear teeth thickness being reduced to provide the correct back-lash so the new gears would not whine when in use. This method was also used on the single cylinder engine timing gears. The issue here was to address any machining  inaccuracies with the aluminium castings and using old machine tools. Having said that, after 50+ years you will probably have too much back-lash now !

Submitted by Anonymous on Thu, 09/06/2022

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Thanks Richard,

I have done a bit of background reading on pressure angle and measured (as best I can) both the N8041 and N8041-3 gears and both appear to have a pressure angle of approx 20 degrees so the "-3" after the number is nothing to do with pressure angle as far as I can see.  Richard may be right that is something to do with back-lash.  Either way I am now happy I can use either gear in the rebuild as they should mesh OK.

As a "Newby" can I just say what an excellent forum this is and thanks for all your help!

Cheers

Gavin

 


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