Second gear ratio

Just took gearbox apart to replace bearings and bushings and found a broken off tooth on second gear and other wear. I have looked on forum for info on changing second gear ratio to mk3 spec. Lots of info but not much from people who have actually done it from a comparison perspective. I have a 750 combat and most of my riding will be below 70 mph and 5000 rpm. I would appreciate any thoughts since I have to purchase a new gear set anyway.

Haven't done a back to back but it was originally done to meet noise regs, it dropped the revs at the required test speed in second so the noise test was achieved.

I think that was publicised to say that it overcome the noise, but me thinks the OP has answered his own question - and yes, I read the service releases. Remember, the black caps, balanced pipes and the plastic airbox had already been in existence. Had any noise legislation come into force for that period where the MK3 would be sold- maybe someone will know.

As for fitting the MK2 pair, it will not really make a difference to you if you are mostly sat at 70, just a small difference in how you get there which I doubt if you would notice. If it makes the gearbox have an easier life, then the change makes sense.

Madnorton said:

I think that was publicised to say that it overcome the noise, but me thinks the OP has answered his own question - and yes, I read the service releases. Remember, the black caps, balanced pipes and the plastic airbox had already been in existence. Had any noise legislation come into force for that period where the MK3 would be sold- maybe someone will know.

Click to expand...

The high-ratio 2nd gear was introduced on the 850 Mk1A in late 1973 at the same time as the black plastic airbox and black cap silencers, the high ratio 2nd gear set was subsequently fitted to Mk2A and Mk2 (the standard ratio gears are not listed in the 2/2A supplement) as well as the Mk3.


https://andover-norton.co.uk/en/shop-dr ... ansmission

12
MAINSHAFT 2ND GEAR 18T "AHB" '74 On
part-no: 06.4640
13
LAYSHAFT 2ND. GEAR 23T "AHB" '74 On
part-no: 06.4639

Click to expand...

(The gears are marked incorrectly on the AN drawing. The gear to the left is the 18T MAINshaft gear and on the right is the 23T LAYshaft gear, however, the list views show the correct parts.)

Thanks for the info. I think I will retain the stock gearing because I am going from a 19 to 20 tooth countershaft sprocket so I will already be loosing some mechanical advantage. In the 70,s all the 750,s in Canada had 19 tooth sprockets and changing up to even a 20 just seemed to kill the tourque characteristics of the bikes. Almost everyone in my area switched back to 19 at the first opportunity.