1963 650SS gearbox sprocket

Hiyah Andy, All sounds good to me. 19 teeth is fairly standard for 650SS and Atlas. I've never run one with 16T - are you sure that's not for sidecar use ? Though it's probably small for that as well. You don't mention chain size or guage.. Standard for that period would be 5/8 X 1/4 inch but it stretched very quickly so they introduced 5/8 X 3/8 inch in 1964. Obviously if your gearbox sprocket is hooked you'll need to look carefully at the brake-drum sprocket. New chain and both sprockets can be expensive but if yours are the narrow ones it may pay you to convert now. Good luck and regards, Howard

hello again Andy - Just checked my 1966 to 1968 Master Parts List for all the big twins from AMC and Part Number 040480 is listed as 19T 5/8 X 3/8 in for 650SS, Atlas, G15CSR, P11 and P11A. All the other big twins used P/N 040451 which was 17T. Perhaps 16T was used on the smaller twins ? Mystery ?? Cheers, Howard

Please check attachment. It is from a Bacon Book but generally the data is correct for the bike years mentioned.

All of the big Dommie twins had a rear sprocket of 43 teeth. This is was the same for the whole range of 650 bikes from Manxman to Mercury.

The rear sprocket went down to 42 teeth when the Commando arrived on the scene in 1969 but did not change for the Mercury bikes despite the engine and gearbox being essentially Commando items. If your present rear drum/sprocket does have 42 teeth then the extended sleeve nuts holding it to the hub will probably have a UNF thread.

The narrower rear chain was used on both early 650 and Atlas bikes. It wasn't chain stretch that was the problem.......rather the narrow sprocket teeth could not handle the power they were asked to transfer to the road. Note that the primary chain remained the same for 30 years, despite the engine power doubling.

Possibly of interest.....the current 961 range of road bikes all use a 525 size rear chain.

Puzzling about the 16T gearbox sprocket. First time I have heard of one in 46 years of Dominator ownership. Could it be it was listed as an option for hauling sidecars? Or even be a misprint?To the best of my knowledge, all 88/99/650/Atlas machines were supplied with a 19T gearbox sprocket 040010. The engine sprockets were 19T 88, 20T 99, 21T 650/Atlas. Engine sprockets were smaller for sidecar use (17/18/19 respectively). The only mention of a smaller gearbox sprocket is 17T for a model 50 and sidecar (something to contemplate!).

All of my 650 spare parts books, up to the change of chain size, show the rear drum/sprocket as p/n 50245 with 43 teeth. Post 1963 it becomes p/n 030052.

They also all show the gearbox sprocket as a generic item with p/n 040010 but no mention of number of teeth or size. Post 1963 the p/n becomes 040480, 19 teeth, 5/8 x 3/8".

The rear chain stays at 97 links in all books for the 650.

The likes of Norvil, list p/n 040010 as a 5/8 x 1/4" gearbox sprocket with 16 teeth. With 19 teeth alternatives...... p/n 012368 5/8 x 1/4" and p/n 040480 5/8 x 3/8".

Finally....... back in the late 60s & early 70s changing the rear sprocket to 42 teeth was an easy way to get 120 mph out of a 650 or Atlas without having to rev the nuts out of the engine. Of course, it only worked if the engine was in perfect condition.

There was a problem with doing this in that the minus 1 tooth left too much play in the rear chain. If you took out a link, the rear wheel then ended up against the swinging arm stops. This then left the choice of inserting a half link or using a worn chain, minus 1 link to get the correct adjustment.

I have referred to this thread, as I have been thinking that my 650SS-engined Wideline is feeling rather busy on A roads, and could possibly benefit from taller gearing. I don't recall reading anything about this in the past, so your thoughts would be welcome. At present it is set up as follows, i.e. bog standard:-

Engine sprocket 21T

Clutch sprocket 42T

Gearbox sprocket 19T

Rear wheel sprocket 42T

5/8" x 3/8" chain.

Many thanks

Ian

When they were designed in the 50's and 60's, there were no motorways so private cars and bikes were designed to rev out at maximum power at maximum speed in top gear.  Low gearing meant winning the traffic light sprint, and journalists (who live in a world of their own) would complain if a vehicle was over-geared (and run faster in 3rd than 4th).

What would worry me about raising the gearing (I only have a 500) would be meeting short steep hills and, especially, re-starting on a steep hill.

Someone out there must have done it and can report back.  Preferably not from Lincolnshire!

But do you have a rev counter?  If not, you might fit one and perhaps be slightly surprised (I was) by how seldom the revs go anywhere near the upper limits.  Ear plugs are, of course vital.  They make my bike go a good 10 mph faster.

Dave. I am not looking to over-gear it, but just to relax it a little. Faster in 3rd than top? Not much point in that! I was thinking of just one additional tooth on either the engine or gearbox sprocket. If the extra tooth on the engine sprocket would assist starting, so well and good. Whilst it may ease the kick-start effort, I think it may lower the engine cranking speed correspondingly, which would be of no benefit.

The SS has a lot more power than the 500, but hills could be an issue, particularly because of the large gap between 3rd & top gear. A re-jigging of the gear ratios to move 3rd closer to top would be advantageous. I am not concerned about hill starts; it will cope. Try them on a RRT2-equipped Gold Star!

It is fitted with a rev-counter. I prefer to ride using the engine torque rather than high revs.

Cheers

Ian

These bikes could really use a 5 speed box with an overdrive 5th gear.  We have fitted the Atlas with the biggest engine sprocket that will fit in the alternator housing and it also has the Commando 42 rear sprocket. It pulls them fine , 

Robert. What size is the engine sprocket? RGM list them up to 25T! Did you need a longer than the standard 76 link primary chain? 

I do agree about the 5 speed 'box, but then, who did equip their machines thus in the late '50's & early '60's? We can now, but at eye-watering prices!

All the 5 and 6 speed boxes whose ratios I have looked at were close ratio sets for racing or fast road use.  Direct top and first gear around 2:1 or perhaps 2.4:1.  No point buying them if you want a usable first gear and a high cruising top gear

Paul

I wonder if it is possible to find a 3rd gear set which makes the ratios more evenly spaced, reducing the big jump from 3rd to top? 

Hi Ian,  Can't remember!, but I to file out the Alt housing and juggle around to get the chain in there.

Hi Robert. I have the primary side stripped out, apart from the rotor & stator, so thought it a good time to maybe change the engine sprocket. I will ponder longer, and leave it for now. Maybe use better ear plugs to drown out the sound of the old push-rodder thrashing away!

Main reason why to fit 5 or 6 speed gearbox on the Manxes was that fitting fairings increased top speed about 10 MPH. When geared for that at the fastest part of the track, first became so high that you have to use the clutch to keep engine on pipe in the hairpins. So an extra first was needed. With the narrow powerband of a race engine, you need close ratios. When I designed 5-speeders for BMW outfits, a 700rpm drop was requested when going from 4th to 5th, due to the wind drag on an outfit. On a road bike where you have a larger usable powerband, wide ratio gearing is better, because you get an usable first for congested traffic and a marked rev drop and subsequently lower fuel consumption when going to top gear. Of course I assume you keep modern speed limits.

I thought they made that change (raising #3) at roughly the date of your bike - or (presumably) just after.  And it is only one gear wheel that needs changing.  By changing one and leaving the other, both the pitch circles change a bit.  So you should only need to change one gear wheel of the pair.

I can't find the info on this site, but it's in the usual books.  I'll look when I get home.

I know they did raise the 3rd gear a little at some point. However, as mine is all Norton, but spanning about 15 years, I am not sure the age of the gearbox. The number is 1294## N, which, if they used the same sequence as the frames and engines, makes it a 1968. Not sure if they did though. I am assuming the N is for Norton, as opposed to AMC. Hopefully not a year code! Anyway, things inside it may have changed. I did rebuild it a few years back, and have a vague feeling I made a note of all the gears; deep digging required for that! Interesting about changing one 3rd gear to raise the ratio. I will investigate.

Cheers

Ian

Ian, your gearbox marked N is an earlier one. My -68 gearbox is marked NA. Main difference I know of is another kick start spring, kickstart shaft and it's bushing in the inner cover. Don't know year of change. I think I've read somewhere that gearbox numbers is a separate series which has nothing to do with engine and frame numbers.

Cheers

Mike

Hello Ian - The gearbox on my 1969 Mercury is 129160 N which is a little earlier than yours so to answer Mikael you can be certain that all the changes that went into the earlier SS and Atlas gearboxes ( that got the prefix NA ) are included in your box.  The Mercury boxes are closely aligned with the Commando box from that period.  The cases are a little different of course and the mainshaft as well, but all the other internals are common.  The change to which you refer with the third gear ratio changing occurred in 1961/2 when the N changed to NA.  This was known as an AMC1 ratio set becoming AMC2.  Good luck, Howard 

On looking in Bacon Norton Twins Restoration, it seems the ratio changes were more complicated. It was 1973 Commando they changed just one gear...and that was main shaft #2.

Third moved close to top in 1960 model year if the book is correct. Main shaft #4 went from 24 to 23 and layshaft #2 from 21 to 20. So in 1960 all the gears moved closer to top, with third making a bit more change than the others.

Thanks Gents. Howard, your 'box is indeed a very close number to mine, at less than 300 apart. It would be fair to assume they came out of the factory with the same spec. in 1969, although mine could be from a Commando at that period of overlap. I am just a little confused by the 'N' & 'NA'. You mentioned that they changed from 'N' to 'NA' in 1961/62. Mikael's is (pre?) 1968 which is still stamped 'NA'. Did they then revert back to 'N' in 1968/69? It would appear to be the case. One wonders what triggered that change, if so?

Interestingly the numbers on our gearboxes are in very similar sequence to the engine/frame numbers at that time. If they were engine/frame numbers, it would indicate late 1968 manufacture.

Meanwhile I am about to see if I can find where I made a note of the gears; if I did?!

Ian

Hello right from  the first Norton 650 built November 7th monday ,  1960  Had fitted as standard gear box sprocket 5/8 x1/4  19 tooth.  Engine sprocket 21 tooth  My Norton 650 manxman  export only built december 1960  has a 22 tooth engine sprocket  to keep the revs down  on long runs  but pulls like a express train LNER  4464 Bittern  now having a good rest in the Hornby factory  Maidstone Kent  and export Norton Manxman's 650 were fitted with Diamond  chains USA  witch you can buy from RGM motors  Diamond chains were one of the best chains you could buy  in them there days    I have  one spare  yours  Anna J  

Anna. Is there sufficient adjustment to allow the use of the standard 76 tooth primary chain with the 22 tooth sprocket?

Ian

Hi Ian and others,

I recently fitted a 22 engine sprocket to my 650 Mercury. I also fitted the later Commando raised second gear set. I can confirm that both mods are well worth doing, hill climbing performance (solo) does not seem to have suffered to any noticeable degree, and is more than adequate for use around the North York moors. I used new standard length primary and rear chains. They were a little tight initially, but a short run loosened things off. Starting is fine, usually first or second kick.

My 1968 gearbox is stamped129178M, no N or NA despite the numbers being close to those mentioned above.

Another Norton (or AMC) quirk?

best regards,

Chas

hello yes but you need a half link fitted in the chain  you can get half links  I have a few  you need to get the gearbox as far forward as you can as well as the rear wheel and once fitted just adjust from there with 3/16ths slack in chain ever run chains to tight and make sure its not knocking on anything 

                             yours   anna j   

That is a nuisance, as I ordered a 22T sprocket from RGM yesterday. I will move the gearbox as far forward as it will go, as you say Anna, and see how it goes.

Do you know the number of teeth in all your gears, Chas? I have found the notes I made on mine when the 'box was last apart. It would be interesting to see where they differ. It is not 2nd gear I feel needs raising, it is 3rd.

Ian

Hello again Ian and Chas,  sorry for the delay in answering but I have been away for a few weeks.  I also owned another Mercury gearbox with the number 129493 N which is even closer to yours.  When Norton Villiers introduced the Mercury model in 1968 they used a similar numbering sequence to Commandos wherein the frame, engine and gearbox numbers all tally.  There is still some confusing element to this numbering system because like Chas one of my other Mercurys had the number 129279 M  and I have seen absolutely no difference between the box with suffix M or N.  I owned the bike with the suffix M before the other box came along so I had assumed that the M signified Mercury but I was never satisfied that that was the case. In recent years I have seen plenty more Mercurys some with suffix M boxes and some with suffix N.  It remains a mystery to me.  Kind regards, Howard   

Ah well, the plot thickens! No worries, it is really out of acedemic interest.

I have installed the 22 tooth engine sprocket, with a new standard length primary chain, which fitted ok with the gearbox pushed forward. It then allowed a little rearward adjustment to get it just so.

On the road it really does make a difference, with a more relaxed feel. Bottom gear is fine, hill starts are fine, and in top gear on winding Cornish roads it will pull up hills comfortably from 50mph in top gear. That is with a single carb.

Pulling in for a pasty, my mate on his very original 1957 99, who had been struggling to keep up, commented that he didn't think it was wise to thrash these old bikes, so it came as a surprise to him when I said I wasn't! With higher gearing than his, higher again with the bigger sprocket, and the considerable extra power of the SS over the 99 made for easy progress by comparison, and I didn't go over 4000rpm.

Well worth doing.

I am riding it to France in a couple of weeks; fingers crossed!

Cheers

Ian

ps just edited a typo; I wrote gearbox sprocket; should be engine sprocket

Down under, here in the great southern land, most Commando and Dommi riders fit a 20 or 21 tooth gearbox sprocket. We often have long distances to travel so the motor feels more comfortable lower down the rev range.

I have a 21 tooth sprocket fitted to my Atlas. Living in the eastern suburbs of Melbourne close to mountains and hills I find staying in 3rd gear in built up areas not a problem as the Atlas pulls easily in top gear in the country side. Sometimes on certain gradients it's a juggle between 3rd and top but you get that with most ratio's [ unless a 19 tooth sprocket is fitted ]

If I was living in the UK and not blasting down motorways I think I would go for a 20 tooth gearbox sprocket. Taller than 21 could strain the transmission!

Hi Ian,

my sprocket sizes are engine 22 teeth, clutch 42 teeth, gearbox 19 teeth, rear sprocket 42 teeth. As stated previously , this combination works really well for me.

My main problem was the large gap between 2nd and 3rd gears, addressed by fitting the later Commando set. If you raised third gear, assuming this is possible, it would exacerbate the problem by making the gap even larger. Also my understanding is that it is technically inadvisable to change one gear of a pair, though this may work out fine in practice.

I fitted the standard length chains front and rear and after a few hundred miles I had to move the gearbox back as the primary chain had become too slack, no half link needed! Half links are not good practice!

Best regards to all,

Chas

Hi Ian,

my sprocket sizes are engine 22 teeth, clutch 42 teeth, gearbox 19 teeth, rear sprocket 42 teeth. As stated previously , this combination works really well for me.

My main problem was the large gap between 2nd and 3rd gears, addressed by fitting the later Commando set. If you raised third gear, assuming this is possible, it would exacerbate the problem by making the gap even larger. Also my understanding is that it is technically inadvisable to change one gear of a pair, though this may work out fine in practice.

I fitted the standard length chains front and rear and after a few hundred miles I had to move the gearbox back as the primary chain had become too slack, no half link needed! Half links are not good practice!

Best regards to all,

Chas