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Why no overdrive 5 speed cluster.?

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It seems to me that a conventional  ratio 4 speed  with a 5th overdrive  would be a good  seller. But as far as I am aware no one makes such a set  for  the AMC box.  This would also enable you to lower the  overall  ratio to give  easy traffic crawling , hill starts  and  more comfy 4th gear town running.

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The problem is that in top gear the gearbox is effectively doing nothing. Top gear just locks the mainshaft (input shaft) to the sleeve gear shaft (output shaft) and all the gears are just spinning around with no load on them. This means introducing an extra gear will always be lower than top gear and just moves the gear ratios closer to each other. 

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There are 5 speed close ratio boxes for racing, so there is enough width.  If the trials first gear sprocket size could fit inside the case, that would allow a larger engine sprocket to increase the top gear direct drive ratio.

I suspect the real issue is commercial, not technical. It's about 30 years too late!

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As there is a selection of gearbox sprockets there is no need for a overdrive 5th, just fit the box and gear it with a larger gearbox sprocket for 4th to be the same overall ratio as in the 4 speed and then 5th will be a higher gear.

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Hi Robert.......The AMC2 gearbox fitted to the Norton Twins, from 1961/62 onwards, was a really good compromise for a 4 speed unit and to some extent did away for the need of a complex and expensive 5 gear set-up. Certainly the torque and power of the 650 and 750 engines gave riders  easy pulling away from a stop or up a gradient. Plus a max speed of over a hundred or  economical 70mph cruising. This box to some extent also suited the smaller twins with their smaller engine sprocket.

The pre-1962 AMC1 box had the huge gap between 3rd and 4th gears, effectively making top an overdrive. It is relatively easy to convert and AMC1 to an almost AMC2 box to narrow the ratios and improve the riding experience. Just change the gearbox 24 tooth output sleeve gear to a 23 tooth version. It should fit straight in with no other changes needed. Though good engineering practise would be to change its partner layshaft gear at the same time but this one keeping its original number of teeth. (usually 18) 

The above conversion raises the 3 lower gears and so narrows the gap between 3rd and 4th.  The potential top speed is unchanged but pulling away from rest a little harder.

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When fairings became common among serious racers, top speed increased some 5 to 10 Mph. That meant that properly geared, you have to slip clutch in the hairpins. So a lower first was needed not to overheat the clutch. Arrgard, Schafleitner and Quaife made them. Maybe some more. Today I think Quaife and TTI are the only suppliers. One of the reasons why they make complete boxes, not clusters to fit an ordinary shell is that some weaknesses in the AMC box can be rectified. For weight concerned riders they also make magnesium shells. The heavy twins has a wider power band so the need for a 5th gear with modern speed limits is not so great. A Manx which has to be kept over 5000 rpm is easier to ride with a 5 speed box. But still difficult to ride at low speed in the pits. Once out on the track, no problem.

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Interesting Phil; Is the AMC 2 normally fitted with a 23 T Sleeve gear? and would it not be wise to  insert its paired (42 count) gear? 

Are the AMC 1 and 2 boxes easily identifiable, or do you just count the turns to determine which you have?

 

Thanks

Jon

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With some minor adjustments to the engine plates, I now can remove the gearbox with engine in the frame on the Manx. Only have one strong son and he's only available on some weekends. But most gearbox work can be done without removing it.

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Hi Peter.  Yes thats the way its normally done.      My  leader on the 5 speed box seems to have sparked some interest,    I could just fit a bigger engine and raise the gearing, but  then I would be in the same position as with the Atlas, can't start it ! ,  The 99 could really use a lower first for traffic crawling  (thats not going away anytime soon) , a slightly lower 4th  for   staying  below the 30 limit  without  having to keep dropping in and out of 3rd , and a  5th  for   keeping up with  the motorway traffic at reasonable revs and ecconomy.  Perhaps  a  BSA  or  Triumph box ??.  or is that some sort of  a no no !!.

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The pre AMC boxes (dolls head and I believe lay down) have the same layshaft first gear (with kick-start inside), but the small main shaft first gear does not have the same boss on the outer end.  I imagine a thick hard washer could make up the difference in width?

Good document to have.  I was interested to know if there are visible external difference or markings to identify an AMC 2?

 Thanks

 

Jon

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It would be very unusual in a box with sleeve gear, like all the Brit bikes of the 60's, not to have top gear through the sleeve gear. The general assumption in design is that the top gear runs for longer and with higher throttle settings than the lower gears. As Ian Goodhall states the gearbox losses are minimal in top gear because the gearbox is unloaded and the clutch connected direct to gearbox sprocket. Anyone know of a gearbox design like this where sleeve gear is not top gear?

Overdrive boxes for cars had their own casings, gears and bearings, so did not add to gearbox loads and losses.

Jap bikes introduced us to the indirect gearbox where the clutch is on the main shaft and the gearbox sprocket on the layshaft. In top gear, in fact through every gear, the drive is taken though a gear and pinion with power losses accepted. Less power losses if rolling element bearings used throughout. Concentric gear forms. Good control of gear diameters and backlash. Good lubrication. A few needle rollers. I believe with this approach boxes with more than 10 gears have been produced for racers.

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I intend to carry on riding bikes into my eighties  and am  considering  what I can do  to make my favourite  old  bikes  more suitable ,  till the time when I have to switch to something  new,  I suppose I should consider  an Electra,   but spares  do appear to be an issue.

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... an old copy of classic bike magazine and came across an article about the 50cc Yamaha (I think) racing twin with a 14 speed gearbox! It had a power band between 17,000 and 17,500 rpm according to the article.

My 1952 ES2 with laydown box has a very nice relationship between 3rd and 4th but there is a bit of a gap down to 2nd. I was wondering whether I could fit the 2nd gear pair from an AMC3 box although of course this would then have a huge leap from 1st.

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Hi Ian,

It was a Suzuki 50 twin, not a Yamaha. Stuart Graham won the 1967 World championship on it. Power band was as you say.

By contrast, Honda's 50 twin 4 stroke had to manage with 'only' 12 gears, despite a 22000rpm red line. 

Certainly no overdrive to help Robert!

Regards, George 

In reply to Robert Tuck

I sympathise. I had a new hip a few years back (at 54) and after a suitable recovery period I went to look at  Bonneville 750 (pre electric foot..) and  I could not start  the damned thing - maybe the Norton gods were warning me ;-)

So, I got a Norton Model 50 which is lovely, unless you want to travel a bit further way as it's not very keen on 50-55mph+ for longer periods.. But at least I can start it ;-)

The big down side is that it's the worst bike I have ever owned by the longest way for getting on the main stand.. If I can't address this then I have to find something more user friendly. Next change will be the later roll-on type centre stand when the NOCShop get some in stock, and see if that helps

My local Norton specialist says he can put a side stand on it that doesn't just rotate around the bottom frame tube and make a mess of it all, but I am a bit sceptical..

 

 

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Ian...the late AMC main shaft second gear has three dogs to engage with third gear. The doll's head has four. I think the lay down is like the doll's head with four; in which case you need to change 3rd and 2nd. Can someone confirm?

There are some notes in one of the archive Roadholders on mixing and matching gears but I haven't seen a definitive description of the possibilities all the way from the first four speed Sturmey Archer all the way to the 850 Commando AMC.

Layshaft 1st (with kickstart) stayed the same for all Norton boxes. Mainshaft 1st (the small one) acquired an end boss for AMC buy is otherwise unchanged, so the boss can be removed on a lathe if you want to use it in an early box.

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I've just had a new (right) hip in September and am fully back to normal although am waiting for better weather before riding the ES2. I have started it though without too much trouble. I previously had the left knee replaced about 10 years ago and it has been no trouble although the bend is slightly less than the original.

In terms of side/prop stands, I posted some time ago about the one I have fittted to my bike using a Kawasaki item and an extra front engiine plate - it works very well. I agree about the centre stand which is a nightmare on my plunger framed bike and sometimes needs my wife's help! I attach a couple of photos of my prop stand.

stand 1

stand 2

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I know the old grey cells aint what they used ta be, but as a bike-mad schoolboy I recollect a TT issue of "The Motor Cycle", would be around 1965 or so. Reported on Mike The Bike's TT tiddler (Honda twin??) with a gazillion gears, and the article showed a photo of the top of his boot with a hole worn through the leather due to constantly changing gear.....

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... the side of his boot worn away on the road surface?

I agree with you Ian, it was taken when Avon brought out their new hysteresis rubber tyres and the put a set on Mikes bike. Then they let him go around one of the race circuits and he could lean over that much further he wore through the sole and side of his boots with his socks showing thro’.

where have all the years gone.

Regards

Dick

 

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