Author Topic: 5 speed Gearboxes - B series.  (Read 564 times)

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MGI

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5 speed Gearboxes - B series.
« on: 07 May, 2021, 10:11:06 »
Does anyone manufacture a 5 speed gearbox which can be installed into a B series machine. If so, any idea as to approximate cost & any feedback as to whether, given to torque characteristics of the singles, it is a worthwhile proposal?

Pete C

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Re: 5 speed Gearboxes - B series.
« Reply #1 on: 07 May, 2021, 10:42:00 »
I've never heard of a 5 speed box but I could be (and often am) wrong  ;D

The way we use these bikes now is a bit different to the way they were (ab)used when they were the only form of transport for a family.

Consequently I think they are a bit under geared and I have installed engine sprockets with a couple of extra teeth on both B31 and B33 bikes. It makes quite a difference on how busy the engine feels at that 55-60 mph range. Much cheaper than a set of gearbox internals - check out the 5 speed conversions for Triumphs and think how many beer tokens that represents! :'(

DAVE BRADY

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Re: 5 speed Gearboxes - B series.
« Reply #2 on: 07 May, 2021, 11:21:45 »
Hi,

There are 5 and six speed clusters that fit the A/B gearbox.  I think the 6 speed is aimed at racing Gold Stars and there are options on clusters with 5 speed.
If you google 5 speed gear box for A10 you should find plenty of info.  Nova is one company that springs to mind.

Dave.

MGI

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Re: 5 speed Gearboxes - B series.
« Reply #3 on: 07 May, 2021, 16:18:30 »
Many thanks Dave!

Rog1

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Re: 5 speed Gearboxes - B series.
« Reply #4 on: 09 May, 2021, 10:59:29 »
I've never heard of a 5 speed box but I could be (and often am) wrong  ;D

The way we use these bikes now is a bit different to the way they were (ab)used when they were the only form of transport for a family.

Consequently I think they are a bit under geared and I have installed engine sprockets with a couple of extra teeth on both B31 and B33 bikes. It makes quite a difference on how busy the engine feels at that 55-60 mph range. Much cheaper than a set of gearbox internals - check out the 5 speed conversions for Triumphs and think how many beer tokens that represents! :'(

Just a couple of days before I saw this thread I'd been thinking my M33 could easily pull a higher ratio, but I like the relative simplicity of having just four gears to choose from. I like the idea of just raising the gearing instead, and I'd already thought that the bike would easily pull a 10% higher gear. That's even though the M33 is geared 5% higher already.

Pete, did you tend to cruise at a higher speed and/or find your mpg improved when you raised the gearing?

MGI

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Re: 5 speed Gearboxes - B series.
« Reply #5 on: 09 May, 2021, 12:21:13 »
I had a similar idea, but having spoke to Steve Tomkin who has apparently sold about 200 of these gearboxes (he spoke very highly of them and of Nova who made and still manufacture them) and learned the top gear remains the same at 1:1 somewhat detracts from the original motivation!

DAVE BRADY

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Re: 5 speed Gearboxes - B series.
« Reply #6 on: 09 May, 2021, 13:00:01 »
Hi,

Top gear can only ever be 1:1 other it would be like an overdrive.  If the first gear is a bit lower in the 5 speed cluster then raising the gearbox sprocket by a tooth will make a big difference.  If you cannot increase the gearbox sprocket by a tooth then reducing the rear one by three teeth will have roughly the same affect.

Dave.

MGI

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Re: 5 speed Gearboxes - B series.
« Reply #7 on: 10 May, 2021, 07:46:17 »
I cannot do much about the rear sprocket as 42t is apparently the lowest available.Before I do anything expensive I have decided to ride it flat out in third & note the revs, then check the revs flat out in top, if there is a major discrepancy it may be that the bike is, in fact, overgeared. (This procedure will involve me finally installing the electronic tacho that I bought about a year ago prior to these ground breaking experiments taking place). The Nova touring gearbox does have a lower 1st and the gap between 2nd & 3rd is reduced.

Pete C

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Re: 5 speed Gearboxes - B series.
« Reply #8 on: 10 May, 2021, 10:18:04 »
I've never heard of a 5 speed box but I could be (and often am) wrong  ;D

The way we use these bikes now is a bit different to the way they were (ab)used when they were the only form of transport for a family.

Consequently I think they are a bit under geared and I have installed engine sprockets with a couple of extra teeth on both B31 and B33 bikes. It makes quite a difference on how busy the engine feels at that 55-60 mph range. Much cheaper than a set of gearbox internals - check out the 5 speed conversions for Triumphs and think how many beer tokens that represents! :'(

Just a couple of days before I saw this thread I'd been thinking my M33 could easily pull a higher ratio, but I like the relative simplicity of having just four gears to choose from. I like the idea of just raising the gearing instead, and I'd already thought that the bike would easily pull a 10% higher gear. That's even though the M33 is geared 5% higher already.

Pete, did you tend to cruise at a higher speed and/or find your mpg improved when you raised the gearing?


Afraid I never check my fuel consumption. Whatever it is I reckon it's still one of the cheapest ways of having fun.  ;D

I don't think it has really made any difference to cruising speed but the engine isn't as busy and it feels more relaxing.

DAVE BRADY

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Re: 5 speed Gearboxes - B series.
« Reply #9 on: 10 May, 2021, 11:35:22 »
Hi,

If you go up by too many teeth you will end up were 3rd will be faster than 4th because the engine can not pull the higher gear.  You may also find that the fuel consumption goes up as the engine is working harder to keep pulling the bike along.  The other thing to consider is that pulling away from a standstill and particularly on a hill will be harder on the engine and clutch. 
I can remember someone putting a 23 or possibly a 24 tooth engine sprocket on an A10.  Apparently it would cruise at 80 with comparatively low revs but needed quite a wide throttle opening to keep it there with resulting poor fuel consumption due to the inefficiency of the engine. 
Both my A65s and my wife's plunger 'Flash are one tooth up on the gearbox sprocket giving about 3500rpm at 60mph.

Dave,