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#657583 - 06/20/16 2:57 am Re: 1968 bsa a650 gearing [Re: COP242]  
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NickL Offline
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A lot depends on the state of tune of the engine as well.
The 21-47 set-up, on my OIF thing works well but i've ridden others that need to 'buzz' a bit more at 70, so 20-47 is more suitable.
I will state that my old one lung heap has had a few mods to improve mid-range ride-ability though.

Nick



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#657592 - 06/20/16 4:37 am Re: 1968 bsa a650 gearing [Re: COP242]  
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Andy Higham Online content
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Andy Higham  Online Content
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Bolton Lancs UK
You don't know what revs feel like until you hold a Villiers engine wide open at 11,500 RPM


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
Modified Nu-Trak GM500cc sprint/LSR bike "Deofol"
2003 Aprilia RSV Mille "Lo Stregone"
#657697 - 06/20/16 6:43 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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NickL Offline
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I raced a Norton Atlas engined outfit a few times, that is probably on a par.........



#662573 - 08/01/16 6:21 pm Re: 1968 bsa a650 gearing [Re: Allan Gill]  
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COP242 Offline
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Guys I installed a new tachometer on my bike today and checked I run 50 mph at 4000 rpm, I have a front 20 and rear 47 with a 18 inch wheel, any idea how I can get a little less rpm at 50 without changing the front sprocket ?

#662580 - 08/01/16 8:23 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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gavin eisler Online content
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argyll. scotland, uk
Maybe your clutch is slipping , with that gearing you should be doing more than 50, around 70.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#662581 - 08/01/16 8:32 pm Re: 1968 bsa a650 gearing [Re: Allan Gill]  
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COP242 Offline
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Originally Posted By Allan Gill
Unfortunately it's not always about 70mph cruising speed. Or what torque the motor can give. I've set my motor up to pull in a high gear (3rd or 4th) from 1500 rpm until it gets to the point where it revs out. Torque isn't an issue. That's with close ratio box and 19:42 gearing. It's great back home where I live and if touring then I can even go a tooth higher still. However the oil pump can not keep up at the lower revs (especially that low) and you eventually bugger something. One thing that I am seeing when doing the rallies is a lot of people rarely ride their bikes back home and the most use the bike gets is the 40-50 mph rides at rallies often not even seeing those speeds. And whilst that is fine, the gearing choice should be made to suit that purpose.
I also thought of that but it isn't

#662582 - 08/01/16 8:33 pm Re: 1968 bsa a650 gearing [Re: gavin eisler]  
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COP242 Offline
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Originally Posted By gavin eisler
Maybe your clutch is slipping , with that gearing you should be doing more than 50, around 70.
nope, I checked that

#662592 - 08/01/16 11:51 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Shane in Oz Online content
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Originally Posted By COP242
Guys I installed a new tachometer on my bike today and checked I run 50 mph at 4000 rpm, I have a front 20 and rear 47 with a 18 inch wheel, any idea how I can get a little less rpm at 50 without changing the front sprocket ?

What are the tachometer numbers (the fine print in the middle f the face near the bottom)?
It's possible that you have the wrong model fitted and it's reading high.

Standard gearing should give 50 mph at around 3000 rpm, and a bit over 60 mph at 4000 rpm

#662595 - 08/02/16 2:40 am Re: 1968 bsa a650 gearing [Re: COP242]  
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Allan Gill Offline
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Rotherham - S. Yorkshire
Change the back drum. But it will cost a lot of money.

Although I think your tacho isn't working right. If you have a 20 front, 47 rear, and the standard primary 28 crank and 58 clutch. Then you would be pulling 3500 at 50 and 4500 at 70 ( give or take 100 rpm)


beerchug
#662596 - 08/02/16 3:22 am Re: 1968 bsa a650 gearing [Re: COP242]  
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Nick Offline
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Out There!
Put a 21 on the front.

I put taller than stock gearing on my A65 (along with lower than stock compression) and love it! You can probably find a used front sprocket cheap.
Think I traded my rear hub for another model with a smaller sprocket. But if you can't do that, go 1 tooth bigger on the front.

Anyway, very happy with the performance. Still accelerates plenty hard but really booms down the freeway at speed - truly a joy to ride at highway speeds.


When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
#662599 - 08/02/16 5:53 am Re: 1968 bsa a650 gearing [Re: COP242]  
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gavin eisler Online content
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If your tacho is correct and your tooth counts are accurate, then either someone has changed the motor sprocket ( unlikely) or your clutch is slipping, the numbers dont add up at the moment.
As others have said,20/47 @ 4k = nearly 70. How did you test for clutch slip?


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#662602 - 08/02/16 7:07 am Re: 1968 bsa a650 gearing [Re: gavin eisler]  
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COP242 Offline
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Originally Posted By gavin eisler
If your tacho is correct and your tooth counts are accurate, then either someone has changed the motor sprocket ( unlikely) or your clutch is slipping, the numbers dont add up at the moment.
As others have said,20/47 @ 4k = nearly 70. How did you test for clutch slip?


would it make a difference the tach I have installed ? I put a regular voltage type tach on, I know most of these run off a cable, I could be wrong

#662605 - 08/02/16 7:19 am Re: 1968 bsa a650 gearing [Re: COP242]  
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Shane in Oz Online content
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Originally Posted By COP242
would it make a difference the tach I have installed ? I put a regular voltage type tach on, I know most of these run off a cable, I could be wrong

I was thinking of the original type Smiths cable driven tacho, and I'm sure Gavin was as well. Electronic units should be correct, but it might depend on how they're triggered. I assume it triggers off a coil wire.

Another possibility is that the speedo ratio is incorrect.
The speedo drive gearbox at the back wheel should have a ratio shown on it. Generally 2:1, 15/12 or 1.25:1.
Also the speedo number on the face (same fine print and spot as the Smiths tacho) includes the ratio, although it's rather cryptic. If you can post those numbers somebody should be able to tell you if it's correct.

#662609 - 08/02/16 8:20 am Re: 1968 bsa a650 gearing [Re: Shane in Oz]  
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COP242 Offline
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Originally Posted By Shane in Oz
Originally Posted By COP242
would it make a difference the tach I have installed ? I put a regular voltage type tach on, I know most of these run off a cable, I could be wrong

I was thinking of the original type Smiths cable driven tacho, and I'm sure Gavin was as well. Electronic units should be correct, but it might depend on how they're triggered. I assume it triggers off a coil wire.

Another possibility is that the speedo ratio is incorrect.
The speedo drive gearbox at the back wheel should have a ratio shown on it. Generally 2:1, 15/12 or 1.25:1.
Also the speedo number on the face (same fine print and spot as the Smiths tacho) includes the ratio, although it's rather cryptic. If you can post those numbers somebody should be able to tell you if it's correct.


I have checked with another bike along side and it reads the same speed as I do,

#662659 - 08/02/16 5:25 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Andy Higham Online content
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during the era these bikes were made there was an obsession with top speed. BSA would have geared the bike with the highest gearing it would pull. If your bike feels like it is revving high (without verification from a tacho) give it a big handful and you will find out how much more she has to offer. Speedway engines are big singles (and quite old fashioned in design)of around 75mm stroke, they are making power up to 12000 to 13000 rpm


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
Modified Nu-Trak GM500cc sprint/LSR bike "Deofol"
2003 Aprilia RSV Mille "Lo Stregone"
#662666 - 08/02/16 6:07 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Allan Gill Offline
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You mean it would have been geared to pull the best top speed with the highest gearing possible.

I believe this to be true, soon as the big port heads came out... So did the lower gearing. Early rocket models were geared at 20:42, I've run this gearing and with a torque'y motor it will pull it easily.


beerchug
#662701 - 08/03/16 12:09 am Re: 1968 bsa a650 gearing [Re: COP242]  
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Mark Z Online content
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I didn't read the whole thread, so I don't know if it's been stated if this is a Tbolt or a Lightning. Standard gearing for a Tbolt is 19-47, and for a Lightning, 20-47.

And, although the specified standard gearing for a Lightning is 20-47, I noticed back in the '70s that many Lightnings sold in the U.S. had 19-47, so you should count the teeth on your gearbox sprocket.

My 2 cents on gearing: I tried 21-47 and found that it was good on the interstate, but too high for many of the smaller hilly and curvy roads I ride on. I'm running 20-47 now and I find it suitable for both.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
#662704 - 08/03/16 1:24 am Re: 1968 bsa a650 gearing [Re: COP242]  
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Allan Gill Offline
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You must have different parts books. All the British one's state 20:47 on post 66 bikes. (With exception of Royal star and some years of firebird)

Those with small port/valve heads happened to be listed with 19:42 (which is a gnats tit taller than 21:47) or 20:42 as on the rocket model ( which with its spec was as good as calling it the early thunderbolt)


beerchug
#662716 - 08/03/16 4:37 am Re: 1968 bsa a650 gearing [Re: COP242]  
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NickL Offline
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I like the 21-47 gearing on my old heap, it keeps me frightened.



#662723 - 08/03/16 5:53 am Re: 1968 bsa a650 gearing [Re: Allan Gill]  
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Rich B Online happy
Rich B  Online Happy



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Stone Creek OH USA
Allan,

I've tried 20:42......seriously fun gearing, seriously useless gearing in the real world. That combination is just too tall to be used on public roads. But it is a lot of fun.

Riding style ultimately affects final gearing choices.

If you have the parts, IMO, the 19:42 is the best all around ratio for an A65 ridden on public roads. This may be a bit fast for some people and finding all of the brake drum bits can be difficult for some people.

21:47 is very close to 19:42 in ratio, but to me, just doesn't seem to be as much of a sweet spot. But just could be my perception. This combination is much easier to find the pieces to install for most people.

20:47 seems to work well for a lot of people. I really believe this is difference in riding styles or preference. For me, it doesn't work.

Then you get into A50's and sidecar gearing......not going there.........


Life is too short to drink cheap, bad beer.
#662725 - 08/03/16 6:29 am Re: 1968 bsa a650 gearing [Re: COP242]  
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COP242 Offline
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Is it hard on the a65 running it at 4000 rpms ?

#662726 - 08/03/16 6:50 am Re: 1968 bsa a650 gearing [Re: COP242]  
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gavin eisler Online content
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4 K- 5K is pretty much the sweet spot. max revs is 7K plus. the A65 likes to rev.
Whats hard is lugging the motor at low revs, these are not long stroke slow revving HD type motors.
At low revs, the plain brg big ends can suffer from lack of oil pressure if lugged up a hill.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#662747 - 08/03/16 10:56 am Re: 1968 bsa a650 gearing [Re: gavin eisler]  
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COP242 Offline
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Originally Posted By gavin eisler
4 K- 5K is pretty much the sweet spot. max revs is 7K plus. the A65 likes to rev.
Whats hard is lugging the motor at low revs, these are not long stroke slow revving HD type motors.
At low revs, the plain brg big ends can suffer from lack of oil pressure if lugged up a hill.




thanks again

#703514 - 08/01/17 12:13 am Re: 1968 bsa a650 gearing [Re: COP242]  
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I've been riding my restored 66' Lightning for a couple years now, thought it would be nice to have a little taller gearing so did a search and found this thread. From what I am learning from this thread is that I don't need taller gearing but I need to get used to the higher RPM's. So on my last ride I was cruising 45mph roads in 3rd gear rather than 4th. That put me closer to 3.5-4k, seems to be okay until things start vibrating loose I guess. 2.5-3k is smoother on my bike but will start running it at higher RPM. I guess I've been babying it and learned something. Is there danger in reving up to 7k or will it just rev itself out around 7k? I've reved up to 6k but sometimes in 2nd it pops out of gear.

#703551 - 08/01/17 11:12 am Re: 1968 bsa a650 gearing [Re: COP242]  
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gavin eisler Online content
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I seldom see 7 k rpm with my A65, generally changing up at 5.5 -6 k results in good acceleration. With std gearing there is a big gap between 2nd and 3rd, to catch the cam in 3rd means more revs in 2nd. My motor is most prone to pinking around 3 k , i am careful to be over this when charging a hill.
The factory rev limit was 7,250 rpms, racers go to 8 k, on the road 6.5 is a good safe maximum, ultimately the state of your valve gear limits the max ceiling, valve bounce with tired springs will lower this ceiling.Much of this depends on the riders perception of vibration,/ noise, my motor has a sweet spot from 4- 5.5 K, and spends most times in that band, racers who spend there lives at the top end of the rev band use a different crank balance factor to move the sweet spot up the range ( and will strip check motors after 10s of running hours, not thousands of miles). The 4 - 5.5 range is somewhere around peak torque, the oil pressure is good and the motor is very happy at these speeds, beyond 5.5 K , everything is working a lot harder , vibes and forces go up rapidly as do parasitic friction losses.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
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