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#656573 - 06/12/16 1:23 pm 1968 bsa a650 gearing  
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COP242 Offline
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Just wondering what everyone is running for gears, I find my bike is revving at slow speed, like to change my rear sprocket but not sure what to.

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#656575 - 06/12/16 1:39 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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gavin eisler Online content
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argyll. scotland, uk
Rear sprocket is not an easy change, check your gearbox sprocket teeth, 19 lowish, 20 stock, 21 easy cruising less snappy acceleration, one on the front is worth 3 off the rear.
Stock 68 has 20 t front 47 rear ( FS had a 51 rear option. Not heard of smaller rear options.
I use the 21 front and 47 option ( my motor is a 750 and pulls this easily). A 22 can be fitted but it means splitting the cases.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#656578 - 06/12/16 1:53 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Allan Gill Offline
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What year is the bike?

42t drums are available. I run 18:42 however my clutch is like running the bikes as 19:42 ( which is a fraction taller than 21:47)

If your running a conical hub the min is 47

If your running a post 66 bike then your will need new 2 part spindle, different bearing, brake plate, and other parts to make the bike use a 42t drum. Cost me about £200 to change it.

If you have a pre 66 bike or one which already has the steel (chromed?) brake plate then you can switch between a 42t drum or the optional drum without the integral sprocket. But you can only use the drum designed for the steel brake plate.

Hope that makes sense


beerchug
#656579 - 06/12/16 1:58 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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What RPMs are you seeing and at what speeds? I see you are a new member, are you also new to Brit bikes? These aren't like Harleys, they need to rev a bit to be happy.


When given the choice between two evils I picked the one I haven't tried before
#656580 - 06/12/16 1:59 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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I agree, check the front sprocket- there has always been about 5 sizes available. Kinda hard to do.....what I do is, with the bike lifted or on centerstand, reach up there with a stick with some white paint on the end and mark one tooth. Maybe clean that tooth a bit first, paint will stay on long enough to turn wheel and count teeth. Count them more than once to be sure.

Like Gavin said, unless you have an oversize rear sprocket you're kinda locked in on the rear.

#656590 - 06/12/16 2:35 pm Re: 1968 bsa a650 gearing [Re: Allan Gill]  
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COP242 Offline
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1968 bsa 650

#656591 - 06/12/16 2:37 pm Re: 1968 bsa a650 gearing [Re: shel]  
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at 50 mph it sounds like it is really revving, I'm not sure about rpms I don't have a tech, just seems high, you maybe correct

#656604 - 06/12/16 3:58 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Allan Gill Offline
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Standard gearing for that bike (20:47) would be 3500 rooms at 50mph.

21:47 - 3000rpm
19:47- 4000rpm


beerchug
#656622 - 06/12/16 5:47 pm Re: 1968 bsa a650 gearing [Re: Allan Gill]  
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it does have standard gearing but at 50mph it sounds like it's going to blow, lol

#656623 - 06/12/16 5:47 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Originally Posted By COP242
it does have standard gearing but at 50mph it sounds like it's going to blow, lol


Earplugs.

50 mph/3,500 rpm isn't much over minimum top gear speed.

Last edited by triton thrasher; 06/12/16 5:50 pm.

Amateur Loctite enthusiast.
#656627 - 06/12/16 7:14 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Allan Gill Offline
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You get used to it, when you get to 7000+ it's gets more interesting wink

Worst part is when you jump on a jap multi and open it up, and they don't come on cam till they get to 8000 rpm. Until that point they sound like a child screaming.


beerchug
#656629 - 06/12/16 7:30 pm Re: 1968 bsa a650 gearing [Re: Allan Gill]  
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LOL guys, what would dropping the rear sprocket 1 or 2 teethe do

#656634 - 06/12/16 8:19 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Originally Posted By COP242
LOL guys, what would dropping the rear sprocket 1 or 2 teethe do


You can't drop the rear sprocket one or two teeth. You probably have a 47 tooth now; you can replace it with a 42 tooth. There aren't any intermediate sizes, unless you do a lot of machine work to modify one from another model.

Your bike was designed to run with either a 19, 20, or 21 tooth on the front (depending on what it was to be used for) and a 47 tooth on the back. You could also get a 17 tooth (for pulling a sidecar) or 18 tooth (for racing) but you wouldn't use these on a normal bike.

With a 20 in front and a 47 in the rear, the bike will be turning about < 4000 RPM at 60 MPH, which is right where it wants to be for efficient and effective running.

I've been riding (and watching other people ride) 500 and 650 BSAs since 1974. It's my opinion (just MY opinion) that more BSA engines have been destroyed by people "lugging" them, running them too slow, than for any other reason.

The basic reason was that, back in the day, very many people bought BSAs because they wanted to emulate the Big Man Bikes, the Harley Davidsons. Harleys were DESIGNED to "chug" at 2500 RPM, and would effectively pull hard from that RPM.

You WILL destroy a BSA engine trying to do that. But everyone from your Uncle Bill, to "Chopper" magazine, thought that BSA (and cousin Triumph) engines were "meant" to run like Harleys, yeah boy, she'll chug and pull like a freight train, that BSA, don't want to rev her too high buddy, and don't touch that front brake, she'll throw you over the bars etc etc etc and other nonsense.

No reason in the world not to use one of the three standard gearing sets on your bike. UNLESS the clutch is slipping continuously (and it won't do that for long), your BSA engine SHOULD run in the 3500 - 4000 RPM range, and will run 4500 - 5000 all day long. That's what it's designed for ....

Lannis



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#656648 - 06/12/16 10:21 pm Re: 1968 bsa a650 gearing [Re: Lannis]  
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Wot 'e said.

Harleys have roller bearings in the big end. These work well at lower speeds but the rollers skid at higher speeds and wear the crankpin and con rod bearing race.

British parallel twins have plain big end bearings which rely on a cushion of oil to prevent metal to metal contact and hence wear. That needs engine speeds to be kept up to maintain oil pressure, and also keeps the oil film distributed more evenly around the bearing.

#656675 - 06/13/16 5:16 am Re: 1968 bsa a650 gearing [Re: Lannis]  
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THANKS LANNIS

#656793 - 06/13/16 11:16 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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The normal and best way to gear your bike is to the speed you spend most time riding at.

Every engine will have a "sweet spot".
This is the particular engine speed where the vibrations from the engine are at the least.
You gear your bike so the speeds you ride at most times fall into this least vibration range.

No two bikes are identical so what is right for one will not necessarily be right for you.
I spent years riding a low revving high geared A 10 and a hig geared WD B 40.
When I got the A 65 I geared it up way too high.
Thus it is sitting in the shed waiting for a complete bottom end rebuild.


Bike Beesa
Trevor
#656843 - 06/14/16 10:22 am Re: 1968 bsa a650 gearing [Re: BSA_WM20]  
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Originally Posted By BSA_WM20
The normal and best way to gear your bike is to the speed you spend most time riding at.

Every engine will have a "sweet spot".
This is the particular engine speed where the vibrations from the engine are at the least.
You gear your bike so the speeds you ride at most times fall into this least vibration range.



That's good advice right there ....

Lannis


"To learn who rules over you, simply find out who you are not allowed to criticize."
Voltaire
#656846 - 06/14/16 10:38 am Re: 1968 bsa a650 gearing [Re: COP242]  
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I think a slight adaptation to that might be more apropriate. Gear it so that your preferred highway speed is at the most comfortable spot between 4000-5000 rpm

Just to stop people gearing the bike to be doing 70 at 3000 rpm.


beerchug
#656854 - 06/14/16 11:11 am Re: 1968 bsa a650 gearing [Re: Allan Gill]  
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Originally Posted By Allan Gill
I think a slight adaptation to that might be more apropriate. Gear it so that your preferred highway speed is at the most comfortable spot between 4000-5000 rpm

Just to stop people gearing the bike to be doing 70 at 3000 rpm.


I agree, but in order to interpret "Least Vibration", you have to apply some "mechanical sympathy" to that.

Anyone with a developed sense of "mechanical sympathy" will recognize the pain that the BSA engine is going through when it is asked to pull hard at 3000 RPM. It may not have any "higher frequency" vibration, but it is obviously being tortured .... whereas even though there might be a slight "buzz" at 4K RPM, the motor is "happy" there.

My M21 is a good example. At an indicated 48 MPH, it drops into a "zone" where it will obviously run from here to the moon with excellent gas mileage and no strain on the engine. It'll go faster or slower, but isn't as "happy" there ....

Lannis


"To learn who rules over you, simply find out who you are not allowed to criticize."
Voltaire
#656924 - 06/14/16 10:12 pm Re: 1968 bsa a650 gearing [Re: Shane in Oz]  
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Originally Posted By Shane in Oz
Wot 'e said.

Harleys have roller bearings in the big end. These work well at lower speeds but the rollers skid at higher speeds and wear the crankpin and con rod bearing race.

British parallel twins have plain big end bearings which rely on a cushion of oil to prevent metal to metal contact and hence wear. That needs engine speeds to be kept up to maintain oil pressure, and also keeps the oil film distributed more evenly around the bearing.


HD is also a much longer stroke engine. A10s and Triumph 650s are also of longer stroke than the A65, which is over-square (bore bigger than stroke). Long stroke engines tend to be torque-ier at low rpms (more leverage on the crank), but more rpm-limited because of the greater piston travel. Short stroke engines, generally speaking, develop their power in higher rpm ranges.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
#657361 - 06/18/16 7:08 am Re: 1968 bsa a650 gearing [Re: Lannis]  
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Originally Posted By Lannis


I agree, but in order to interpret "Least Vibration", you have to apply some "mechanical sympathy" to that.

Anyone with a developed sense of "mechanical sympathy" will recognize the pain that the BSA engine is going through when it is asked to pull hard at 3000 RPM. It may not have any "higher frequency" vibration, but it is obviously being tortured .... whereas even though there might be a slight "buzz" at 4K RPM, the motor is "happy" there.

My M21 is a good example. At an indicated 48 MPH, it drops into a "zone" where it will obviously run from here to the moon with excellent gas mileage and no strain on the engine. It'll go faster or slower, but isn't as "happy" there ....

Lannis


Yes, sympathy for your engine.
I always was poking fun at the Notrun owners because their Notruns were always blowing up then a good friend pointe out the reason.
The isolastics, on the rare occasions when they were set up properly isolated the rider from the "one more second at this speed buster & I am going to toss a rod" sort of vibrations that we owners of rigidly monted engines are all familiar with.


Bike Beesa
Trevor
#657453 - 06/19/16 4:33 am Re: 1968 bsa a650 gearing [Re: COP242]  
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John Alexander Online content
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As a rule of thumb 4,000 revs at 70 MPH would be the gearing to aim for, similar to standard gearing on the 650 triumph,4000 revs at 60 MPH is far too low.
Goldie John.

#657456 - 06/19/16 5:18 am Re: 1968 bsa a650 gearing [Re: John Alexander]  
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Originally Posted By John Alexander
As a rule of thumb 4,000 revs at 70 MPH would be the gearing to aim for, similar to standard gearing on the 650 triumph,4000 revs at 60 MPH is far too low.
Goldie John.

Not on an A65 it isn't.
4,000 rpm at 100 km/hr is about right for a BSA unit twin, so around 4,400 at 110 (70 mph).
You have to keep an A65 over 3500 in top with any sort of load on th engine.

Your gearing works well for a T140 or an A10.

#657479 - 06/19/16 11:36 am Re: 1968 bsa a650 gearing [Re: COP242]  
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Standard gearing on a BSA A 65L, at 5,000 revs should be aprox 80 MPH. For comfortable cruising, revs are best kept below 4,500 revs for any sustainable distance, fact of life, this is the limitation of the parallel twin hence the eventual dominance of high performance Japanese motorcycles in the late 1960s.Sports riders on british iron would have at times to replace tappet covers, screw on chrome air filters, fractured mudguard stays, leaking central bolt housing petrol tanks, not to mention rotating speedo/rev counter heads and blown bulbs. Be on the safe side ,keep the revs down, but the speed up. British bikes, i love them to death, they have engines , the Japanese have motors. Nuff said.
Goldie John.

#657579 - 06/20/16 2:05 am Re: 1968 bsa a650 gearing [Re: COP242]  
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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.


beerchug
#657583 - 06/20/16 2:57 am Re: 1968 bsa a650 gearing [Re: COP242]  
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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



#657592 - 06/20/16 4:37 am Re: 1968 bsa a650 gearing [Re: COP242]  
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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"
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#657697 - 06/20/16 6:43 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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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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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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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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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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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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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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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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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 Offline
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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 Online content
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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
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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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argyll. scotland, uk
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
#703652 - 08/02/17 2:37 am Re: 1968 bsa a650 gearing [Re: COP242]  
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Mark Z Online content
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I ran without gauges on either of my A65s for...oh, around forty years. And then I got me an electronic tacho (which, I'm sorry to say, is no longer working - GPS speedo soon to come though). But having the tach work for a little while allowed me to do some benchmarking. Now I can go back to "what feels right".

My riding is a combination of 15 miles to and from work, mostly on an interstate, where the average speed travelled is 70 mph, and on the surrounding secondary highways and rural roads, where speed varies from 45 to 60 mph. I have 20-47 gearing, and Mikuni VM32 carbs (FWIW, because I'm going to include throttle openings). Whenever I go on "outings", I stay off the interstates and stick to the secondary highways, which I find more pleasurable.

On the interstates, I find I have to kind of "work at" maintaining 70 mph (4400 rpm), especially if it's windy, whereas 65 (4100 rpm) feels like an easier gate, requires no effort and has better throttle response. With the MIKS, with no wind, 65 mph is about 3/8 throttle, and 70 mph is about 1/2. Don't get me wrong; the engine runs strong at 4400 rpm and will go way faster; I'm just talking about what's comfortable. I don't know if it's me or the bike, but like I said above, I'm going back to what feels right, and getting over the stigma of being passed by Smart cars.

Riding on secondary highways, the A65 (and I) will run happily at 55 (3500 rpm) to 60 (3800 rpm) all day long without breathing hard. I've also been staying in 3rd gear more on the back roads - this way I can just use the throttle to speed up and slow down for curves without shifting or braking. You just don't reach maximum speed on the straights, but oh well, for me at least, it's not always a race.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
#703666 - 08/02/17 8:18 am Re: 1968 bsa a650 gearing [Re: COP242]  
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gunner Online content
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When I first built my A65 Firebird, I was using 19/47 sprockets and found the bike would accelerate very well, however when cruising at on the highway at a steady 60mph, the engine seemed to be revving more than I expected. I don't have a tacho fitted so couldn't tell you what revs I was doing.

Subsequently I decided to fit a 21 tooth gearbox sprocket. It was a few hours work removing the primary cover, clutch etc to get to the sprocket and if I remember correctly the new sprocket only just fits through the hole on the inner cover. I think I read somewhere that to get a 22 tooth sprocket to fit, the hole can be filed to clear the teeth, so no need to split the cases, maybe someone can confirm.

Back on the road with the new 21/47 sprockets, I found the acceleration not quite as good and the 60mph cruising was a bit more relaxed, the revs having been reduced by a few hundred so was a worthwhile mod.

The engine still feels buzzy and I guess this is just the way A65's are, nevertheless I wouldn't mind trying a 22 tooth sprocket to see how that feels.

One of the issues with raising the gearing is that take-offs in first gear need more clutch slip and riding around town means you're almost always in 1st or 2nd.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
#703700 - 08/02/17 6:11 pm Re: 1968 bsa a650 gearing [Re: gunner]  
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Lannis Online content
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Central Virginia
Originally Posted by gunner
When I first built my A65 Firebird, I was using 19/47 sprockets and found the bike would accelerate very well, however when cruising at on the highway at a steady 60mph, the engine seemed to be revving more than I expected. I don't have a tacho fitted so couldn't tell you what revs I was doing.

Subsequently I decided to fit a 21 tooth gearbox sprocket. It was a few hours work removing the primary cover, clutch etc to get to the sprocket and if I remember correctly the new sprocket only just fits through the hole on the inner cover. I think I read somewhere that to get a 22 tooth sprocket to fit, the hole can be filed to clear the teeth, so no need to split the cases, maybe someone can confirm.

Back on the road with the new 21/47 sprockets, I found the acceleration not quite as good and the 60mph cruising was a bit more relaxed, the revs having been reduced by a few hundred so was a worthwhile mod.

The engine still feels buzzy and I guess this is just the way A65's are, nevertheless I wouldn't mind trying a 22 tooth sprocket to see how that feels.

One of the issues with raising the gearing is that take-offs in first gear need more clutch slip and riding around town means you're almost always in 1st or 2nd.


Yep, exactly my experience with my '69 Firebird. You are correct in that a 21 tooth fits through the inner primary as is ... a 22 tooth would need some machine work (or a lot of handwork) to fit.

Me personal, I wouldn't go higher than a 21. Sometimes I think 21 might be a little too high, although it's the way I've been riding it for a long time. With 21 teeth on the front sprocket, I'm almost to 70 MPH before the bike is at 4000 RPMs, and at 60 MPH it's at 3400 or so. With an engine that is literally lugging at 3000 RPM under load (despite how bad some people wish it would chug like a V-twin), you have to manage it carefully to make sure you don't ruin it with that gearing.

I found that getting the crank dynamically balanced and installing an EI made the biggest difference in smoothness. Lowering cruising RPM can only go so far .....

Lannis


"To learn who rules over you, simply find out who you are not allowed to criticize."
Voltaire
#703735 - 08/02/17 10:58 pm Re: 1968 bsa a650 gearing [Re: COP242]  
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Allan Gill Offline
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I'm another one that started with 19:47, then switched to 21:47 (now on 19:42 we'll close)

21:47 is the most you want to run on a stock bike. I used to run a thunderbolt that had 22:47, it would go some too but there was a lot of clutch slip setting off, which resulted In a lot Of clutch issues. When I attended the Danish Rally i was running 20:42 which is a tad taller still with a close ratio box. My bike was setup to give a lot of torque at lower revs so it worked ok, it would cruise at 75 all day long but on the ride outs where the runs are slower it wasn't much fun. So I dropped to 19:42 and returned to the standard gearbox. Still running a small port head... and that makes a big difference in tractability.


beerchug
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