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#710205 - 10/01/17 10:56 pm Layshaft end float  
Joined: Mar 2006
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htown Online content
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htown  Online Content
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Magnolia, TX
My 70 Thunderbolt refuses to shift into 3rd and 4th gear. I've turned the eccentric on the spring every way possible with no improvement. I've decided to start taking the gearbox apart to see if I can find the problem. I've looked at a lot of threads on the subject on gearbox issues and most mention checking the layshaft for end float. Can some one please explain how to do this? Also, how much of the primary needs to come apart to pull the gear cluster? I just recently redid the clutch and it isn't giving any problems.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
2-1974 Norton Commandos
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.
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#710211 - 10/02/17 12:02 am Re: Layshaft end float [Re: htown]  
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gavin eisler Online content
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gavin eisler  Online Content
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argyll. scotland, uk
The clutch centre must be removed , so all the primary , sorry ,there is no other way..but read on , you might not need to.
Thats the bad news, the good news is that once the clutch is out of the way, the gearbox sprocket and sleeve gear can remain in situ, although it would be a good time to fit a new sprocket if needed. With the clutch centre removed, Undo the 5 x 5/16" nuts on the trap door and the whole lot will slide out, maybe need to waggle the cam plate a bit , it wont pull free if this is at one end of the travel, But hang fire, check some other stuff first before going radge on the primary and stripping the whole lot.

You will need a clock gauge , or lead wire and a micrometer to measure the end float.

Before you strip the primary , pull the inner case TS ( remember to pull the tach drive before destroying the inner and careful when pulling the inner , dont want to disturb the idler pinion and lose the valve timing,), make sure the Main shaft nut which secures the kickstart ratchet is tight, if this has backed off at all ,all sorts of weird things can happen. its also worth checking all the bits of the ratchet mech are present, if a thrust washer is missing from behind the spring, more weird stuff happens even if the nut was tight. DAMHIK. If you are lucky that might be all it is, no need to pull the primary for this .

Once the timing side inner case is removed, the lay shaft end is exposed, push pull axially on this , the optimum end float is 0.003 " , which is "just perceptible", A clock gauge can be mounted to measure the true axial end float, if not available you can use "leads £ and a micrometer, ( now its time to strip the primary) once stripped the lay shaft, thrust washers and gears plus a ring of soft solder or ideally lead wire can be assembled ( no need for the MS at this point, just layshaft with gears and leads on DS end mounted in trapdoor and refitted to case) , crush the solder by nipping up the trap door , strip then mic the solder/lead to get max end float , subtract 4 thou ( 4 because the casing surface will not be even) and thats the thrust washer you need. The thrust washer which sets end float is on the drive side of the Layshaft , this could be left out if using the lead to measure the gap. Compare the two.
Three sizes of thrust washer used to be available, usually the max of the three is needed,alternatively an over thick thrust washer can be lapped to size on a diamond sharpening stone , laborious , but easy low tech for the average joe.
Thats a lot of words,
More simply, the new thrust washer is the total endloat , minus 4 thou, to give about 3 thou when assembled.

Its sometimes easier just to fit a few shims you have lying around, you dont even need to measure anything for this, just trial and error untill "just perceptible", then make a thrust washer the thickness of the test shims.

Hot tip. A scrap piece of corrugated iron ( wriggly tin) makes a very useful parts holder, put MS and parts in one groove, lay shaft bits in the other.

refusing to shift into 3rd, hmm, suspect chipped selector pawls, new pawls and springs are not a budget breaker, of course it could be a few other things,
I have played with these boxes a fair bit, if you cant get 3rd it usually means that the change to 2nd was incomplete ,usually because the gear lever has not returned far enough to reset the selector pawls into the fresh plate windows, if the extreme ends of the spring adjustment bring no change then its probably something further in. The selector pawls are easy to check before pulling the box any further apart.

Badly gouged cam plates and mashed plate index plungers are common, bent selector fork maybe. You wont know until you pull the cluster
One useful feature of this box ( if std ratios are used ) is that the sliding gears are the same, which allows you to swap them from MS to LS , this puts the previously unworn side of the engagement dogs into play, you will need a press to do this. Somewhere out in the ether is a wonderfully detailed write up by Ed V on how to set up and shim an A65 box, but for most folk getting the LS end float set correctly will give very good results.

There are other things that help, polishing around the cam plate selector fork track cheeks gives a slicker shift, likewise polishing the inner faces of the cam plate fork tracks, the cam plate is a pretty crude stamping , its not hard to improve its function.

Last edited by gavin eisler; 10/02/17 12:32 am.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#710227 - 10/02/17 2:54 am Re: Layshaft end float [Re: htown]  
Joined: Mar 2006
Posts: 1,164
htown Online content
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htown  Online Content
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Magnolia, TX
Thanks for the in-depth write up Gavin,
Got a dial indicator(clock) gauge. No tach drive she's a Thunderbolt.
Will post more in a few days when I can get her up on the lift.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
2-1974 Norton Commandos
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.
#710256 - 10/02/17 11:04 am Re: Layshaft end float [Re: htown]  
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gavin eisler Online content
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argyll. scotland, uk
nae bother, lets hope its the MS nut, the fact that its 3rd 4th thats missing suggests it might be that easy , 1st to 2nd happens on the LS


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#710333 - 10/02/17 9:32 pm Re: Layshaft end float [Re: htown]  
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I have some shims here.... if you need a certain thickness call me as they can vary.

#710543 - 10/04/17 10:12 pm Re: Layshaft end float [Re: htown]  
Joined: Mar 2006
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htown Online content
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htown  Online Content
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Magnolia, TX
Tried hand shifting the cam plate and it absolutely won't go into 3rd or 4th. Feels like something is completely bound up.
Measured the float on the layshaft, .015, so that will need fixed.
Have everything stripped except removing the clutch hub. The threads on my puller are in bad shape and I don't want to damage the hub.
Have to wait a few days for a new one to come in the mail.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
2-1974 Norton Commandos
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.
#714147 - 11/07/17 2:23 am Re: Layshaft end float [Re: htown]  
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htown Online content
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Magnolia, TX
Okay, I have had everything apart and now it's back together, Here's what I did to it
new cam plate
new plunger
new plunger spring, cut 2 coils off
new nos shifter pawls
new shifter return spring with eccentric hat (70 model type)
switched the layshaft 3rd with the mainshaft 2nd,
new layshaft ds shim that brought the play to around 3-4 thou
polished everything per Gavins writeup.
everything seemed to dry shift okay when turning the quadrant before fitting the inner timing cover window.
However, first road test and it refused to reliably shift up from 2nd to 3rd. Did once or twice out of maybe 20 attempts. Just stayed in second gear.
When lifting up the shift lever it just felt like it wasn't connected to anything. Like only the lever was moving and it wasn't engaging anything.
I understand setting the bias correctly on the shifter spring eccentric is important on these boxes.
The eccentric hat has two notches. Right now I have the fat part of the eccentric to the rear with the notches close to horizontal.
If I'm thinking about this right because I'm not able to upshift I need to increase the pressure on the the upper spring arm so it returns the selector shaft better.
Do I turn the fat part of the eccentric so that it is facing down and the notches are vertical?
What a frustrating setup to deal with. Disassemble, tweak, reassemble, road test , repeat.

Last edited by htown; 11/07/17 2:25 am.

1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
2-1974 Norton Commandos
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.
#714153 - 11/07/17 2:55 am Re: Layshaft end float [Re: htown]  
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NickL Online content
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Aus
Setting the spring bias up can be a pain, the granny's tooth sometimes has to be fettled a little too.



#714154 - 11/07/17 3:04 am Re: Layshaft end float [Re: htown]  
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Mark Z Online content
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Mark Z  Online Content
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Owego, NY, USA
At the risk of stating the obvious: Are you absolutely sure there's no movement between the shift lever and the quadrant shaft?
If not, make a scribe mark across both and push the lever up and down firmly with your hand, observing the marks closely.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
#714169 - 11/07/17 7:52 am Re: Layshaft end float [Re: htown]  
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leon bee Offline
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arkansas
Last time, I actually took a hole saw to a ragged cover so I could road test and turn that dam thing without disassembling. I hate that setup.

#714179 - 11/07/17 2:50 pm Re: Layshaft end float [Re: htown]  
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gavin eisler Online content
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argyll. scotland, uk
, The upper arm of the spring needs more downward pressure to complete the shift to second and reset the pawls, ,I think turning the top hat so fat part is at 6 oclock will do it, leave off the outer cover and kicker, temp fit gear lever and test, sometimes it will overcompensate and the change will mess up on a down shift, find the sweet spot then box up. When I do this I dont think it through, i just move it one way or the other its a 50 / 50 shot. Checking selection by moving the rear wheel gives a fair test , but on the road is what matters, A bump start with no kicker can save a lbit of faffing around if the setting needs tweaked after a run through the gears on the road.

Last edited by gavin eisler; 11/07/17 5:06 pm. Reason: &0 on needs outer cover for clutch op.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#714253 - 11/08/17 4:18 am Re: Layshaft end float [Re: htown]  
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htown Online content
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Magnolia, TX
Success. I was about ready to set the dang thing on fire. I fiddled that eccentric around every which way and I still couldn't get 3rd and 4th. Finally I took the new eccentric cup, spring and toothed piece off and put the old original parts back on. Dry shifted better and when I rode tested it went up and down the gears without a hitch. For whatever reason the original parts were what it needed. I had replaced them because I thought they were a pretty worn. But apparently something in the new ones were a little off. Also, the original cup has the hole directly in center so no way to bias, but as I said it works so I'm happy.
I'm sure replacing the worn camplate, plunger and pawl along with the polishing and setting the layshaft play will help make a better box overall.
Thanks Gavin for continuing to post the info on BSA boxes. I really appreciate it. I know posting on these forums can be pretty frustrating sometimes. I think its time we cut our losses with a certain poster on the Triumph forum. I intend to go no farther. He used to be on there years ago and it was the same endless rabbit tracks. Good point he is capable of hurting himself or destroying his bike.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
2-1974 Norton Commandos
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.
#714271 - 11/08/17 2:51 pm Re: Layshaft end float [Re: htown]  
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gavin eisler Online content
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argyll. scotland, uk
hurray! Hopefully all will be slicker than before, strange that the eccentric top hat isnt eccentric, not the forst time this has come up, maybe thats a subtle change from 70 to 71?
I know what you mean about the certain poster, maybe he will get his bike going without damage to himself or the machine, I hope so.
just for the records sake , what were the most worn components, I am guessing camplate and plunger?

Last edited by gavin eisler; 11/08/17 10:10 pm.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#714360 - 11/09/17 10:19 am Re: Layshaft end float [Re: gavin eisler]  
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Lekkie Offline
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Quote
Finally I took the new eccentric cup, spring and toothed piece off and put the old original parts back on. Dry shifted better and when I rode tested it went up and down the gears without a hitch. For whatever reason the original parts were what it needed. I had replaced them because I thought they were a pretty worn. But apparently something in the new ones were a little off. Also, the original cup has the hole directly in center so no way to bias, but as I said it works so I'm happy.
That is very interesting. I too had a similar problem with an A10 gear box. The "claw" selector was worn so I replaced it and the return spring and what happened after doing this was that after selecting a gear the shift pedal would not return to the center position. I never did resolve that problem until I refitted the original worn parts and then everything worked just fine! All very strange.

#714421 - 11/09/17 10:33 pm Re: Layshaft end float [Re: htown]  
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htown Online content
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htown  Online Content
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Magnolia, TX
Better, often the enemy of good.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
2-1974 Norton Commandos
2004 XL 1200R Sportster

Everything will be alright in the end. If its not alright, its not the end.

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