BSA to NORTON CONVERSION

[Goldie]

I have just purchased a 350 Gold Star with RRT2 gearbox and is fitted with a Norton clutch.

Can anyone tell me if the splined end of a Norton Domminator gearbox mainshaft is the same size as a BSA gearbox mainshaft.

I have reason to believe that a standard Norton clutch has been fitted directly on to the BSA shaft, hence the slight movement of the clutch spider(centre) on the shaft which is causing slight runout and vibration.

If the BSA shaft is slightly smaller, is there a manufacturer who makes a BSA to Norton spider conversion so i can get a nice snug fit?

[33d6]

It is very possible you merely have slight wear between the components. This type of wear usually worsens rapidly once it starts. This type of conversion was a common thing to do in it's time. There is nothing inherently wrong with it.
It is probably not a matter of replacing just one component if the other is equally worn.
There are several quite simple methods of repair, using the appropriate grade of Loctite for example but from your hesitation about the problem I suspect this is not an area you are familiar with. I would strongly suggest you get a competent person to look at it. You may get a happy answer.
The worst thing you can do is let your mate have a go at it. (We've all got a mate who thinks he knows what to do but stuffs it completely, I make a steady amount of pocket money fixing up this type of stuff up.)
Good luck,

[Goldie]

Thanks for your advice and info.
I have now found out that to use a Norton clutch on a BSA RRT2 gearbox, it must have had a BSA A7 plunger mainshaft fitted, which has a splined end the same size as a Norton mainshaft.
I have the measurements of the spline on a new Norton shaft taken from a Haynes manual, but unfortunatly do not have the measurements of the A7 plunger shaft, just to make sure that they are identical in size.

I am reluctant to use Loktite 648 which has been reccommended to take up the slack, as it could be a very hard task to dismantle, even with the use of heat.

I would be very grateful if anyone could give me the OD diameter of the spline on a A7 plunger shaft, so i could then measure the shaft in the bike, before shelling out over £100 for a new shaft if needed

[douglas]

It will most likely your clutch centre spider that has hammered out, which gets worse over time. I'm looking for a new one at the moment. Remember the shaft will be way harder than the spider. I've fitted a Norton clutch to a Burman box and have the same problem. If you find a source for a new spider please inform me, cheers!  Douglas

[33d6]

Measuring the splines is not as straightforward as you think. Any dimension given in a Haynes manual will only be nominal. Nothing is made to an absolute size, in their day the factory would have a tiny plus or minus allowance for each part and a certain amount of hand fitting and selective assembly was to be expected.
Even if you can find another shaft it is liable to be as old and worn as the one you have.
If the movement is so slight that Loctite will take it up then there is little to be gained from secondhand replacement parts. Stripping down Loctited parts is easy if you have the right tools so don't worry about that.
As far as your clutch runout and vibration is concerned I would be checking the condition of the clutch bearing itself, the tangs on the plates, tha clutch basket and the primary chain as being far more prone to cause vibration.
Cheers,  

[Goldie]

Thanks for all your help guys.

I suppose the bottom line question is.

"When the A7 gearbox mainshaft was new, and a Norton spider was new, were they a snug fit"?

I don't mind forking out for a new shaft(if i i can sorce one) and a new spider, providing they fit together correctly.

I believe it is RGM Motors who supply Norton parts at reasonable prices, including clutch spiders.

[Goldie]

I have just had a mate up to measure the A7 shaft with a vernier, and the Norton mainshaft.

He said that he can see no signs of wear on the A7 splines, and there is a difference between them. 6thou on the OD and 20thou on the ID, so the BSA shaft is slightly smaller than the Norton.

What i have decided to do now is to source a A7 plunger clutch spider, and hopefully with some engineering work, fit it into the Norton shock absorber.

Maybe this is what they did to do the correct modification.

WANTED. BSA A7 plunger splined spider.

[Goldie]

Found the problem, by disconnecting the primary chain and starting the engine with a rope on the crankshaft and the noise is still there.
Split motor in half, and found that the inner drive side roller bearing case was turning in the crankcase.
3 new crankshaft bearings ordered, and i will fit them in using Loctite Bearing Fit. Checked flywheel alignment, big end and crankshaft for run out, and everything there is looking good.

[33d6]

Delighted to hear you have located the problem.
Isn't it amazing how nasty sounds travel around the bike and appear somewhere entirely different.
Congratulations on your problem solving.
Cheers,

[douglas]

Still dont know why that would cause a noise if the outer case bearing was undamaged?  Dugless

[Goldie]

Still dont know why that would cause a noise if the outer case bearing was undamaged?  Dugless

All i can do is but hope.

Now i am down the road this far, i am replacing all the bearings regardless. Like i said the crank,flywheels and big-end are in good condition.
Its a process of elimination as i work my way up.
The barrel has just been rebored and fitted with a Wiseco forged piston and the head overhauled by Gold Star specialist Phil Pearson

[db133]

Hi
sorry to butt in but........

I have been trying to find informatin on the mainshafts to make the conversion possible.





I am totally confused as to what fits what. For me its interesting and any information on the subject will be most appreciated. Kind regards.

PS Any information on the A group Gearboxes also appreciated.

[db133]

Thanks for your advice and info.
I have now found out that to use a Norton clutch on a BSA RRT2 gearbox, it must have had a BSA A7 plunger mainshaft fitted, which has a splined end the same size as a Norton mainshaft.
I have the measurements of the spline on a new Norton shaft taken from a Haynes manual, but unfortunatly do not have the measurements of the A7 plunger shaft, just to make sure that they are identical in size.

I would be very grateful if anyone could give me the OD diameter of the spline on a A7 plunger shaft, so i could then measure the shaft in the bike, before shelling out over £100 for a new shaft if needed

I have previously been informed :The only thing we had to do was change the mainshaft for a matchless one, it was common knowledge in the day. Maybe BSA internals were made by Burman as well, as it seems too much of a coincidence that they fitted.
you can fit a plunger mainshaft out of a Beeza A10 into a BSA swinging arm box to fit an AMC clutch which has the same spline. Burman B52 mainshafts also have a similar spline as the AMC box to fit the later clutch (which i have done) but it isn't a perfect fit as the spline is a little sloppy for my liking!
"BSA gearbox but mainshaft replaced with a matchless one ?"
I had a look on the web and can't find back-up for what I said, but I feel certain that it was a matchless shaft. maybe it was the A10 rigid shaft and I am wrong.

A little confusing for me.

Can any one clarify whats wot.

[rogerwilko]

BSA plunger mainshaft into swinging arm box will take an AMC clutch. Matchless B52 burman mainshaft will take the later AMC clutch which i have done. But it wasn't a tight fit. I wasn't completely happy with it so filled the splines with bearing loktite. So it seems the Plunger spline is slightly smaller like the B52, so i would be interested to see if plunger and burman splines are exactly the same.

[db133]

I have the mainshaft in the blue picture and that looks like the top one in the other picture.

I can measure it for you please let me know.

Do you know what layshaft I have ?