Does anyone know what torque to use when doing up the cam shaft nut C15?
The online robot suggests 35 ft lbs but I don't trust those things. I've not found it in Haynes or Ratio yet.
Hi,
35 lbs/ft should get it very tight but I think it has a lock/tab washer so a bit less would probably suffice.
Dave.
Thanks! Hugh Ferrier used a dollop of Thread lock on his. I don't have a lock tab washer, but I'll check out Fleabay.
I don't think it needs to be that tight, the tab washer or Loctite help. On a modern engine a circlip would do the job of the nut.
It looks very much like you do up the nut to remove any play and then rely on the clip (and/or loctite) to hold it on. I tightened the nut to around 30 ft lbs but it locked up the engine such that I couldn't kick it over.
I rewatched Hugh's video https://www.youtube.com/watch?v=Kw0FfvL5Lb8. He definitely torques the nut up tight but when I do the same it locks up the gearbox.
You may be suffering a lack of gearbox end float.
Ie , when you do the screws up that hold the inner co er to the crankcase, it tightens up the gearshift.
Undo the camshaft nut and secure the ring of screws , all the time checking happy rotation of the gearbox.
I suspect it'll lock up even without the camshaft nut
As soon as I undo the camshaft nut it slackens off and starts turning again.
As per previous threads, I changed the shims and added a gasket to improve the endfloat.
Which nut do you mean? There's no nut on the camshaft on a C15.
If its getting stiff when you tighten a nut then something isn't right. Its all got to spin freely when assembled at room temp.
As mentioned, you don't not have enough end float on the gearbox mainshaft.
If you grab the tapered end of the gearbox shaft , can you push pull it into the gearbox ?
If yes you have end float , if not you have no end float and need to investigate where it has gone.
My end float disappeared because I hadn't pushed the output bearing into the box far enough before reassembling.
This nut, which holds the timing gear and camshaft.
I can't get enough access to the gearbox mainshaft to wobble it now that I have reassembled it, but I was careful in changing the shim and adding the gasket to give enough end float. That was a whole seperate sage which I have already been through.
With the camshaft / timing gear, nut loose everything turns over fine. When I tighten up that nut it clamps the timing gear against the bearing and everything locks up.
As far as I can see the nut is there to remove the play, and Rupert Ratio suggest that you can run without that nut if the endfloat of the camshaft has been set up.
Also, since the shaft rotates anticlockwise it won't allow the nut to work loose.
SO howcome Hugh is torquing his nut up? One of us has to be wrong.
Thanks for posting that picture, I was looking at the wrong part! Since the later engines don't have a nut it can't be that critical. I see there is a tab washer 40-0117, does this fit into the wider slot in the thrust washer 40-106? An odd arrangement. I would take the cover off, put the cam in and get a measure of where the cam shoulder lies. It should be just proud of the bearing / bush by a few thou. If its binding it must be below. You can relive the bush slightly, it is new (I found new parts to often by out by a few thou). You could leave the nut just hand tight and rely on the tab washer and loctite but it would be nice to get the fit right. I doubt it needs more than a few lb-feet but what I don't like is the bush will expand more than the shaft so if its tight cold it will be worse hot.
I agree that it is an odd arrangement. Yes I bought that correct tab washer, so that will help, and the Loctite. I think this is something I might need to revisit. Thanks!
Looking at the parts book... if tightening that camshaft nut locks the camshaft (and everything else) then your problem is to do with the camshaft bearing's length. Or very possibly its 'setting'. With my C15F there was a procedure Rupert explained for finessing the camshaft endfloat. But I've no idea if that also applied to the other models.
Piccies I've found online show the camshaft having the shaft part terminating in a distinct shoulder and then the threaded end. So when correctly fitted you can tighten a nut up against the shoulder, whilst the shaft is free to spin in the bearing.
Did you fit a new camshaft bearing? From my recent experiences, they are not all ready for use (some weren't even made of the correct material). Fitting and then machining seems to be the BSA way. I'd suspect you need a fraction milling off the head of the top hat bearing. But I'm guessing!!! Hopefully someone who really knows will chip in!
I'd spent so long typing that up limeyrob got in before me...
What complicates things a little is the the side cover is a replacement from ebay, as the original cracked, so I have no knowledge of the condition, or setup, of the bearing.
Quote from: Tigerfeet on 29 Nov, 2025, 16:28 I'd spent so long typing that up limeyrob got in before me...
Lets call it a draw, we are clearly thinking the same way :)
Its also possible that there was some selective assembly at Small Heath and you've ended up with a short camshaft and a long bearing.
I'll start taking it apart again tomorrow, and start measuring bearings and camshafts. I still have the old bearings for comparison. It is really frustrating as I thought I was into the final straights of putting it all back together. It has been a long journey!
From memory on my C15 camshaft, the nut has a lock tab and a heavy washer under it.
When I did my nut up tightly, the big washer rotates just a whisker clear of the case face
I am sure you are right. That makes a lot more sense ;)
I'm getting somewhere now. It looks as though the side panel had new bearings fitted, but they should have had the flanges skimmed down after fitting, and they hadn't been. The cam shaft bearing stuck out around 0.5mm further than it should. This was easy to rectify by popping it out and replacing with one from an old side panel.
The gearbox bearing also needs fettling, and this explains why I just couldn't get the end float right, no matter what I did.
Sadly I don't have a lathe or a mill. Does anyone know if there is a tool, to go in a power drill to do this job, which I could buy?
Gbox bearing, just warm up the cases and ensure it is tapped fully home and of course the high gear into the bearing.
As you're in that far ,(dismantling clutch and gearbox internals) just use the box main shaft on its own , place into the box and offer the inner cover , only need a couple of screws nipped to establish what end float you have or don't have , when you grab the tapered end that sticks into the clutch. No need for the whole gear cluster.
Then you can work out any shims etc
Yes, I've done all of that before. I guess I am asking if there is a neat way to skim a little metal off of the gearbox bearing flange without having to mill it or drift it out and stick it in a lathe. (neither of which I have).
I thought to file it down, but it may not be sufficiently precise.
How much has to come off? A fine file will do the job, draw file at (say) 60 deg steps and check every now and then to see if there are high spots. You could try a stone wheel in a drill, but from bitter experience slow and by hand has a lot less chance of going pear-shaped.
I believe the BSA way is that you insert the bearings, and then machine them to get the required clearances. I'd guess that if you were knocking them in and out repeatedly you would lose the interference fit, and probably not seat them identically in any case.
I would have thought you were looking for a couple of thou of running clearance. This may be a level of precision that is very hard / impossible to achieve with a file. I don't know - as I've never tried it. I would suggest having a play with a scrap top hat bearing in your old cracked case, to see what works - just to avoid wrecking a good one!
what is troubling me is the fact that you have had to go to this trouble with bushes etc to achieve the end clearance/float.
I cannot help but feel that the gearbox bearing and the sleeve gear pressed into it are not home fully - this would cause all manner of grief in reassembly.
there are 3 thicknesses of mainshaft shims for the mainshaft in between the high gear and the rest of the gears on the mainshaft.
Quote from: Barnsey on 29 Nov, 2025, 15:06 I can't get enough access to the gearbox mainshaft to wobble it now that I have reassembled it, but I was careful in changing the shim and adding the gasket to give enough end float. That was a whole seperate sage which I have already been through.
With the camshaft / timing gear, nut loose everything turns over fine. When I tighten up that nut it clamps the timing gear against the bearing and everything locks up.
As far as I can see the nut is there to remove the play, and Rupert Ratio suggest that you can run without that nut if the endfloat of the camshaft has been set up.
Also, since the shaft rotates anticlockwise it won't allow the nut to work loose.
SO howcome Hugh is torquing his nut up? One of us has to be wrong.
No specific torque figure needed, just tight with a normal length spanner for that nut, then the tab washer will stop it undoing.
If the Camshaft locks up when the nut is tightened it is likely because the cam bush is protruding too far through the casing and the washer under the nut is pinching against it.
The outer end of the cam bush needs to be flush with the machined surface of the inner cover around it.
The inner flange of the cam bush may also need reducing in thickness to ensure the shoulder of the cam outer journal, behind the thread, stands proud of the outer end of the cam bush and inner cover by a few thou. If it doesn't that's another cause of the cam locking up when the nut is tightened.
I managed to get the end float on the gearbox bearing down to around 0.09 to 0.18mm. Not easy to measure it accurately with the butt end of my digital vernier calipers. I trust that is Okay?
Next I'll check the new camshaft bearing for clearance.
This is what I got from the Google AI:
The recommended gearbox end float (end play) for the BSA C15 mainshaft and layshaft is approximately 0.003" to 0.005" (3 to 5 thou).
Some sources suggest a slightly higher figure might be acceptable for the layshaft in some cases, with one mention of around 0.030", but the general consensus for proper operation and to avoid excessive wear is in the tight 0.003"–0.005" range.
SO, my measurement of 0.09 to 0.18 mm is around 3.5 to 7 thou. Either, nicely in range or just out.
I am pondering whether it would be worth, fully stripping down the gearbox again, and fitting a slightly thicker shim. it currently has the thinnest I could find. But it may not be worth the effort.
Thoughts? Maybe it is time to invest in a DTI.....
I wouldn't rely on Google AI to tell me the day of the week. If it doesn't know, it makes it up... Have you got Rupert's book?
Rupert talks about 'just perceptible endfloat'.
I'm sure I wouldn't go chasing 2thou that might not even be there. You've got a tiny bit of end float, so it won't nip up when hot. Move on to your camshaft issue would be my two penn'orth.