Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A65 Clutch Rebuild

Hi all,

I am posting this thread about some problems I had while rebuilding the primary drive and clutch on my 1966 A65 Lightning.

I am hoping that the information may be of help to anyone who encounters the same problem I had.

My gearbox has been rebuilt using about 80% brand new components, including the main shaft, and all end floats and other tolerances are well within factory specification.

My primary drive consists of brand new triplex chain, clutch sleeve, thrust washer, 20 off roller bearings Dunstall alloy chainwheel, complete clutch centre / cush drive assembly and main shaft nut.

After spending a bit of time with a little jig I made, to temporarily hold the clutch drum tightly on to the clutch sleeve and thrust washer, I made the primary chain alignment correct. This needed a shim in between the crankshaft distance piece and the front sprocket.

Once the chain alignment was sorted I fitted the engine sprocket, chain and chain wheel along with the thrust washer and 20 roller bearings. I then fitted the clutch centre, washer and main shaft nut. When I tightened up the nut the clutch centre fouled against the clutch chain wheel to such an extent that it locked the whole clutch assembly up and started to turn the engine over, even though there were no clutch plates fitted. (see attached sketch)

I had to take the whole lot off and get it all on a surface plate to check all the relevant dimensions with a combination of micrometers and slip gauges.

I ended up having to take 0.040" off the back of the clutch sleeve, on the surface grinder at work, in order to give me enough relief for it to clear the inside of the chain wheel. Once this was done and I tightened up the main shaft nut I could get an 0.008" feeler gauge all around the gap in between the clutch centre and the chainwheel. The centre hub still felt a little tight to turn, and referring back to my previous measurements, I took 0.002" off the thrust washer and that did the trick. The whole lot is now fully assembled with correct clearances and feels nice and snug and the clutch centre turns freely by hand without interfering with the chain wheel..

All my parts were sourced from reputable suppliers such as SRM and BBB but it just goes to show that not everything fits out of the box. The only non standard part is the Dunstall alloy chain wheel and I don't know if this is what caused the problem? It compares very well with the dimensions of the original, so I doubt it. The complete clutch centre was purchased from SRM, along with the clutch sleeve, woodruff key, thrust washer, roller bearings, main shaft nut and Norman Hyde clutch plate kit. The clutch centre was different, dimensionally, to the original part and I think that this is where the problem originated. I rang SRM and spoke to Geoff about this and he told me that the only problem they had encountered was sometimes the thrust washers needed a little taking off them.

The 40 thou' I had to take off the back of the clutch centre was a little more severe than this and I have informed SRM with photographic evidence of the steps that I had to take to resolve the problem.

I don't want to have a go at suppliers because over many years I have used many of them and I have had good and bad experiences with most of them. On the whole it's been good and particularly with SRM I have always been very happy, in the main, with their parts and service.The only time I had a major problem with them was a long time ago when Steve Mcfarlane was still there. Although it caused me a bit of grief at the time, he sorted it out for me eventually.

Cheers,

Kev E

I had a similar problem of interference with a Triumph clutch that I worked out with help from this forum.

https://www.britbike.com/forums/ubbthreads.php/topics/775761/1

Long story short, not having a lathe or any fancy tools like that, I used my drill press and a flat stone to grind down an area on my
chain wheel basket where it contacted the center hub. Mine was probably an EMGO.

Hi Nick,

Thanks for the link, I never read that before and it's interesting to see that other people have experienced the same problem.

Glad you got yours sorted with a good improvised method.

I'm lucky enough to have a very well equipped machine shop where I work and as such it makes work like this very easy for me to sort. It must be really frustrating for a lot of people who only have access to 'normal' tools.

Was your EMGO clutch centre a complete assembled unit (cush drive rubbers etc) and where did you buy it from?

Cheers,

Kev E

Yeah, no my problem was with the chain wheel basket. The part with the sprocket that the clutch plates fit inside.
I was getting interference in the same place as you I believe.
But I did need a new hub as I recall.
If I can make it work I'm sure you can with the machine shop!
Good luck!

Being a cynical old sod, i find this sort of thing pretty typical with
many new parts supplied now.
Good you spent the time sorting out the problem.

I used to have one of those Dural alloy baskets on mine, it wasn’t branded as Dunstall back then but I got it from BBB, it was actually very good and lasted well. However I used an original clutch centre and found the opposite problems. There was quite a lot of wobble with no plates in. The clutch Cush drive was pretty well worn in every way possible. From the spider to the back plate. However the more I flatted and removed the wear from the back plate of the clutch drive the more tighter that clearance got and wobble got much less. I can’t remember how much less, by the time I got the clutch working something like decent I had already bought the Bob Newby and still glad I did. It ended up on a friends bike and has been fine since.

I’d be interested to take one of those new centres apart and compare it against the A and B series clutch centres. The B series are narrower and i wonder if who ever is making them, is making them to the correct specification.

Hi Allan,

When I compared the overall 'thickness' of the complete clutch centre that I bought from SRM it was approximately 1mm larger than the original that came off the bike. I'm not sure what the clearance should be between the back of the clutch centre and the chain wheel drum but I would imagine it's not that critical as the friction plate goes in first and therefore the plain plate would have plenty to bear on, as long as the gap is a bit less than the thickness of the friction plate.

I had to take 40 thou off the back of the clutch centre, which is about 1mm, so that seems to tie in with the difference I noted. I definitely think that the clutch centre was the cause of the problem. I still don't know the exact clearance is from the back of the clutch centre to the chainwheel, as it's not an easy place to take an accurate measurement. I know that I could get an 8 thou feeler blade all around it but because of the lack of space in there and the fact that the inside of the clutch drum in that area is not entirely flat, that was about the best I could do. The important thing is that there is enough clearance.

Once I had it clear of the chainwheel, I bolted the loose clutch sleeve, thrust washer, rollers, chainwheel and clutch centre together with a long bolt and some thick washers. I then managed to accurately measure the gap between the chainwheel bearing outer race and the inner shoulder at the back of the clutch centre with some slip gauges. I compared this with the other measurements of the sleeve, thrust washer & chainwheel and this confirmed that the gap was a little tight. I only had to take a couple of thou off the thrust washer to resolve this and now it's all assembled it feels absolutely spot on. It spins freely and there is hardly any 'wobble' at all on the chainwheel.

Have to say I like the alloy chain wheel, it just looks & feels nice and saving all that weight spinning around in there can't be a bad thing?

Cheers, Kev E

See you soon.

Hi Kev,

Glad to hear you have sorted the clutch problem out.

With regards to your new alloy chain wheel, I fitted one to my 66 Spitfire 11 years ago when I completely rebuilt it. It was from a reputable company. Did all the necessary chain alignments etc, new 7 plate upgrade etc. After 3500 miles I got a slight noise from the primary area which increased as the mileage increased. When I drained the oil it was a strange metallic colour. Stripped the primary down and found that the alloy chain wheel around the inner teeth had worn at the side by at least 10 thou. All the worn away alloy had contaminated the oil so had now buggered the new chain and buggered the thrust washer
along with the rollers. Spoke to the late Ian Bell who used to race these lovely engines in his sidecar (long before he raced Yamaha engine sidecars) and he told me that this was a well known fault with alloy chain wheels and the racers used to replace them every year. He told me to go and buy a nice new original steel one and put that in. I followed his advice and so far after another 10000 miles I have had no problems what so ever. I hope the new alloy chain wheels are built and engineered better than the one I had and the ones Ian told me about, but I would recommend you check the colour of the oil on a regular basis, it works out cheaper that way.

Hope I haven't put you off having one installed as I'm sure they are far better these days. Mine was anodised a grey colour and it did look good..

All the best

Keith.

.

Hi Keith,

Thanks for the information regarding the alloy chain wheel.

Hopefully my alloy chain wheel will be ok but I will certainly bear in mind what you have said and keep a close eye on things.

I won't be doing a great deal of mileage on the bike. I would imagine it will be less than 4000 miles a year and quite possibly much less than that.

I'm strictly a fair weather rider now and personally I get as much enjoyment out of rebuilding and renovating, as I do riding these days.

Take care.

Cheers, Kev E