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.