Having sorted out (I believe) by sticking exhaust valve (thanks for the inputs from folk on the other thread about that) I decided that perhaps it would be useful to check my gearing, and yes found that I had original WD M20 gearing with 19T engine sprocket and 18T gearbox. So the easiest option for aim for a more relaxed run is to swap for 19T for 20T engine sprocket. Modak Motorcycles here in Melbourne had just what I needed so I was all set.

Planning to do that job over two evenings after work, I head down to the carpark and make a start. Off with the footrest and the chaincase outer cover. Hmmmm, the engine shaft shock absorber had what looked like much or grease on the end, but quite dry. Looking inside the chaincase cover I could see that the engine shock absorber nut has been in contact with the cover and has been wearing it away, having just worn through

Now I should have heard that, but my hearing is not the best. This must have been like this since I did the gearbox work. What I don't know is why. I changed the engine shock absorber nut for a new one, as the other was showing signs of butchering with a chisel, maybe it is a little deeper? Maybe I missed a washer on the footrest and it's pulled the chaincase in a little. Either way some more repairs will be needed now, and some working out as to what has caused the two parts to come together.

I just wish I had ears that heard this kind of thing.

All comments and suggestions welcome

email (option): dickie.bobbie@hotmail.co.uk

This can happen of course if the cush drive nut comes loose. But by then you usually lose drive and a lot of rattling as the lobes pass over each other.

Ron

email (option): ronpier@talk21.com

Hi Ron

Yes, that was my first thought, but definitely not loose. I'll dig out the old it and check its depth. I now trying to remember if I found two gaskets behind the chaincase or anything else odd, but as that was Feb 2015 I have a very slim chance of remembering. The "why did make the tank off" forum photo is apt!

Cheers

Richard

email (option): Dickie.bobbie@hotmail.co.uk

I have found a few primaries where the inner was bowed backwards.
I put this down to DPO's smacking the retaining bolts with an impact driver and a 10 lb hammer.
Then silicon in place of the 1/4" thick gasket and the outer is running way too close to the sprocket nut and clutch dome.

email (option): bsansw1@tpg.com.au

Hi

Well the mystery is now solved, just the fixing part to attend to. I dug out the original shock absorber nut, removed the replacement (again) and compared. The new ones is a little over 19mm deep and the original is just over 16mm deep, so more than 3mm difference, enough to cause the problem I think.

Some photos below:


Left = New, Right = Original



Left = New, Right = Original


Still annoyed about the damage to the chaincase, but there's no undoing that. Trip to Modak tomorrow to hopefully source a correct shock absorber nut, failing that I'll need to find somewhere to machine down the new one to the right size. Need to get all of this done in time for the All British Rally the weekend after Easter, so had best crack on!

email (option): dickie.bobbie@hotmail.co.uk

This forum is such a good thing (as I suppose forums in general)!

The other day I for the first time tightened the screws to the primary cover. Later when I turned the engine over by the kickstart I heard a loud scratching noise...
Having just read this thread I understood right away where to look! I remembered that there was a build up with weld on the inside. Presumably from mending it after a fall or a tip-over.
I took a dremel and removed most of the buildup and I think that will do it. If not I will try a lathe away a millimeter or two on the nut (sorry for speaking metric).

/simon

There are two crankshaft nuts which look similar but are different dimensionally....

One for the 4 lobe shock absorber set up, one for the later 2 lobe set up...

The thicker nut is the one for the 2 lobe type...Ian

email (option): ian@wright52.plus.com

Good thing to know Ian (and I sometimes wonder how it is at all possible to know all the things that you know)!
Hopefully it will all be alright now after I addressed the somewhat clumsy welding that was there.

Note that I do not know if the bike was ever ridden with this fix done. I bought the bike in a state of initiated rebuild. The primary cases where for instance blasted. A reasonable theory would be that it was fixed and blasted at the same time, and that prior to that it was used with some temporary fix. The bike spent its life up until 1989 in Sri Lanka.

Anyhow, thanx for good info!

/simon