O ring primary chain

Seen it done on racing bikes with typically short runs before re-greasing but they are wider than a standard chain so you need clearance. If you don't have the clearance then back to standard and sort out the leaks. An X ring chain in the same size will be marginally narrower with DID being the narrowest.

Hi Terry,

The speed of the primary chain gives o ring chains a very, very hard time. When I enquired a few years ago they were 'not recommended' by the experts due to heat build up.

As John said,  sort out the oil leak - the 'tin' cases can be made oil tight.

Regards, George 

A drawback using O-ring chains is that friction makes them less efficient than an open chain. X-ring chains slightly better but still not as good as an open chain. In classic racing where we have less power than modern bikes we usually have open chains to get as much power to the rear wheel as possible. Top enduro and motocross riders often use open chains where even a small increase in transmitted power counts. Less skilled enduro and motocross riders prefers sealed chains, making maintenance.easier and cheaper.

Hi Terry,  While you are in there  check carefully the clutch center where it mates with the gearbox shaft  ,a known weak point , sometimes allowing the clutch spider face  to drag heavilly on the sleeve gear end. Also a good time to check the rear drive sprockets are in good alignment .

One thing not mentioned is the lubrication of the bearings.

On a race machine this is done periodically.

As said, best thing is to go back to standard chain while checking the sprockets for wear and repair any leaks to the chain case, mostly caused by being put on too tight, causing distortion.

Then find some SAE 20  BUT never use anything even slightly synthetic.    

I use ATF with no problems

dan 

I have a quite a bit of ATF spare, as I used to use it in my Mk3 Commando until I read in RH that it is no good for the hydraulic chain tension.

I'm down to my last ltr of SAE 20, there after I could use SAE 30 or even 20/50 the original spec for my commando.

I'll use the ATF as a last resort but, that's about all.

Main issue with my 650 is that every couple of hundred miles the primary chain gets tight, slack I could better understand it. Anyway, perhaps a topic for 2022.

Hi Neil, I have used ATF no problem ., and it has helped to pinpoint where leaks orriginate . Primary tightens when a sudden shock  pulls the box back. Even if you follow the advised method of overtightening  then final forward setting. If its a continued problem then you need to be suspicious of the  top mounting box coach type bolt ,which can seize in the alloy tunnel or dig itself a hole in the engine/box plate behind the primary inner case.This makes a joke of any attempt to adjust the primary.  Usually a box out job to sort out with grease and a bit of file work.

There should be a spacer tube, numbered H40 in the parts list illustration, part number 15641. That ought to prevent the engine plates being squeezed together (unless it is too short).

The spacer tube is ocasionally missing as some  owners  can't see the point !, thats why you can see buckled engine plates sometimes and 4 or  5  threads showing at the footrest .The last SS I worked on was like that with footrests that would collapse under pressure. I had a job convincing the owner that it was worth a stripdown to put right.

Looks like you are well on the way to sorting your primary case issues out, Terry.

The spacer tube is very important. You should now only have 2 or 3 threads showing when the L/H footrest is tight to perfection.

Robert is right in that the red ATF will help detect any leaks. These tin cases can be made oil tight, so far I have made three of them so. When fitting, give the case a light tap all around with a hide mallet to ensure it is properly seated.

And Robert, I have a rattle with my 650 and when I take the engine out to look at the cam followers and below (Seen to the top end) I will change the gearbox while at it. But I think you hit the nail on the head and with all that stretching I think a new standard Renolds primary chain will be in order. (Engine been rattling for over 2,000 miles now and no worse.  Hmmmmm)

I put up with a rattle on the 99  .  Could have been tight fit  of the  99 pins in the 650 pistons  and the short skirts   or loose rocker spindles , Only things I have changed  are  fully synth oil and Rgm  spindle kit . .Quiet enough now. Who knows !

see page 16 of Nov. Roadholder magazine, and archive on NOC site about distorted chaincase.

My Dommi 99 is in fact a fairly original looking to the untrained eye a bitser that I assembled more than 55 years ago. It started out as an early 88 with dynamo electrics and the corresponding tin chain case with the small bulge over the drive sprocket. The 'rebuild' ended up with a 99 engine with an alternator and it's corisponding larger bulge chain case. 

Getting to the point. I've always had the dreaded primary chain case leak problem. I just read an article over 20 years old by the great John Hudson showing the chain case fitting and the well known consequences of overtightening the retaining nut. Now when I fit my outer cover I have to fully tighten the nut in order to expose the footrest surrations and ensure the footrest does not slip. It has taken all these years for me to think that maybe the surrated  stud is of the old style chain case and that of the alternator chain case maybe different lengths, logically the older smaller chain case being shallower than the latter and this being the case, have I fitted the wrong stud? Any answers please.