[Thomas]

Thank you, Rock, that makes entire sense.

My surfaces are in good condition and I can try a sealant. I have Weicon Silicon Black Seal (generally fine), Hylomar (successfully used for my crankcase) and CurilK2 (used for my BSA primary case). From my subjective feeling I would try Hylomar and then see the outcome.

The end-float as a check seems to be difficult from my point of view. I mean, how can I check it when the timing case is closed? I also think that there is no critical end-float at the camshafts because the inlet shaft runs the timing chain (no end-float necessary) and the outer is connected to the valve lifter (also no end-float). Both bushes are designed as dynamic seals. Theoretically, only the crankshaft on the timing side could be critical. But is that really a real problem considering a 10 to 20 thou gasket?

But paper gaskets do have one advantage: they do not stick. 

Cheers, Thomas

[Rick Parkington]

Hi Thomas, I think there were no gaskets in the timing case or chaincase from new either and in my experience it is rare to see paper gaskets ('joint washers' as they were usually called) on any 1920s engines other than the base gasket as John points out.
I guess when the engines were new, with freshly machined, smooth, dead flat joint faces all that was required was sealant - 'seccotine' (a kind of glue) or a shellac varnish was sometimes mentioned. Paper gaskets were probably fitted by owners trying to resolve leaks once the bikes were older and the cases scored, chisel damaged and warped by careless owners. Nowadays silicone RTV gasket sealer offers the best of both worlds. 
One clue to whether a gasket was fitted originally is to check end-float on a shaft, eg the camshafts - if there is none with the timing case bolted up bare, you know you need a thin gasket but similarly fitting a gasket where none was originally fitted will lead to excess end-float which may be a problem.
Cheers Rick 

[Thomas]

That could answer why I have a very small amount of oil at my cylinder base. I will make a gasket and check it out. But what about the timing box and the primary case? Should there be gaskets at all?
Cheers, Thomas

[singleminded]

for my 1932 9A the only gasket listed is for the cylinder base/crancase joint.  John.

[Thomas]

Remarkable! So, no gasket at the head, nor at the timing case and the rocker box (there was one, too). I should update my overhaul manual... So, were there gaskets at all at, e.g., the lower timing box and the primary case?

[phutton]

No Thomas, there isn't any reference to a gasket in the rocket box in any of the parts lists.

P.

[Thomas]

Aha, this is new to me! I had a gasket in it. Since I have the housing open right now, I'll try it without a gasket. What about the rocker box cover? Did it have a gasket originally?

[phutton]

Vic is right - there is no gasket mentioned in the parts lists for any model or year.

P.

[Thomas]

I also think it should be unnecessary as there is no oil in the chain case or at least a minimal amount from leakage from the pump/sprocket spindles.

Hm, I'm not sure about that, Vic. If that would be true the chain would need to run dry. There is always some oil in it. Atached is a pic from my chain case interior before cleaning.

Best, Thomas

[VicYouel]

I do not believe that a gasket was fitted by the factory and I don't think it is mentioned in the parts list.....although I have not done a thorough check.

I also think it should be unnecessary as there is no oil in the chain case or at least a minimal amount from leakage from the pump/sprocket spindles.
Vic

[Holbay]

Thanks for Rick for your input.

[Rick Parkington]

Hey up,
Just to say that personally I'd avoid using thick paper as it's usually the cause of distortion in the first place. If you imagine tightening the two cases together metal to metal, they cannot distort because the area around the screws touches at the same time as the area between. But put in a squashy gasket and the area around the screws will compress more than the bit between, potentially distorting the case. You see this most commonly on old Amal monobloc flat bowl covers; without a gasket they touch at the screw holes but nowhere else!
The same (but different) applies with the earlier Sunbeam case with two centre bolts. Again provided the bosses for the bolts are dead level with the joint face no harm can be done metal to metal - but add a paper gasket and you'd need to very carefully space up the bosses to prevent the bolts drawing the centre of the case in. Even putting gasket paper washers onto the bosses doesn't really help because again the bolts will exert more 'crush' on them than at the gasket face which will tend to flare outward - this is what happens with centre bolt Norton tin primary chain cases.
If your case isn't warped I'd use manila envelope for the gasket - as advised below, with sealant if you choose. If the case is distorted I'd suggest silicon RTV gasket as it will reman thick where it needs to and squeeze out elsewhere without loading the joint and adding to the distortion.
Hope this helps
Cheers Rick

[Thomas]

OK, if the surfaces are somewhat worn you additionally can apply a thin sealant layer like Wellseal or so. If the surfaces are badly worn or damaged (what would be surprising) you might need to grind them on a flat surface (e.g., glas).

Cheers, Thomas

[Holbay]

Hi thanks. Now looking at it and I'd say the gasget can't be to thick as the oil pump peg on the casing cover has to engage with the drive from the engine. But with the age of the machines the two facings will not be flat anymore so a little increase in gasget thickness will be advisable me thinks. Any other thoughts most welcome

[Thomas]

Hi!

There is no specific reason for the gasket thickness and "thin" is a matter of definition, I believe. Simply take the old one as a draft. If the cover and case surfaces are undisturbed you can use the thinnest gasket available. As far as I remember I applied an 0.5mm gasket. Even an 0.1mm would do the job, I suppose.

Cheers, Thomas

[Holbay]

Hi. Need to make a new magneto chain case cover gasget. The old one is so so thin and would difficult to make. Can I use thicker material to make a new one. Or is their a reason the gasget is so thin. Thanks