Hi. I’ve got a Dommie 99 (1960) primary chaincase that doesn’t have the two sealing disks fitted to the hole where the gearbox mainshaft enters the rear half of the chaincase. I’ve got two new new disks but I’m not sure if there should be a felt washer between the disks when they’re fitted to the chaincase. I’ve looked in the factory parts book but the disks aren’t listed so no help there!
I intend pop-riveting the disks together - any other ideas for fixing them?
I pop riveted mine on my Commando, works fine and once riveted together there is a slot for felt on the ID so that is fitted.
Hi, the discs should be fitted such that there is a gap between them at the centre and a felt ring (might be 012443?) should fit into this gap that will then slide over the mainshaft. Did mine over 20 years ago so a bit hazy as to whether there is an 'in' and an 'out' as to the discs orientation.
A spray of chain grease between discs and case will help seal against leaks.
Hope this helps,
I unriveted mine, on a 1957 99, ready for a total respray, there were no felt seals. After spraying I re-riveted them with copper rivets after fitting felt seals into both sides, “just for luck”. I can’t remember if I used the felt seal from the outer chain case inspection cover or the one that fits into the footrest tube through the cases but I would guess the former.
These chunks are known as Sealing Discs and are sold by both RGM and Norvil under Part Number 060769.
For your cash you just get a disc or possibly two if you remember to ask. What you do not get is the felt ring that sits between the two discs or any rivets to hold the dics together. These are lets rob you some more extras.
This part of the primary chaincase is the number 1 escape route for oil next to the big rubber sealing band. Especially if the crankshaft oil seal has seen better days and is allowing lots of crankcase vapour past into the primary chain area. This pressurises the cases and pushes both oil and vapour through the smallest of gaps.
A smart move, in this region, is to add another felt ring seal onto the gearbox mainshaft between the inner case and the clutch body. This will push the sealing discs flat against the inner and also make an extra seal on this shaft.