I see that C15 sump plate sealing is a topic that has come up before... with the studs also under suspicion....
Has anyone found a solution that works? (Other than a drip tray!)
My B40 plate studs leaked for eons, around one corner/stud.
I'd tried wet sanding the sump plate on a glass plate, and checking all faces with the side of a steel ruler, with no success, but tried again last winter. This time it has worked, but I suspect the new slightly thicker softer gasket is the reason....prob just enough to deal with residual unevenness around the stud.
I believe just tightening the plate a bit too much can distort the alloy around the stud on the case..aiding a leak....with that lip then hard to file off with the stud in situ.
Hi,
Remove the studs and really clean/degrease the threads on the studs and in the case. Very slightly countersink the the stud hole - a twist with large drill by hand will probably be enough to just remove any raised material. Use some thread lock to secure and seal the threads. Do not over tighten the nuts. For that size of nut a spanner about 5" long is more than enough for leverage and use a nylock nut so over tightening is unnecessary to ensure that the nuts do not come loose.
Dave.
I find a hand countersink like this very useful for this kind of job.
(https://cdn.aws.toolstation.com/images/141020-UK/800/76122.jpg)
hoogerbooger - Can you by any chance remember the colour of the gasket material. Might help me in my search for the thick soft one....
Searched my email and it was on an 2025 order from Feked. Link to part here:
https://www.feked.com/bsa-sump-plate-gasket-c15-and-b40-models-circa-1959-65.html?srsltid=AfmBOoq5wUyhasU4XKw6BDpevZofPqIUI2nUgrLLBZ4EgCPS10BGrzwR
Looking at my sump plate I can still see that the gaskets are greeny/blue....so I'm fairly sure the picture on the Feked link is what I bought.
( my previous gaskets were ones I cut from gasket paper, which seemed to have little give)
For my A10 I used hylomar both sides of both gaskets so its gasket-plate-gasket-sump. I also had to helicoil the case (1/4 BSW) as two of the threads were stripped. You want to just squeeze up the gaskets, not clamp, as the soft gasket allows the steel plate to deform and then it leaks. In my experience these are always damp with oil, if its just a few drips I leave it alone.
My sump sealing has worked perfectly - so very happy.
But I have noticed that if the bike has not been used for a while, the wet sumping eventually results in a weep from the gearlever hole. This then runs down the cover - almost invisibly with clean oil - and form drips on the sump plate studs.
I've got a sump drain bolt fitted - so I think my new procedure will be to take it out as a matter of course. Or maybe I'll find some way to suck a couple of pints of oil out of the oil tank when I know I won't be using the bike for a while. (The wet sumping seems to stop when the oil tank 'head' is reduced to about 1/3 full.)
Do any of you park with the engine at TDC?
Yes. Engine has been at TDC for a while (with the barrel off) and the wet sumping has continued.
if it has been wet sumping to that extent, have you looked at the small ball valve that should prevent this?
I think it is just above the timing side main bearing
but how long are we talking about for it to ooze from the gear shaft - 2 weeks / 1 month ?? / overnight
Quote from: Tigerfeet on 20 Jul, 2026, 10:29 Yes. Engine has been at TDC for a while (with the barrel off) and the wet sumping has continued.
I would think it would be worth removing the pump and having a good look at it.
It takes about a month to get to the stage of leaking from the gear lever. The ball and spring were renewed and the pump is like new.
If it takes a month before it dribbles enough to ooze from the gear lever and that ball valve is new , then the simplest thing is to leave your drain plug out of the sump plate.
(I think you said you fitted one)
And of course ride it more to keep the sump emptied regularly