A10 engine breathing

[iansoady]

I've been struggling to work out how my 1961 Golden Flash engine breathes excess crankcase pressure. I can see the shrouded hole in the timing chest but where does that lead to?

I've replaced all the gaskets that were leaking copiously but would like to make sure that crankcase pressure is being properly got rid of before starting it up.

PS - if I have to split the crankcases I don't think I'll bother.......

[bsa-bill]

not sure I follow your shrouded hole description Ian, do you mean the hole beneath the Magneto at the rear of the timing case inner cover, if so this is the blanked off drilling that goes up towards the camshaft then horizontally across the rear of the engine and exits on the rear of the drive side of the crankcase, reach a finger in over the primary case just down and in from the front maggie pick-up and you should feel the hole.
Pressure is released from the crankcase via the top hat breather that sits on top of the camshaft pinion with a cork washer between it and the inner timing case cover, every revolution of the crank ( twice every revolution of the camshaft ) a hole in the top hat breather will line up with the drilling and allow pressure to exit via the drilling.
I've just put the timing cover back on my bike , otherwise I could have posted a pic that would have explained it better.

[iansoady]

Yes that's the one I meant. I thought that it was part of the breather system - on rereading of your post I think it is. I'll have a look for the hole you mention. Having just come from a Velo which breathed via slots in the mainshaft into the primary drive case I'm not used to this level of sophistication...

I've just started it up (courtesy of a recon ATD from Roy Price - excellent quick service) and it now seems to run very well and so far no sign of oil gushing out.

[madsens]

Bsa-Bill (sorry Iansoady, not trying to pinch your tread)

I get a fair amount of air/oil puffing out of this hole you mention behind the magneto - enough to clearly mark where my a10 1962 has been standing - and also enough to spread out under the engine - is that normal, or am I having some kind of problem with leaking pistonrings or something else?

regards
Joergen

[bsa-bill]

 sounds like the infamous, dreaded, end of the world - wet sumping syndrome, I used the word syndrome instead of problem you will note.
If your bike stands for a good while between starts oil can seep past the pump into the sump, normally it's not enough to be noticeable as once the engine runs the return side of the pump ( has a larger capacity than the feed side ) will quickly clear the excess and normal service is resumed.
If the bike stands still long enough there could be more oil in the sump than the return side can get rid of and oil will be forced out of the sump with air ( via the engine breather circuit ), so the floor marking thing.
If you do a search here for wet sumping you will find many and varied opinions about it and cures and fixes, all valid depending on your preference and circumstance ( avoiding the wrangle of tap/no tap opinions folks).
It's not a problem for most I reckon, probably accounts for the "smokes a bit to start with then clears" remark oft times heard.
Other causes of air being blown out there, - blow by - due to worn rings, bore