Type 85A engine breather

innellan House · #1 (**permalink**) 08-06-24, 07:24 AM

The type 85A engine breather is situated on the front unit of the inlet rocker box cover & connected by short hose to the air filter.
Can anyone please tell me how the bypass combustion gases get from the crankcase to the inlet rocker cover.
The path taken by the gases is not obvious on examining a sectional view of the engine. Thank you.

flyinghorse1 · #2 (**permalink**) 08-06-24, 07:42 AM

Via the vertical pushrod “wells “ on distributor side that go from camshaft tappets /followers to the rocker arms in cylinder head.( you can see this if you take tappet/ pushrod long cover off on distributor tower side.
I’ve an engine in bits atm so will try to send a picture.
There’s also oil return to sump from cylinder head at rear.
The breathing on exhaust side not that great if you use high revs.
Now you know what you are looking for you can just make out the vertical pushrods in your diagram.
Graham

innellan House · #3 (**permalink**) 10-06-24, 04:08 AM

thank you Graham.
Any idea if the movement of the gases is bidirectional - could the crankcase ingest atmospheric contaminants during piston upstroke? i.e. if the crankcase gases are routed directly into a downpipe (as when individual Vokes pancake filters are used) instead of being returned to the Bristol factory air manifold. Thanks.

flyinghorse1 · #4 (**permalink**) 10-06-24, 07:47 AM

I don’t see why not. On the Volkes air filter cars there’s an alloy breather on the side of block going to a catch tank.
I stand to be corrected but having thought about it:
As that’s all at atmospheric conditions the volumes would be much lower than any combustion blow by ( pistons/ rings ) and the pipe / catch tank arrangement would make it hard for any ingress of large particles.
Graham