Forum

[PeteF]

There seems to be some misunderstanding here.
The pipe into the back of the timing chest is NOT a breather, neither does it suck air into the timing chest.
With the original setup the catch can is supposed to drain back into the timing chest via this pipe. The duckbill in this pipe is there to stop oil blowing out of the timing chest.
One of the reasons the system doesn't work very well is that, while oil will drain back, emulsion will not, so the catch can and this drain pipe with the duckbill gets clogged up. The emulsion then has nowhere to go but the air filter.
Also, there is always slight pressure in the timing chest, so oil can only drain back with the engine stopped.
If you remove the catch can the timing chest spigot needs to be sealed.
The whole system is a very crude way of attempting to stop any oil being lost onto the road which is demanded by emission regulations.
Further reading here

[wilf]

Thanks Pete, most informative. My current set up is as you have described.,with the exception of the duck bill, which I will order today from our hosts. Cheers, Wilf.

[Frank]

So if the timing side breather pipe has a NRV on it so that it can't let oil etc be blown out, and it doesn't suck, then what is the flow of air passing through the end of the pipe, and what replaces the air forced out by the descending piston when it's on the upstroke?

[PeteF]

Frank, OK, I grant you, the drain pipe might "suck" a little but that is not why it's there. Models made before the catch can was introduced had no such feature.
A negative pressure in the crankcase is generally regarded as good thing which this system will tend to destroy up to a point. The NRV on the engine breather pipe is specifically there to help maintain this negative pressure.
In reality, at speed, I imagine there will be very little negative pressure but the breather helps to eliminate positive pressure.

[Paulk]

Chaps,

If this helps? - the Bunn Breather system uses exaclty the pumping action of induction into the timing chest and and exhaust out of the oil tank breather outlet, using the displacement of the piston and non return valves. So substituting the Bunn nrv's with duckbills, would this not have a similar effect? If you read the Bunn info he (Bunn) says his valves work much better (but he would, wouldn't he (to quote MRD)) than duckbills. Admittedly the Bunn system uses different size valves (larger on the exhaust). I can't remenber if the original catch can is sealed from the atmosphere - I'm guessing not since there was a pipe to the air filter, so a duckbill in and out was a standard fit - untill it get blocked with mayo that is. I had the Bunn fitted to my Electra and cannot remenber any mayo.