Engine breather mod?

[Ozmadman]

I was speaking with another lightweight owner on the telephone the other day and in the conversation he mentioned that a mod was often done to help the engine breathing on these models. Basically, a hole is drilled into the oil filler cap on the front of the engine and a pipe fitted and run down the frame under the tank?? I have never seen this of heard of it done before, has anyone else and for what advantage? there is a breather already on the timing side crank that should relive crankcase pressure as the crank revolves. thanks

Paul

[Les Howard]

This is another one of those nonsense ideas. The built-in oil tank is separate to the engine and does not see any crankcase pressures, same as a remote oil tank doesn't. The only gas pressure that can occur is when the scavenge pump has emptied the sump (a short lived event) the pump might then pump a very small amount of air into the tank, but this pressure build up is self limiting and stops when equilibrium is reached. Who would want an ugly pipe sticking out of that attractive oil tank cap anyway?....Les

[Ozmadman]

Yes, that's what I thought, I wasn't going to do it anyway but was just curious. I do have though in my oil tank, if you look very carefully with a strong light, up high and above and slightly to the rear of the return hole a very small hole, is this some kind of breather? this has been mentioned before I think and not all lightweights have them as far as I know. thanks

Paul

[Les Howard]

It's something that I have never noticed but maybe there is a hole, possibly an oil drain from the push rod tunnel and if so then the oil tank might "see" some small amount of pressure created by valve guide leakage down the push rod tunnel or slight gas leaks through the timing side main bearing and up the push rod tunnel. Since these routes are pretty small and tortuous with quite a bit of air resistance, you won't be seeing the real heavy pulsating crankcase pressure at the oil tank if the hole does link up. .....What I would also add is that any breather vent-hole or pipe needs some form of valve to minimise pumping losses and to also create a partial vacuum which is better than just releasing piston blow-by at slightly above atmospheric pressure. Will be interested to see what others say as regards the hole you mention...Les

[Ozmadman]

Thanks again Les, useful info..

Paul

[Les Howard]

Just an incidental extra ...but no value here for your question....(now back on view)...I found this really excellent exploded engine view....click to enlarge even further....makes a nice print:
http://1.bp.blogspot.com/-ShGWB6WKtpc/T ... engine.jpg

Les

[Ozmadman]

Just an incidental extra ...but no value here for your question....(now back on view)...I found this really excellent exploded engine view....click to enlarge even further....makes a nice print:
http://1.bp.blogspot.com/-ShGWB6WKtpc/T ... engine.jpg

Les

Thanks, it is nice but no timing side images??

Paul