Crankcase vent question

MikeG · Jun 27, 2012

My 71 Commando has the timed crank breather off the end of the cam, which I believe is the better of the versions till they went to venting thru the timing chest?? Is anything to be gained by adding a reed valve in the breather tube??
Thanks

1up3down · Jun 27, 2012

Is anything to be gained by adding a reed valve in the breather tube??

that depends, on whether your motor has persistent little oil leaks or not

if not, no

if yes, then yes putting in a one way valve in the breather line will help to lower the pressure in the crankcase,
and therefore possibly lessen or completely eliminate oil leaks from the crank into the primary and also around the cylinder base, etc

many here swear by its effectiveness, myself included

JimC · Jun 27, 2012

There is also the benefit of a power gain. Jim Comstock has some data on how much. So it's a twofer. Eliminate oil leaks that are endemic to a pressurized crankcase and gain a little power. All for about the price of a twelve pack of a good beer. How can you go wrong?

ML · Jun 27, 2012

No there is NO repeat NO advantage to add a in-line reed valve to the std cam driven breather hose.

Reason is the design operates as a timed aperature, on the compression stroke it opens 2 small ports and on the up stroke it closes them, thus the identical function to a reed valve. The deficiency is the flow path and volume is minimal that is why they moved to open crankcase breathers in 71 and again improved in 72 which do permit the negative pressure advantage of a reed valve.

Mick

DogT · Jun 28, 2012

That's what I think, since the breathing is already timed to exhaust the pressure, what would a valve do, especially with these tiny slots in the end of the cam.

You'd do better getting the sump breather or put a proper breather somewhere else.

Dave
69S

swooshdave · Jun 28, 2012

ML said:
No there is NO repeat NO advantage to add a in-line reed valve to the std cam driven breather hose.

Reason is the design operates as a timed aperature, on the compression stroke it opens 2 small ports and on the up stroke it closes them, thus the identical function to a reed valve. The deficiency is the flow path and volume is minimal that is why they moved to open crankcase breathers in 71 and again improved in 72 which do permit the negative pressure advantage of a reed valve.

Mick

I'd say that it's "identical" in that they both allow air to pass but otherwise the operation is quite a bit different. The holes in the timed breathers are so small I'd be surprised if they are efficient at all.

rpatton · Jun 28, 2012

swooshdave said:
I'd say that it's "identical" in that they both allow air to pass but otherwise the operation is quite a bit different. The holes in the timed breathers are so small I'd be surprised if they are efficient at all.

Check the last post in this thread. It's old. Most of these guys have probably died of old age by now but they were some heavy hitters back in the day.

http://www.eurospares.com/sucker.htm

Crankcase vent question

MikeG

Mikeg

1up3down

JimC

ML

DogT

swooshdave

rpatton

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