E: Engine PCV Valve

[Chris Launders]

My JAPs have a timed breather almost identical in action to the Vincent one, they also have NO crank seal arrangement, literally there is a single open ball or roller bearing and the mainshaft comes out through the casing.
Interesting they don't leak either, the valve is timed to open 90 degrees before BDC of the crankpin whether it's a single, 50 degree or 60 degree twin, total loss or recirculating.
You can tell if you've got it wrong, you get oil coming out everywhere !!

I have checked the duration of the opening, 90 degrees, so it closes at BDC and is a 3/4" long slot

 

[vibrac]

I dont see the point of all the timing mularkey
you have a pcv one way valve the piston goes down the air is pushed out of the engine
the piston goes up no more air comes under the piston since no or very little compressed air or combustion comes out of the valve guides or down the side of the piston
the piston goes down again little air goes out of the valve and by the time you put it in gear most of the air movement has ceased and any oil it carries outside is negligible.
a negative pressure in the crankcase is not a great advantage from performance point of view power saved on the down is probably matched by suck going up. but a PCV valve means all that big bore breather pipes , catch tanks, timed breathers etc have little part to play
But to repeat an engine in poor condition will extrude oil from a breather whatever the type

 

[Cyborg]

I dont see the point of all the timing mularkey
you have a pcv one way valve the piston goes down the air is pushed out of the engine
the piston goes up no more air comes under the piston since no or very little compressed air or combustion comes out of the valve guides or down the side of the piston
the piston goes down again little air goes out of the valve and by the time you put it in gear most of the air movement has ceased and any oil it carries outside is negligible.
a negative pressure in the crankcase is not a great advantage from performance point of view power saved on the down is probably matched by suck going up. but a PCV valve means all that big bore breather pipes , catch tanks, timed breathers etc have little part to play
But to repeat an engine in poor condition will extrude oil from a breather whatever the type

Adding a PCV valve to Vincent ridden on the street isn’t likely to result in any significant power gain and a PCV valve will do ok for the RPM’s it will see. My guess would be that a valve of some sort would be better than no valve at all.…. especially in an engine with some blow by. Again a guess, but the valve would likely reduce oil dilution. On a race engine ridden at higher RPM’s a reed valve will do a better job. All those Japanese engineers can’t be wrong. Incremental gains add up. It’s not just the pressure… in some cases you can run lower tension rings, so less friction. As for using vacuum pumps, engine builders are actually getting very noteworthy gains because with the pump, they are getting much better ring control.
It’s obvious from the plumbing in the video that these guys have studied the subject. I suspect the results were good because they ended up using a pump.