PVC valve installation

I'm considering installing a PVC valve and have been reading up on the resulting positive effects one has on this motor. It's said that the Commando motor has a couple pounds of positive pressure inside the crankcase, which is responsible for a large portion of oil leaks. Dumb question, but could anyone explain how this relates to oil pressure, and is oil pressure affected by the ambient pressure inside the case

It isn't related to oil pressure, just that high pressure in the cases finds ways to push oil out in places you don't need it leaking out. Tach seals, Pushrod tunnels, mainseals, etc, etc. High pressure in the cases would also push air out of the same spots, it just happens to carry oil with it.

Russ

PS - I have never seen it discussed but I would think it could be argued that by providing negative pressure in the cases through the use of a reed valve that oil flow to the sump would be improved.

Its decades old upgrade that lowers inside pressure below ambiant so air tends to suck in rather than blow oil out. I've had success as so many others with just cheap MotorMIght Brake valve, as only need to lower PSI a few points to work but you can get away with more bore/ring, valve guide wear if spending on the extra efficient reed valves. Yes lower case pressure helps oil pressure flow through better, if that was even an issue to worry on crank sling pressurized Norton crank. Norton dropped oil gauge option in 1st season issued on Commando as PSI showed 0 even at speed, but not really an issue, so Norton cut the freaked out calls the easy way. Norton real oilling issue is to keep over 1800 rpm for cam/lifter oil surfing.

Robb2014 said:

Dumb question, but could anyone explain how this relates to oil pressure, and is oil pressure affected by the ambient pressure inside the case

Click to expand...

There was a thread years ago on either the NOC or BritIron lists. Someone mentioned that they noticed a significant drop in their oilpressure readings after they installed a PCV valve. It was determined by the cognoscenti that it was due to the lowered crankcase pressure. It would have been nice to have the before and after oilpressure readings and the before and after crankcase pressures.

I've had success as so many others with just cheap MotorMIght Brake valve...[/quote]

+1 fellow Nortoneer Steveorino! 8000+ miles with my cheapy MotorMighty....not a single drop under the bike!!

Lower oil pressure by just crank case evacuation implies lower oil flow resistance so likely a good thing worth a bit more power at the tire or fuel economy. Never heard a report of too little pres sue inside hurting our engines, just sucking the oil out with the air. OIl seals can get sucked inside out so very effective suckers need those reversed. Don't ignore effective air grit filtering as source of ring gap and sealing wear for more blow by to handle.

Yes, the little Motormite works. The issue is that they do not last as long or function as efficiently as the better reed type unit available. Yet, at 6 bucks a pop, you can change it every spring and be fine forever.

Robb2014 said:

Dumb question, but could anyone explain how this relates to oil pressure, and is oil pressure affected by the ambient pressure inside the case

Click to expand...

I found the reference to crankcase pressure/oilpressure. They are a collection of posts from the Thumper and BritIron lists put together by Michael Moore at Eurospares.

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

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From: MoPerfServ@aol.com
Date: Sat, 20 Apr 1996 09:45:36 -0400

At the AETC (SuperFlow) conference in '95 one of the attendees was asking about oil pressure loss in heavily evacuated crankcases.
They had noticed a 10 PSI loss, according to there gage.
Neal Williamson, (SuperFlow President) offered, in reply, that the oiling system relief valve was referenced to the crankcase pressure, and the pressure gage might be referenced to atmosphere. Everyone in the audience, who was thinking about the problem, went; DUHHH!!!!
The point is, that, on this particular drag car they were running 10 PSI crankcase vacuum! This was generated by the scavenge pumps.
I did a lot of breather testing on Onan engines, (42ci boxer, flathead) and when a reed valve breather was used, you could see the crankcase pulses shift toward the negative.
The average was negative but there were still positive pulses.
The benefit to all of this was for oil control, (inconclusive) and leakage control.
Any power gains were too small to be measured.
Keep in mind that these generator engines are low comp., 3600 RPM things and not Grumpy Jenkins 9000 RPM Pro-Stockers.
About the negative pressure not letting the piston rise; remember it helps the piston fall, net ZERO.
Allowing the gases to flow in and out freely would generate more work, (two stroke compression releases allow a cylinder to pump in and out freely creating more engine braking, and your engine turns over slower with the throttle open than it does with it closed.)

Grist for thought

Doug L

The problem with 'wet sumping' doesn't seem to be limited to vintage British machines. I came across this picture of a RSK Porsche.

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From: MoPerfServ@aol.com
Date: Sat, 20 Apr 1996 09:45:36 -0400

At the AETC (SuperFlow) conference in '95 one of the attendees was asking about oil pressure loss in heavily evacuated crankcases.....


Bob,
Have you posted on this recent thread where people are showing pictures of their shops? If you can not only remember but actually retrieve an email from 1996 your parts and tool organization must be impressive.

Brendan

Brendan S said:

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From: MoPerfServ@aol.com
Date: Sat, 20 Apr 1996 09:45:36 -0400

At the AETC (SuperFlow) conference in '95 one of the attendees was asking about oil pressure loss in heavily evacuated crankcases.....

Click to expand...

I might think that this would be evident in a dedicated wet sump system but I can't see how with a Norton Commando.

It makes sense that if you provide negative pressure in the cases that oil would flow more freely to that location. Sort of like keeping your blood pressure down by keeping your arteries clear. Less work for the pump.

However, I don't think that this is the aspect that helps solve oil leaking. It is just another benefit.

Thanks Bob for providing those discussions. Now I can say that I HAVE seen it discussed.

Russ

I figured it a little passive evacuation was good then active even better...

Small aircraft exhaust extractor article and measures.
http://www.skydynamics.com/Information/ ... g12-19.pdf

rvich said:

Thanks Bob for providing those discussions. Now I can say that I HAVE seen it discussed.
Russ

Click to expand...

Russ,
It really is a great thread. Michael Moore and Charles Falco are pretty big hitters in the in the vintage resto and racing scene. Michael runs the mc-chassis list on yahoo. Charles Falco was one of the co-curators on the Art of The Motorcycle exhibition at the Guggenheim. One thing that came up in the thread was Grumpy Jenkins' book, The Chevrolet Racing Engine. Gordon Jennings said someplace that it was one of the best primers on engine building and tuning ever. (C.R. Axtell used to call Gordon Pi Cubed ) It covers a lot of things that relate to Commandos, like the effects on performance of ring gaps, crankcase vacuum, rod length ratios, ect. When you finish it you can see where he got the nickmane.


http://freeshopmanual.com/forum/viewthr ... read_id=53

http://www.amazon.com/Chevrolet-Racing- ... py+jenkins

Duplicate Post

Bob,
I looked at the Amazon link and was about to post that they don't give those away, but then I looked at the second link and by the gods, they DO give them away! I guess that if I wasn't always in the shop covered in grease or sawdust (both is a bad combination but not unheard of) I would have already read some of this stuff!

I have downloaded the PDF and will be printing it off (most likely at work :wink: ).

Russ

rvich said:

Bob,
I looked at the Amazon link and was about to post that they don't give those away, but then I looked at the second link and by the gods, they DO give them away! I guess that if I wasn't always in the shop covered in grease or sawdust (both is a bad combination but not unheard of) I would have already read some of this stuff!

I have downloaded the PDF and will be printing it off (most likely at work :wink: ).

Russ

Click to expand...

Russ,
I didn't check the price on Amazon very carefully when I sent the post. When I was deleting the Amazon link I caught a look at the price and couldn't believe it. Then I tracked down the other link and I couldn't believe that either. Go figure.