Reed type PCV Valve

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I checked out the Eurospares link. Very interesting. One thing is very clear, some people don't know much about an internal combustion engine but are convinced otherwise.

If you read the link it should be abundantly clear why the Commando needs a PCV valve. I chuckle when some Norton owners who refuse to run a PCV valve, but continue to seek a magic crankshaft seal to stop the oil from leaking into the primary. Installing a PCV valve should be the first thing you do to address oil leaks.
 
JimC said:
I checked out the Eurospares link. Very interesting. One thing is very clear, some people don't know much about an internal combustion engine but are convinced otherwise.

If you read the link it should be abundantly clear why the Commando needs a PCV valve. I chuckle when some Norton owners who refuse to run a PCV valve, but continue to seek a magic crankshaft seal to stop the oil from leaking into the primary. Installing a PCV valve should be the first thing you do to address oil leaks.
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I still don't agree with the way Fred moved the 72 breather to the timing case. The 72 style breather is basically an open hole, you need a reed valve or the like for the engine. Although you will may some benefit from running the breather to the intake manifold. I don't see how you can get any vacuum going to the oil tank.
 
I, too, think it's a mistake to vent to the timing case. It wasn't just Fred of Old Britt's to do this. I believe this is how the stock 850 is configured. Jim Comstock's research with PCV valves showed placing the valve closest to the crankcase is best.
 
Hortons Norton said:
I think Fred installed a one way valve inside the 72 breather, No?
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Reed type PCV Valve


Yeah, but it's just the Motormite valve shoved in there. As a simple flapper and as discussed above, it is no substitute for a reed valve.

I need to recheck dimensions but I'd like to see if the BMW or Ducati reed valves will fit in the stock breather.
 
Dave, the Ducati PCV is a reed type (see pictures earlier in this post) the thread is about 40mm diameter.
I made an adapter so it fits inline in the breather hose just behind the air cleaner. (between engine and oil tank)

Haven't tried it yet, but I will this weekend.
 
See the bottom of the first page of this subject, or do you mean a picture of it on the bike?
 
One thing to remember is that a pcv valve only really opens and closes at lower rpm, I'm refering to std automotive types with a metal disc and spring, at higher rpm the valve stays open and breaths straight into the manifold. The reed valves must be able to work at a much higher rpm to have any effect.
 
splatt said:
One thing to remember is that a pcv valve only really opens and closes at lower rpm, I'm refering to std automotive types with a metal disc and spring, at higher rpm the valve stays open and breaths straight into the manifold. The reed valves must be able to work at a much higher rpm to have any effect.
Click to expand...

Note that BMW replaced the disc type valve on their bikes with a reed one.
 
GRM 450 said:
Dave, the Ducati PCV is a reed type (see pictures earlier in this post) the thread is about 40mm diameter.
I made an adapter so it fits inline in the breather hose just behind the air cleaner. (between engine and oil tank)

Haven't tried it yet, but I will this weekend.
Click to expand...

How big is just the reed valve (if you can separate it from the housing)? I'm trying to see if it will fit in the 72 breather.
 
Davamb,

Reed type PCV Valve


Reed type PCV Valve


It's a bit hard to see where it is but here you are.

swooshdave, if you see the pics of the thing apart (on page 1) the reeds are about 10mm wide x 25mm long and there is 2 of them.
There is also a small hole about 1mm, I would assume this is to equalise the pressure when the engine is turned off and maybe to let any oil run back into the engine? This can be blocked if neded.

graeme
 
splatt said:
One thing to remember is that a pcv valve only really opens and closes at lower rpm, I'm refering to std automotive types with a metal disc and spring, at higher rpm the valve stays open and breaths straight into the manifold. The reed valves must be able to work at a much higher rpm to have any effect.
Click to expand...
An automotive engine doesn't produce much in the way of pulses. In nearly all of them when one piston goes up another one is going down. The valves are there to make sure that the overall flow is in one direction. The ones I've seen people use on bikes are the AV type that are a rubber diaphragm. Someone told me once that the case reed two strokes have been observed with highspeed photography to go wonky at a certain rpm then just stay open. I'd bet any valve; disc, reed, plunger, or flapper is going to do the same.

The eight hundred pound gorilla in the room that can't be ignored, no matter what type of valve, is where you put it. This is an air pump that relies on clear pulses to work. With an engine vented out the timing cover, the air in the crankcase has to be compressed and shoved through the holes in the case to the timing chest. The air in the timing chest has to be compressed then go through the hole in the back into a hose. The air in a the hose has to be compressed before it reaches the valve. It's the peaks at the valve that do all the work and the air all along the way is acting like a spring. It's not hyraulic fluid. All of those chambers and holes and tubes are going to buffer the signal to a whisper that may not be able to break through the threshold of the valve, in which case maybe it would be better not to have any valve at all. The CNW valve is in the best place to have a chance to do the job. Perfect doesn't have to be the enemy of good and I wouldn't tear an engine apart to put Matt's valve in, but I would try to put the valve as close to the engine as I could get it.
 
JimC said:
I checked out the Eurospares link. Very interesting. One thing is very clear, some people don't know much about an internal combustion engine but are convinced otherwise.
Click to expand...
Jim, I'll bet you're talking about Charles Falco. That was some flight of fancy there, but he is a theoretical physicist. He chose the bikes for the Art of the Motorcycle exhibits. He does know engines and was the perennial 12th grader in a one room schoolhouse over at BritIron for a long time till he left in a huff calling someone a Global Village Idiot. It was't me, I tended to lurk back then :D

swooshdave said:
How big is just the reed valve (if you can separate it from the housing)? I'm trying to see if it will fit in the 72 breather.
Click to expand...
Dave, would that be perfect or what? :!:
 
Dave, sorry, I see what you mean about pulling the valve apart and fitting it to your existing valve.
The valve I used screwed into the rear of a Ducati crankcase, I just made an adaptor to use it inline. (MK3)
You could pull it apart and remove the black plastic piece with the reeds in it (if you wanted to) and cut the plastic down to a smaller size. How small and what shape ??????? I don't know. Good idea though.

This valve opens with very little puff, so, although I agree air has a springy compressable nature, I hope it has enough push with 2 pistons falling together to open the one way valve then the next up stroke should create less pressure in the crankcases. Then the next down pushes a little more out, etc etc. (assuming good ring and guide sealing) The end result should be less crankcase pressure and less oil leaks.

I've built motors before, not english, and they don't leak. The pcv makes sense as all the Italian motors had pcv's as standard. Even ones older than Commandos.
Time will tell.
graeme.
 
Jim, I'll bet you're talking about Charles Falco. That was some flight of fancy there, but he is a theoretical physicist. He chose the bikes for the Art of the Motorcycle exhibits. He does know engines and was the perennial 12th grader in a one room schoolhouse over at BritIron for a long time till he left in a huff calling someone a Global Village Idiot. It was't me, I tended to lurk back then
Click to expand...

I didn't have a problem with Falco. I was dumbstruck by the flat earth guy who referred to the Edsel, Spruce Goose, Titanic and Clear Pepsi. Then there was the guy who said atmospheric pressure kept oil in his engine.

There are those who seem to think if the Norton needed a reed type PCV valve it would of come with one. You can always tell them by the leaking, oil covered bike they ride. One advantage to not having a PCV valve was I never had to oil my boots.
 
bpatton said:
Someone told me once that the case reed two strokes have been observed with highspeed photography to go wonky at a certain rpm then just stay open. I'd bet any valve; disc, reed, plunger, or flapper is going to do the same.
Click to expand...

Yeah, but I bet the reed is going to work better at higher rpm than any other valve-type.

The eight hundred pound gorilla in the room that can't be ignored, no matter what type of valve, is where you put it. This is an air pump that relies on clear pulses to work. With an engine vented out the timing cover, the air in the crankcase has to be compressed and shoved through the holes in the case to the timing chest. The air in the timing chest has to be compressed then go through the hole in the back into a hose. The air in a the hose has to be compressed before it reaches the valve. It's the peaks at the valve that do all the work and the air all along the way is acting like a spring. It's not hyraulic fluid. All of those chambers and holes and tubes are going to buffer the signal to a whisper that may not be able to break through the threshold of the valve, in which case maybe it would be better not to have any valve at all. The CNW valve is in the best place to have a chance to do the job. Perfect doesn't have to be the enemy of good and I wouldn't tear an engine apart to put Matt's valve in, but I would try to put the valve as close to the engine as I could get it.
Click to expand...

Could not agree more.
 
bpatton said:
swooshdave said:
How big is just the reed valve (if you can separate it from the housing)? I'm trying to see if it will fit in the 72 breather.
Click to expand...
Dave, would that be perfect or what? :!:
Click to expand...

Well, it would be ok. I'm sure Jim's testing showed that the reed he chose was more optimal and from the looks much bigger than anything that could fit in the stock housing. So a smaller one will be less effective but should hopefully still do the job.
 
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