PCV valve ?

Once the crank is up to tickover RPM, the crankcases are at negative pressure with a good one-way reed valve. So, the size of the opening isn't critical. As long as it's at least the size of the factory plumbing, it'll do fine, any bigger is a slight plus.

The confusion here has to do with where the reed valve is located, high on the timing chest or on the crankcase.

If it's up high on the timing case - above the oil level - where the magneto once was and where the starter later went, then it will tend to create a low pressure that will tend to pull oil into the timing case, accumulate it, and hold it away from the crank case and thereby away from the oil pump pick up point. The oil tank's volume is what saves the engine from oil starvation. It is conceivable that a reed valved breather on the timing case, when it gets packed with oil, may even pump oil up and out of the timing case and back to the oil tank.

If the reed valve breather take off is on the crank case, then it will tend to pull oil away from the timing chest.

Don't know about that, The low pressure is caused by the pistons rising in the crankcase without a way for air to re-enter. When the pistons move down the pressure is raised in the cases and moves to the timing chest and through the reed valve, Once this happens a few times the cases will be slightly at a low pressure and so will the timing chest, I really don't think the timing chest could have a lower pressure than the cases. I think this is why Fred drills the holes in the timing side case to allow the air to move through the cases, This did wonders on my 75 which had little nagging weeps from the rocker cover and the third fin area. I can say this for sure, It stopped all those leaks. On the 72 I just put one on because it worked so well on the 75. It is known that at high rpm these little valves really can't keep up, My bikes rarely go much higher than 5,500 so they seem to work great for me. Of course this is just my opinion and I could just be full of S#*T but they do work. Ride safe guys, Chuck. :wink:

xbacksideslider said:

The confusion here has to do with where the reed valve is located, high on the timing chest or on the crankcase.

If it's up high on the timing case - above the oil level - where the magneto once was and where the starter later went, then it will tend to create a low pressure that will tend to pull oil into the timing case, accumulate it, and hold it away from the crank case and thereby away from the oil pump pick up point. The oil tank's volume is what saves the engine from oil starvation. It is conceivable that a reed valved breather on the timing case, when it gets packed with oil, may even pump oil up and out of the timing case and back to the oil tank.

If the reed valve breather take off is on the crank case, then it will tend to pull oil away from the timing chest.

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The PCV valve does not create the vacuum, the upstroke of the pistons does that. Have no fear of the PCV valve sucking oil from either the timing or crank cases. The vacuum source would have to be downstream of the PCV valve for that to happen.

Still can't comprehend TS case oil level or pressure build up, over the main sump. There are two holes each ~1/4" dia, one that sets oil level in TS case and another up by the cam bushing that really does some air jet work to keep both volumes trying to equalize. Street engine goal is just to lower inside PSI a bit below outside for oil weeps, racers at top rpm would get some power benefit by an active suck down to low PSI, till the crank seals must be reversed. Don't know the flapper frequency limits of the reed valves being used in Nortons, but if work in 8,000 rpm 2 strokes why not.

Tesla valveless, VALVULAR CONDUIT, to introduce fuel against turbine combustion back pressure.

Sorry for chiming in here, but did I hear somewhere that the xs650 valve does not work as well on '72s with the breather at the bottom of the crankcases, or am I crazy? I'd like to save some money and put it on my 72 now, before upgrading to the CNW a bit down the road.

Thanks

If I remember correctly Jim had said that when he designed his rear breather to the 72 cases he would not only block off that hole that leads to the timing chest, But also lowered the drain for timing chest too. He said he found the timing chest oil level was a bit high and would bring the oil in there to a higher temp because it was whipped around so much. Please remember this is all from my memory and I could be screwing this up. Also I think, and he may also have said this, The air just cannot escape through the chest and then back out at high rpm when the breather is on the timing side, and when it is on the rear it can escape much quicker without going through those little holes. Makes perfect sense to me, I also remember him saying he made a timing cover with some kind of window in it and could see the oil being whipped around. Thats what makes this forum so great, You have guys like Jim that have done all the homework, footwork and spent all the time and money to make our lives a little easier. Sorry Jim if I screwed this up, My memory is not what it once was. I'm sure you have something better to do with your time than to explain this again. How's the turbo kit coming? LOL :wink:

As I recall, the XS 650 PCV valve was said to be more effective the closer it was to the crankcase. Much as CNW has done with their valve. I mounted mine (XS 650 valve) inline, midway between the crankcase and oil tank on my 72 Combat. Stopped the oil leaks. That's what I was after.

The more case volume the less the size of pressure spikes. If a check valve works better attached to smaller volume of just the crankcase it implies its a bit tough to work with slightly less pressure spikes d/t added volume if attached near end of breather hose. I don't know reed valve limitations but I can't quite accept its location should matter much after a few rev's.

Anywho Peel had good dry success with a Krank Vent valve and three 1/2" TS case vent holes.

mikegray660 said:

rvich said:

Doing a search for "PCV" gives 446 hits, well or now 447 with this entry. Doing a search for "breather" yields over 1500 hits. I.....

Russ

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well doesn't that mean covered extensively...

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Another piece of info on PCV's Norton actuallt fitted a PC reed valve to the P10 engine (1966-1967)
(see page 20 of Mick Duckworths book on the Norton Commando) but not 100% certain this is accurate

Hi, what's about omitting the disc between roller bearing and oil pump pinion?? should allow the oil trapped in the timing case to free flow back to the main case .........(though i remember Comnoz allready replied to me not to do .....but?) otherwise was it Jean Droit or Ludwig or ... drilling another oil way hole under oil pump location to allow oil to drain back where it should be...

JimC said:

As I recall, the XS 650 PCV valve was said to be more effective the closer it was to the crankcase. Much as CNW has done with their valve. I mounted mine (XS 650 valve) inline, midway between the crankcase and oil tank on my 72 Combat. Stopped the oil leaks. That's what I was after.

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Jim,
Did you mill or drill any holes in your cases before fitting the xs650 valve? And if you don't mind, a picture of your setup would be great just so I can understand the location of the breather, if you don't have a picture, don't waste your time taking one just for me!

I didn't do any mods than other what you see here.


By jcclausen at 2008-06-13[/img]

if you don't have a picture, don't waste your time taking one just for me!

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Helping someone out is never a waste of time. One never knows when they will find themselves in need.

JimC said:

I didn't do any mods than other what you see here.

By jcclausen at 2008-06-13[/img]

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Same here fitted the PCV in the standard breather pipe cured the irriatating small leaks immediately, notably on the tacho drive.

If you run a primary belt, the PCV valve is a must. I changed crankshaft seals until I was dizzy trying to stop that leak. Installed a XS 650 PCV valve, presto! No more leaks. I recall an earlier post indicating that a seal made from unobtainium would do the trick. Wonder if that guy ever found the seal. If he did I'm sure it cost more than $16.

Sheesh, of course the upstroke creates a vacuum! just as the downstroke creates pressure. The issue is the average, steady state relative pressure. That, after all, is what the reed valve does - it creates an average low pressure/state of vacuum - by allowing crankcase gasses to go out but not to come back in.

But that is all somewhat beside the point. The point is where best to locate the take off for the reed valve. It should go where it makes functional sense, not just some convenient spot. It belongs on the the crankcase, NOT the timing chest, or, for that matter, the cylinder head.

xbacksideslider said:

Sheesh, of course the upstroke creates a vacuum! just as the downstroke creates pressure. The issue is the average, steady state relative pressure. That, after all, is what the reed valve does - it creates an average low pressure/state of vacuum - by allowing crankcase gasses to go out but not to come back in.

But that is all somewhat beside the point. The point is where best to locate the take off for the reed valve. It should go where it makes functional sense, not just some convenient spot. It belongs on the the crankcase, NOT the timing chest, or, for that matter, the cylinder head.

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It is important that when discussing altering the breather on a Commando that the year is mentioned the 1973-1974 Commando had holes opened in the timing side case into the timing chest and the a breather takeoff where the magneto used to be. I cannot see any problem with fitting a PCV valve about 1/3rd of the way along the breather pipe that returns to the oil tank. You would need a substantial pressure differential between the cranckcase and timing chest to 'hold' oil in the timing chest with the 73-74 setup. I have read the comments regarding the 71-72 Commando's tendency to force oil up the breather and that more oil was being forced up the breather than was being pumped back but thats about it as far as reading up on the recommended modifications goes except that just bunging a PCV valve into the breather line is not going to solve all the 71-72's issues with regard to the moving of the oil pick up location and other modifocations to the crankcases themselves.IMHO

My experience with my 72 Combat was plumbing the PCV valve did solve the issues I was having. Leaks. As for excessive oil in the breather line, that was never a problem on my bike. Putting a PCV valve in the breather line will not exacerbate any oil breather problems that might exist. If anything, having no pressure or even a vacuum in the crankcase would lessen the chance of oil going out the breather hole.

marinatlas said:

Hi, what's about omitting the disc between roller bearing and oil pump pinion?? should allow the oil trapped in the timing case to free flow back to the main case .........(though i remember Comnoz allready replied to me not to do .....but?) otherwise was it Jean Droit or Ludwig or ... drilling another oil way hole under oil pump location to allow oil to drain back where it should be...

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This is the hole that drains oil from the timing chest to the crank. This should also be considered as the proper oil level in this area and should not be messed with. This casted channel can be see externally and shows the downward angle for drainage. This is a good size drain hole and see no reason to be concerned for either pressure or vacuum having an effect on the oil lever here.


Last season i took a hunch and "added" another breather at the mag boss area. With 2 breathers I suffered no pumping loss and felt no difference at 95+ mph, 6000 ish rpm. In addition, the pressure from both breathers seemed equal. I don't know if this is helpful or adds confusion. I have machine a set of late 72 cases per Old Britts, closed off the lower left vent and added a grandpaul reed to the mag boss. Waiting for weather.
HEY CHESTER, You still with us? Chester be long gone!