XS 650 PCV valve on a MKIII

If we are talking about anything other than a 72, I would say lower crank would be just fine. But I believe that the nature of the sump intake being forward and a proven flaw in racing condition, oil can accumulate and flood the breather, hence the need for a higher mounting of the reed valve. My analogy is blowing on a sax with a mouth full of 50w.

Remember, I'm talking 72 here. I have done the moderation to allow for breathing to the timing chest, opening the sump tunnel to the rear of the case, closing up the front, and milling out the baffle to allow the oil to not accumulate at the lower rear breather. I have a reed mounted on the mag area and it works just fine.

You may ask "if you have a reed mounted on the mag boss, then why mill the baffle out." Well if one reed is good, then why not two? I am not concerned with any minute amount of vacuum that may or may not be attained, but the relief of pressure without reintroducing any air to the system seems what we are really after. So, I have 2 reed breathers.

I am an opponent of mounting a reed to the bottom of a 72 breather mount without modifications to relieve the accumulation of oil in that area.

One thing is for sure, there are less generalities between model years then we think. What is good for one is not necessarily good for the other.

Jim, that is awesome.

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comnoz said:

I would not recommend a breather from the cylinder head. All the air that needs to be vented comes from the crankcase. [ring leakage] If the breather is on the head then that air needs to go up the pushrod tunnels and head drain passage to get there.

Since the oil drainback from a Norton head is pretty well restricted in size you do not want air going in the opposite direction to the oil to hinder it's return to the crankcase.

If you can't connect directly to the crankcase with a reed breather then the next best place is the timing chest. You will not get much case depression but you will vent the excess pressure that way.

Of course you could always drill and tap a hole for a hose nipple and put the breather here as I did on the 1007. There was not room on the lower rear of the engine for my regular breather. Any breather directly from the crankcase will need to be returned to the oil tank as there will be some oil vented with the air. Jim

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I don't want to start an argument here, but the pushrod tunnel cross-sectional area is much greater than the oil return passages area.....thus the counter flow in the oil passages should be minimal. I have modified my XS valve to thread directly into the timed breather port on the Atlas, the idea of a tap into the rocker box is to get the drainage, as well as eliminating the inlet tube.

The area around the pushrod tubes is large but the area around the lifters is not. I have seen racers that tried venting from the head and ended up with a flooded head and a serious smoke trail.

I don't understand what you want to do to the Atlas head. The only tube to an Atlas head is the oil supply to the head. The oil return is via the pushrod tunnels into the crankcase and through the small drilled passage from the inlet rockers that goes into the timing chest. I am not sure what "inlet tube" you are wanting to remove or how you could get by without it.

Installing a reed valve on the timed breather is of no benefit. The cam breather is already timed to open and close at the correct time. It's only problem is the tiny hole through the cam is not large enough to carry the volume of blowby created by an engine that has some miles on it. Adding a reed there will not help that problem. Jim

I just drilled the Combat baffle plate some and opened TS side bottom a bit to expose case drain, as baffle only goes to seam and oil can drain as well with or w/o the baffle in place. Wonder if a manifold pulse driven diaphragm pump might suck it down enough to mount remotely away from the cases. Maybe even a small 12 v air pump?

http://www.amazon.com/biOrb-12-Volt-Air ... b+air+pump

comnoz said:

The area around the pushrod tubes is large but the area around the lifters is not. I have seen racers that tried venting from the head and ended up with a flooded head and a serious smoke trail.

I don't understand what you want to do to the Atlas head. The only tube to an Atlas head is the oil supply to the head. The oil return is via the pushrod tunnels into the crankcase and through the small drilled passage from the inlet rockers that goes into the timing chest. I am not sure what "inlet tube" you are wanting to remove or how you could get by without it.

Installing a reed valve on the timed breather is of no benefit. The cam breather is already timed to open and close at the correct time. It's only problem is the tiny hole through the cam is not large enough to carry the volume of blowby created by an engine that has some miles on it. Adding a reed there will not help that problem. Jim

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Thanks.....as usual your posts are very informative. I did not know of the small passages at the base of the pushrods tunnels.

The "inlet tube" I wish to eliminate or minimize the length of, is the tube from crankcase, or wherever the tap is, to the reed valve. Johansen's installation is ideal, and your tap of the crankcase ideal.....others I have seen on this thread must have anywhere from 6 to 10 inches of lead-in tube, (perhaps more for those reporting mounting on the backbone) which I believe is detrimental, and which it has been noted on this thread, you also advise against.

I know the timed breather on the Atlas is supposed to work like the reed valve.....I do not think it is very effective, and Norton might have retained it if it were. In any event, I am in the process of putting in the reed valve at the timed port, and will report before and after pressure data. Isn't that how we help each other on this forum?

Thanks again for your info on tapping the rocker box cover...I think I will abandon that idea, and just obsess over oil draining back to the XS valve and fouling it. If it proves to be effective in controlling leaks, I can periodically clean it.

OK now I understand what you were trying to accomplish.

I suspect you have seen the sump plug breather I have available. That will fit an Atlas also with no mods. Then you can just cap off the timed cam breather. Jim

comnoz said:

OK now I understand what you were trying to accomplish.

I suspect you have seen the sump plug breather I have available. That will fit an Atlas also with no mods. Then you can just cap off the timed cam breather. Jim

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OK....if the XS valve at the breather port proves ineffective, I will try your sump plug breather.

slick

What do you do if you have a starter where you all are showing the PVC mounting? 1975 850 MKIII Electric Start

Duh ya live with more blow by chance as Norton issued em to leak or modify some other area for a reed or go backwards in breather evolution and use a more remotely located less efficient but likely still sufficient one in breather hose.

Xs valve will work just fine up near the oil tank. Close to the crankcase optimum but mine is just before oil tank entry and works a charm. If you are wailing about on that MK111 or racing it then it would be best closer. Puff-puff.