PCV valve ?

Chester · Feb 19, 2011

Hey Y'all

'74 Mk 2A

Just going thru some past threads for some barrel and head gasket info, and PCV valves seem to come up a fair amount.

Should every Norton have one? Where do I find such a thing, and where are they mounted?

Appreciate your opinions!

rvich · Feb 19, 2011

There are two kinds of Nortons out there...those that have breather valves and those that will! Sort of like adding fiber to your diet, the exact benefits can be argued, but everybody seems to agree it is a good idea.

Here is some reading for you:

inline-breather-valves-revisited-t7637.html?hilit=breather
breather-valve-problem-t7562.html?hilit=breather
xs650-breather-exposed-t7345.html?hilit=breather
one-way-breather-valve-differences-t5929.html?hilit=breather
xs650-mount-near-tank-breather-t5866.html?hilit=breather
crank-case-breather-t3680.html?hilit=breather

I have the XS650 valve on my bike. I like the looks of the CNW unit, but the list of stuff to do has other things ahead of it.

Russ

mikegray660 · Feb 19, 2011

you can do a search - been covered extensively

rvich · Feb 19, 2011

Doing a search for "PCV" gives 446 hits, well or now 447 with this entry. Doing a search for "breather" yields over 1500 hits. It can be hard to know what you are looking for. It has been suggested before that some of these topics need to have an area where people can go to find information without playing roulette with the basic search. I don't know enough about building search engines or web sites to comment further. I was able to pull the list of suggested reading above only because I participated in them and could look through my own posts. Otherwise it would seem an endless task to weed through.

Russ

Chester · Feb 19, 2011

Thanks Russ!

I know nothing about building web sites and such. I really appreciate the info you sent.

It sounds like the xs650 is a favored breather, and that's good enough for me!!

thx again

Chester

swooshdave · Feb 19, 2011

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. It can be hard to know what you are looking for. It has been suggested before that some of these topics need to have an area where people can go to find information without playing roulette with the basic search. I don't know enough about building search engines or web sites to comment further. I was able to pull the list of suggested reading above only because I participated in them and could look through my own posts. Otherwise it would seem an endless task to weed through.

Russ

Some forums will have a special section for constantly asked questions. No matter how you configure a forum someone will come along and ask the same question. I'm not sure if this forum is big enough to support sub-forums yet.

pete.v · Feb 19, 2011

Chester said:
Hey Y'all

'74 Mk 2A

Just going thru some past threads for some barrel and head gasket info, and PCV valves seem to come up a fair amount.

Should every Norton have one? Where do I find such a thing, and where are they mounted?

Appreciate your opinions!

As you you might suspect, people are a little jaded with this subject. Let me see if i can simplify a little.

The 72 crankcase had issues with the breather setup at the back of the lower crankcase along with oil being thrown back there by the crank and the sump misplace up front. Undue pressure would build in these cases and blow oil where ever it's weakest like at the crank seal on the primary. These pc valves help with this pressure and some say that vacuum is produced easing the downstroke and adding 25 hp. Just kidding little to no added hp is produced.

With your MKIIa the breathers are in a good a place and the sump is back where it is supposed to be. This is not to say that you cannot use a pcv, it's just that the need and the benefit is much less.

Along with the "WTMI" that you find in your searches, I hope this adds some perspective.

JimC · Feb 19, 2011

All four stroke engines benefit from a crankcase with little or no air pressure. The most obvious benefit for the Commando is the lessening, if not outright eliminating, oil leaks. A secondary benefit is the reduced air resistance in the crankcase resulting in a power gain. Probably in the neighborhood of one or two HP. High performance engines are sometimes fitted with a vacuum pump to evacuate the air in the crankcase. Evidently, the gain from no air resistance is greater than the loss from turning the pump.

Hobot · Feb 19, 2011

Cheap down and dirty fits perfect and last a few seasons standard for decades...

Motormite HELP 80190

in any auto parts.

For $100 version see CNW or Krank Vent sites for Al lipstick size canister with either hose barbs or threaded fittings.

Old Brits has article on Combat oil drain fix.

Or could build an exhaust eductor.

JimC · Feb 20, 2011

I put the Motormite vacuum check valve pretty much in the category of an urban myth. At best, it provides a placebo effect. The one I tried certainly didn't reduce oil passing the crankshaft seal. The XS 650 PCV valve ($16) did the trick.

Stuart SS · Feb 20, 2011

:roll:
I have tried to relay this message for *(#$ &*() years ~ a bit like the story related to low tension/ secondary leads to points housings.. Ho hum ~

Chester

If you have researched the past posts then you will get the idea ~ Sorry but ~ All you need is a 'valve' unit which will allow pressure to be released on the down stroke , yet allow air to be drawn in on the compression stroke ~

Just use a PCV unit from a 1980/90s motor car ~ after all they are more than adequate ~ Any relief of crank-case pressure will be an asset ~ There are kits available ~ but WhyTF pay for a 'specialised' unit when a unit from a car is adequate ~

Mate ~ KEEP IT SIMPLE ~ KISS method ~ its not hard ~ 8)

caddy chris · Feb 20, 2011

+1 for the xs650 breather. $16, spliced it in the breather hose to the oil tank, up under the seat. Easy. Cheap. Hidden. Clean motor.

cash · Feb 20, 2011

I've been a breather valve fan for many years and fitted them to just about everything. However I found the XS650 valve too efficient and as Jim pointed out it can and in my case did trap oil in the timing chest. I then became concerned that the inlet rocker oil drain would be compromised so I've removed the XS650 valve and have not refitted one of my not so efficient versions.

So far so good.

Cash

mikegray660 · Feb 20, 2011

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

well doesn't that mean covered extensively...

Hobot · Feb 20, 2011

Trapping oil in timing case does not compute to me. There is a low down vent-drain hole that connects to the crank case sump so how can oil get trapped? I can see oil being pushed out the breather path, but that must mean better location and/or baffle needed, not too much low pressure in cases. I'm spoiled i guess on modified Combat- unable to get any oil to show on white glove test inside breather hose where it attached to cases. No leaks either so Deer supplied $100 Krank vent doing its job.

cash · Feb 21, 2011

hobot said:
Trapping oil in timing case does not compute to me. There is a low down vent-drain hole that connects to the crank case sump so how can oil get trapped? I can see oil being pushed out the breather path, but that must mean better location and/or baffle needed, not too much low pressure in cases. I'm spoiled i guess on modified Combat- unable to get any oil to show on white glove test inside breather hose where it attached to cases. No leaks either so Deer supplied $100 Krank vent doing its job.

Hi Steve,

This is Jim's reply to my question,

Re: Breather Valve Problem ?

Postby comnoz » Tue Sep 21, 2010 9:50 am
Cash, what you are seeing is common on reed valves connected to the timing chest. The oil that is missing from the tank is trapped in the timing chest. Return to the main cases is poor with no valve and gets worse with a valve. That is part of the reason for the location of the CNW reed valve and the modifications done to the cases. Jim
No Carbs
"If the facts don't fit the theory, change the facts." Einstein

comnoz

My Commando is very oil tight and always has been, the oil pump is in very good conditon and there's no excessive blow by .
That out of the way, with the oil tank cap removed, when I kick the motor over there's a rush of escaping breather gas and as would be expected no suction, with the motor running there's nothing either way.
As Jim says, what's happening is the timing drive is picking up crakcase oil as it should and holding it in there, and because there's very little or no gas flow at specific revs the oil cannot return or be sucked back into the sump.

Anyhow, for me by removing the valve the problem went. Perhaps I might revert to my old Guzzi loose ball. If I get back on the bike this coming season I'll know for sure.

Cash

grandpaul · Feb 21, 2011

There were misstatements made...

A one-way valve ALLOWS crankcase pressure to be released on the pistons' downstroke. This stage is where the pistons are essentially acting as a compressor, pressurizing the crankcases.

At the same time, it DISALLOWS air back in to the crankcase on the upstroke, essentially creating a low pressure (relative vacuum).

There is precious little resistance of the spinning crank to air pressure; the resistance is against the pistons traveling downward into the crankcase area, and it is significant.

Hortons Norton · Feb 21, 2011

OK, So if fitting a breather valve (XS-650) on my timing chest vent is stopping the oil from returning to the cases why have I never noticed any change in the oil level, This now has me thinking. How would I find out if it was trapped in the timing case? I had the Old Britts mod. done to my 72 Combat cases and he drills two extra holes to allow more air to pass into the timing chest. Could this be why the oil is not being trapped inside in my timing chest? The only reason I ask is because Jim Comstock would know if this was an issue, I have a bike thats oil tight and runs great, WHAT NOW!!!!!! LOL LOL :roll:

britbike220 · Feb 21, 2011

I don't understand this. Like stated the xs breather opens allowing air out and closes so air doesn't get back in. What does this have to do with oil being trapped in the timing chest and if it is a big concern, I'll go back to a stock set up like originally designed. Seems like these debates change depending on which way the wind is blowing. Today the breather is bad last month it was good. I've seen no adverse or noticeable positive effects with the stock set up or with the breather installed, but I am glad I only paid 16 bucks for my downgrade or is it upgrade.

Hobot · Feb 21, 2011

Must be some confusion on those saying 'oil trapped in timing case'. The TS drain hole is high enough to leave an oil bath the chain and gears pick up on first kicking, maybe that's what they are noticing On this note its worth while to open up the TS air vents for less pumping loss and less pressure spikes as helps increase the case volume ratio to the piston stroke pumping.

I have a bike thats oil tight and runs great, WHAT NOW!!!!!! LOL LOL :roll:

Oh I know the answer to that, ride and use it up again, then repeat till no more.

PCV valve ?

Similar threads