Crank case breather

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Towner said:
Hello,

I read much about PCV valves in this forum and I already discovered teh typical oil leaks at my Commando.
Normally the breather hose is connected to the air filter, but most owners (as I) disconnected it to avoid soiling the filter.
But the PCV system (positive crankcase ventilation) wasn't only introduced to avoid pollution, but also the intake suction should
take away the blow-by gases and additional generate the negative pressure in the crankcase.

So my question is:

Do the oil leaks appear because the breather hose is not connected to the air filter ?

Ralf
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No.

There is insufficient vacuum in the air box to pull useful vacuum at the other end of the breather hose.
Automotive PCV valves typically are ball valves, using a steel ball to stop an orifice. As such, they cannot react as precisely or quickly as a reed valve.

That is OK in an old worn out multi cylinder car engine with offsetting internal pressure/falling piston pulses where the problem is constant blow by that likely holds a ball valve constantly open.

Our two pistons move together, creating huge pressure and vacuum pulses. As revs rise, a steel ball valve likely beat itself up and would just flutter in response to our quick rise/fall, reversals, of pressure pulses.

A reed valve, located as close to the crankcase as possible, is the answer if you want to create an average low pressure condition in the crankcase.
 
swooshdave said:
If the breather hose is blocked off then the answer is... probably. Can't you route the breather to the oil tank?
Click to expand...

The breather hose from the crankcase is routed to the oil tank. What I mean is the hose between oil tank and air filter.
 
No.

There is insufficient vacuum in the air box to pull useful vacuum at the other end of the breather hose.
Automotive PCV valves typically are ball valves, using a steel ball to stop an orifice. As such, they cannot react as precisely or quickly as a reed valve.

That is OK in an old worn out multi cylinder car engine with offsetting internal pressure/falling piston pulses where the problem is constant blow by that likely holds a ball valve constantly open.

Our two pistons move together, creating huge pressure and vacuum pulses. As revs rise, a steel ball valve likely beat itself up and would just flutter in response to our quick rise/fall, reversals, of pressure pulses.

A reed valve, located as close to the crankcase as possible, is the answer if you want to create an average low pressure condition in the crankcase.[/quote]

An automotive type PCV valve operates from manifold vacuum. There is not steady manifold vacuum on a Norton so they are of no use.
The check valve in a PCV valve is there to prevent backfires in the intake manifold from traveling down the hose into the crankcase and causing a big boom. The valve is much too heavy to react to the crankcase pulses. Jim
 
xbacksideslider said:
No.

There is insufficient vacuum in the air box to pull useful vacuum at the other end of the breather hose.
Click to expand...

comnoz said:
There is not steady manifold vacuum on a Norton so they are of no use.
Click to expand...

I supposed that, because the air filter is relatively open.
I had a leak a the third fin, which stopped after installing the XS 650 valve near to the oil tank. But now a leak appeared at the head gasket.
So the valve does not the job as expected.
 
Towner said:
I had a leak a the third fin, which stopped after installing the XS 650 valve near to the oil tank. But now a leak appeared at the head gasket.
So the valve does not the job as expected.
Click to expand...

Well that's a rather blunt statement. You can't expect the XS PCV valve to solve ALL your problems :wink:
 
nortonspeed said:
Well that's a rather blunt statement. You can't expect the XS PCV valve to solve ALL your problems :wink:
Click to expand...

Ok , not all - but at least the problems with the leaks on my Commando :D

When I installed the valve, I had only the small leak at the nut at the third fin. I hoped, that the valve would prevent a further removal of the head.
This leak stopped, but after a few weeks a new leak appeared at the gasket gap. So I still had to remove the head. When you have to remove
the head anyway, the valve is needless. This time I applied Hylomar around the pushrod tubes and hope that this helps more than the valve.

Ralf
 
Ah so Ralf, healing words just to know how the plans of mice and men get foiled at times for all of us. Might add silk, cotton or un-waxed floss around tunnels. Hylomar from Rolls Royce aircraft, is 600'F rated but our heads better not ever see 100' of that on a racer. My last double crosser like this was oil leak d/t a primary cover front bolt backing out, fixed it and ain't ridden it since d/t KS rachet or something attached don't connect no more. I'm waiting for the mood and time to reseal with thread crank cases up and keep eye on air filtration as blow by is so so insidious.
 
Hey , maybe you have one of those famous porous heads ,I've seen a pile of them at our wrecking yard as a teenager. Distressing. :|
 
Good point, Comnoz, an automotive PCV valve is connected to the intake manifold, on the low pressure side of the carburetor slide/throttle plate (between the throttle and the intake valve) where there is real vacuum, and NOT in the air box where there is almost none.
 
Towner said:
nortonspeed said:
Well that's a rather blunt statement. You can't expect the XS PCV valve to solve ALL your problems :wink:
Click to expand...

Ok , not all - but at least the problems with the leaks on my Commando :D

When I installed the valve, I had only the small leak at the nut at the third fin. I hoped, that the valve would prevent a further removal of the head.
This leak stopped, but after a few weeks a new leak appeared at the gasket gap. So I still had to remove the head. When you have to remove
the head anyway, the valve is needless. This time I applied Hylomar around the pushrod tubes and hope that this helps more than the valve.

Ralf
Click to expand...

Ralf,
If your bike still leaks let me know. I will send you one of my reed breathers. If it doesn't fix the leak you don't have to pay me for it. How's that for a deal.
Of course my breather will not fix a leak from a high pressure source, like the rocker spindle covers ect. Jim
 
Hi Jim,

thank you very much for your kind offer. And I am sure that this is the best solution for the problem. But it is not the costs, what I want to avoid, but stripping down the cases. These minor weeping leaks at the tach drive, etc. are not that what worries me, but the head removals bother me. It should be possible to stop leaks at the head gasket without any valve (IMHO).

Torontonian said:
Hey , maybe you have one of those famous porous heads ,I've seen a pile of them at our wrecking yard as a teenager. Distressing. :|
Click to expand...
Hopefully not. I heard about this, but I can't see anything . It is a RH4 head.

Ralf
 
Towner said:
Hi Jim,

thank you very much for your kind offer. And I am sure that this is the best solution for the problem. But it is not the costs, what I want to avoid, but stripping down the cases. These minor weeping leaks at the tach drive, etc. are not that what worries me, but the head removals bother me. It should be possible to stop leaks at the head gasket without any valve (IMHO).

Torontonian said:
Hey , maybe you have one of those famous porous heads ,I've seen a pile of them at our wrecking yard as a teenager. Distressing. :|
Click to expand...
Hopefully not. I heard about this, but I can't see anything . It is a RH4 head.

Ralf
Click to expand...

You don't need to strip down the cases with Jim's sump breather. Just pop out the big hex under the engine, install lines and go.
 
swooshdave said:
You don't need to strip down the cases with Jim's sump breather. Just pop out the big hex under the engine, install lines and go.
Click to expand...

Oh, I thought it was the same as CNW offers.

@Jim: Ok, then it would be an option. I let you know if the leak appears again - could last until next year, have you some in stock ?
 
Well since our breather wouldn't fit on the back of the case, I went back to the XS650 breather inline. Here's a picture of where we mounted it. Looks OK, and actually works really well. I'd still love to got with Jims version on the back of the case, but I will need to save up a bit..

Crank case breather
 
That is a very common install in that location. I for one prefer that location, keeping the oil down away from the valve. You will find it quite functional.
Well done.
 
I bought a Krankvent,too, and ran it off the timing side. What I found out was that the vent will operate with a 3/8 hose AND NO LARGER. It immediately made improvements up to 4500 RPM, I did not run it any higher. It also keeps oil from migrating to the top of the piston. I have now ordered the CNW breather and very eager to try it.
 
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