If I understand correctly...

o0norton0o said:

Well, I'm glad that you are getting away with it when it happens occasionally.

You probably should think about doing the O-ring trick that Jim Schmitt suggests to prevent any chance of crankshaft seal displacement.... If you buy the correct O-ring, next time you take the front pulley off, you add the O-ring and it's a little insurance against the seal blowing out...

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I’m not in a hurry to try the o ring idea. In a dry primary I’d be concerned it could rub on one part or the other and possibly cause more harm than good?

grandpaul said:

YES, if you are referring to an aftermarket reed valve type breather, and NOT simply an automotive one-way ball & spring type PCV valve in-line on the OEM oil breather line.

BE SPECIFIC, because more than one aspect of the above reply can get misinterpreted in other people's comments relating to "PCV" valves!

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Lineslinger said:

I had discussed this briefly with Matt R. during rebuild and he noted that with my setup drain the CC before cranking. I assumed I had this pressure thing analyzed but wanted to ask others. I have PCV outlet line off the timing chest leading to a Mikes XS reed valve between the outlet and below the oil tank on a 74' 850. Never an issue on my automobile engine builds but different configuration methinks.

I have never tried wet sump start on Norton engine. My bike sits for long periods when hot or cold weather prevails without marking the shop floor. I spent a lot of time on rebuild making it that way. I shouldn't even be talking about it, I'll jinx it.

So, unless the PCV is set up lower crank case like a Commonz/cNw/NYC offering the pressure would and maybe could bite me with my current configuration.
I'll just keep dropping down to drain it, no big deal. Sometimes I can grab a quick nap while doing so.

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Fast Eddie said:

I’m not in a hurry to try the o ring idea. In a dry primary I’d be concerned it could rub on one part or the other and possibly cause more harm than good?

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I also run a dry primary. There's about .010" or .020" clearance between the O ring and the oil seal. Haven't seen any worrisome wear on the oil seal from rubbing so far. The O ring is there to keep the oil seal from turning inside out or from stretching and splitting due to wet sump pressure. The Oring needs to be Viton or it can dry out and crack.

Lineslinger said:

I had discussed this briefly with Matt R. during rebuild and he noted that with my setup drain the CC before cranking. I assumed I had this pressure thing analyzed but wanted to ask others. I have PCV outlet line off the timing chest leading to a Mikes XS reed valve between the outlet and below the oil tank on a 74' 850. Never an issue on my automobile engine builds but different configuration methinks.

I have never tried wet sump start on Norton engine. My bike sits for long periods when hot or cold weather prevails without marking the shop floor. I spent a lot of time on rebuild making it that way. I shouldn't even be talking about it, I'll jinx it.

So, unless the PCV is set up lower crank case like a Commonz/cNw/NYC offering the pressure would and maybe could bite me with my current configuration.
I'll just keep dropping down to drain it, no big deal. Sometimes I can grab a quick nap while doing so.

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IMHO, a PCV valve does not provide the same service as a reed valve at or near the bottom of the engine. The PCV valve reduces the air pressure in the crankcase but does nothing to quickly clear the oil. With a reed valve, every downstroke of the pistons pushes a good bit of oil out of the crankcase. The PCV valve only pushes air. So, when the engine starts it is fighting oil for much longer with an air-only breather.

It takes 5 minutes to empty the sump and no sump thread damage with the Andover Norton sump filter with small drain plug.

I still have a slight guilty feeling when I pour the oil into the tank, as it hasn't gone through the oil filter, just straight from the sump. I always check the magnet on the small plug and leave about 1/4" of oil in my catch pot (the dregs!). So far, nothing notable on the magnet or in the dregs. But doesn't feel good practise to bypass the filter. Perhaps ought to cut a filter open and rig up a filter I can pour the oil through. Bit anal tho'!

Mart UK said:

It takes 5 minutes to empty the sump and no sump thread damage with the Andover Norton sump filter with small drain plug.

I still have a slight guilty feeling when I pour the oil into the tank, as it hasn't gone through the oil filter, just straight from the sump. I always check the magnet on the small plug and leave about 1/4" of oil in my catch pot (the dregs!). So far, nothing notable on the magnet or in the dregs. But doesn't feel good practise to bypass the filter. Perhaps ought to cut a filter open and rig up a filter I can pour the oil through. Bit anal tho'!

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Agreed, but not everyone has the big sump plug, not everyone has the one with a drain in it, and removing the small plug repeatedly will likely someday make for a bad day.

When I do drain the sump, I let it sit a few minutes, then pour slowly and don't pour in the last ounce or two that has sediment (probably overkill).

You can use a coffee filter in a funnel, but it is pretty slow to put the oil back.

If I have a reed valve and a standard primary on a pre-MK3, I just start the bike. If one ever blows the seal - well, that's not very hard to replace.

I have found my timing chest breathers to be EXCELLENT in practice, and inexpensive. Oil found passing thru them will only be in light mist form, and headed into the oil tank anyway. I used to sell them for $25. I think I still have a pair of them...

I like that configuration. Very straight forward.

marshg246 said:

So, when the engine starts it is fighting oil for much longer with an air-only breather.

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The engine is "fighting oil"... The only issue where fighting oil resistance might be negative is that the oil might slow down the crankshaft when you kick the bike over making it harder to start. Other than that, a good splash of oil within the crankcase will splash oil on the cam, the underside of the piston, and the cylinder walls. I think both of those are a good thing during start up after a prolonged period without being run.

People always mention PCV valves. I also don't know what sort of mechanism that entails. A reed valve works because it is fast acting, and the mass of the reed is very small so it can cycle at very high speeds. I've seen people say they can use a metal ball valve, but the physics of it don't suggest it would work at high RPM's because the ball has a significant mass and because of that it can't change direction quickly, like a reed in a reed valve can.

Here's my timing side breather. It looks a lot like GP's. I also have Jim Schmitt's camshaft port breather working along side my timing chest breather, and did notice an elimination of all oil leakage after I added the second reed breather...

Mart UK said:

It takes 5 minutes to empty the sump and no sump thread damage with the Andover Norton sump filter with small drain plug.

I still have a slight guilty feeling when I pour the oil into the tank, as it hasn't gone through the oil filter, just straight from the sump. I always check the magnet on the small plug and leave about 1/4" of oil in my catch pot (the dregs!). So far, nothing notable on the magnet or in the dregs. But doesn't feel good practise to bypass the filter. Perhaps ought to cut a filter open and rig up a filter I can pour the oil through. Bit anal tho'!

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Cheesecloth is a good filter. A neighborhood fellow drove a VW rabbit diesel from Central Ontario to the BC coast on used French fry oil. He spent more time filtering than driving, but it was quite a feat. He used a total of 5 gallons of diesel fuel out of the pump to get the engine started in the mornings.