Non-return does it work?

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Mar 19, 2005
I have a new leak on the motor and consequently a few questions....

Strange leak, as it is located at the top of the motor housing, on the almost flat area below the carbs. Not on the bottom, like any self-respecting leak, but rather where it can only be caused by either too much internal pressure, or by the oil that must get thrown up into that area when the crank is spinning. It seeps gradually out of the place where the cases are split, just in one small area. Makes enough of a mess to run down the cases and end up on the floor, but not enough to worry about, running wise. I have read about the PCVs some of you have fit, and though the local parts fellow looked at me as if I was loco...I will somehow find one and give it a try. Maybe if there isn't a hugh amount of oil in the sump, it won't clog the PCV....
The machine wetsumps, that is not a question, and I know I could fix the leak by doing a new gasket, but I have zero interest in that as I have never had the cases apart, not in 34 years, and I'd rather not mess with them. This problem also might get into trying to cure the wetsumping, I can do the oil pump "bump and grind" and I most likely will....but I am interested in the idea of a non-return valve too. Just have grave concerns about them. Does anybody know how, exactly, they work? How are they constructed, inside? Just doesn't make sense to expect some valve to allow oil to flow downhill when the motor is running, and then to also stop it when the motor is not running. Is this valve opened by the suction action of the pump on the oil coming from the tank? I would think there would be no suction, but that the pump would be rather fed by gravity, but it has been a while since I've had a pump apart and I am not up to date as to how they exactly work. If the valve depends upon suction to open, then the condition of the pump would affect if the valve opens or not. A spring strong enough to close the valve and stop oil when not running, would require a strong pump, to open it when running. If the pump is not up to sucking the valve oil. No smiles. Sounds all mightly prone to failure if some one part of the setup is not quite up to snuff.

So.....who can give me a low-down on how these things actually work, and if they are actually safe? Any input welcome, and if someone knows how to perform magic on that ever so kind and lend me your wand....... :wink:
These valves are just a spring loaded ball valve opened by pump suction
(anyone know of any other types?).

Have a read of the following info from the NOC website regarding non-return valves:
>Technical>Commando>Wet sumping - anti-drain valves.

Also see Norvil info:
>Tech Talk>Oil Issues-18. Wet Sumping Solved.

Is it really worth it, as the valve only masks the true problem that the pump probably needs lapping?
A slack pump can also cause a loss of oil pressure, so there's two reasons for doing it!
Thanks...looks like I will be doing the pump soon. I did notice that when I dropped the oil on Thursday night (11 PM) after a ride, the sump had at least a cup in it, maybe more. Rather surprising, after all I have been hearing in the forum, about those of you that have been draining the sump before rides and you being worried about a half cup of oil being in there after a week..... :lol:

Maybe the pump isn't pulling the oil out of the sump so well too, even during a ride....could be an oil bath in there that throws it out of that tiny leak in the case I mentioned. So.....pump it is, and maybe PCV...anybody got a source for those that I could use..? Thanks!
Once the engine has stopped running, a certain amount of oil will continue to drain from the valve gear, timing chest and crankcase walls etc. so I would expect to get about that amount out of the sump!

But how much drains down per day/week?


By the way you'll never guess what I've been messing about with today!

Non-return does it work?

= Spare pump I got from eBay!!!
If you look at the brass base cover you see one of the causes of wet sumping, those nice circular patterns allow the oil to get by the gears, one of the jobs in an oil pump recondition is to restore the cover to a nice flat blemish free surface.
Just as a point of interest regarding wet sumping,my 850 used to lose most of the oil tank capacity into the crankcase in about 10 to 12 days,I did the usual pump lapping routine,this worked up to a point,it took about 4 weeks to lose a couple of pints into the c'case.The most effective "fix" that I have found is the one described in the INOA Tech. Digest,i.e. modify the existing oil gallery fed by the pump,a 5/16 drill is used to open up the gallery drilling to a depth of .575" from the flat face of the existing hole ( wrap a piece of tape around the drill bit .575" from the point as a depth gauge),clean out the hole after drilling!!. Fit a compression spring of .575" free length and .260" diameter,place a 1/4" dia. steel ball ontop of the spring.To refit the timing cover insert a drill bit through the side port that feeds the rockers,the drill bit will keep the ball and spring compressed until the cover is in place,remove the drill bit and the ball,under spring pressure,will seal off the pump outlet until the motor is started.I did this mod. 3 years ago and have had no problems,over a 5 month Winter lay up no oil is lost from the tank.It helps that I use 40 / 50 weight oil also.Good luck, ride safely. James.
kommando said:
If you look at the brass base cover you see one of the causes of wet sumping, those nice circular patterns allow the oil to get by the gears

Actually the end plate looks a whole lot worse than it is!
This was posted to another list several years ago by Ben English in reply to a post.

Reed "reedotus" Kyrk wrote:
<< Now in practice, on my 1975 Interstate, I'm going to cut the hose from
the back of the timing chest to the oil tank, and insert a one-way valve
such that under positive pressure (pistons going down), the crankcase vents
out through the valve, but the valve closes when the crankcase is under
negative pressure (pistons going up). Suggested valve is Motormite 80190
power brake check valve. >>

Yup, you got it. Frank Forster also recommends a Volkswagen part 191 611
933, but I have no experience with that.

<< And if I've got an enhancement to this correct, a hose barb is inserted
into the hose leading from the timing chest to the PCV valve. From this
barb, a vacuum line is run to the intake manifold, with a Carquest DCV1
Distributor check valve plumbed into it. >>

Whoa, now you are off into some exciting territory. This scheme was
developed by Bob Patton (who I think is on the NOC list at present) and
Steve Schoner (who was on the Brit-Iron list years ago). I tried it back in
2002 and it did work okay- the most remarkable effect on my bike was that
the extra air sucked into the intake boosted my fuel mileage by 20%. It
was kind of self regulating, as the proportion of additional air must have
been less and less as the throttle was opened due to the tiny hoses simply
not flowing much. But I don't know that I fully endorse it as a fully
proven development.

<< Apparently the intent is to add some additional manifold vacuum, although
it is unclear to me what issues or conditions this is meant to address. >>

With the one way valve, you are passively working to de-pressurize the
crankcase. Bringing manifold pressure into play moves you to an *active*
method. Other active means are exhaust suckers (welding a fitting on the
exhaust pipe where a negative pressure is expected and piping it to the
breather), or an actual electric pump.

Ben English

I had the ball check valve installed by a company that I have forgotten the name of and it did very little if any good.

hewho, have you tried cleaning the pressure release valve as this may be cloged therefor making the motor release it pressure somewhere else and finding the weak point in the seal wich is causing the leak.
crankcase pressure mods

Hewho: If you go in to work on the oil pump, you might consider creating more breathing passage for the 'cases. At some point the factory opened up more air passages in the timing side of the RH crankcase. Consider drilling more holes or enlarging existing ones. Don't cut into webs or ridges, as they provide strength and stiffness to the case. avoid leaving sharp edges, as they encourage cracks to start.
Even if you don't do that, I would still recomend adding some breathing capacity out of the engine. In the rear of the timing cover area, (under the carbs) the early engines had a steel plate covering a large round hole in the back side. Later ones eliminated the hole and plate. (this hole used to fit a magneto or points assembly) Use this area to plumb some breather hoses. You can do two or three with PCV valves. Use as big diameter hose as possible, so it can flow air with least restriction. You can dump these hoses into the air cleaner, oil tank, or into a catch bottle, or combination. Just don't run them like dump or draft (vent) lines, since there will be some oil mist that will collect in the hoses and end up on the bike, rear tire, etc...
Use a vacuum as you drill to collect the aluminum bits. You can use a piece of copper tubing taped to the vacuum hose to get inside the holes after drilling. If you have the large drain plug that helps to get the bits at the bottem. Pour solvent (kerosene, etc.) through the holes to flush the cases. Collect this and pour it thru several times. Might have to tilt the bike some. ( of course this is much easier if the engine is apart for rebuilding! )
L.A.B. said:
These valves are just a spring loaded ball valve opened by pump suction
(anyone know of any other types?).

Have a read of the following info from the NOC website regarding non-return valves:
>Technical>Commando>Wet sumping - anti-drain valves.

Also see Norvil info:
>Tech Talk>Oil Issues-18. Wet Sumping Solved.

Is it really worth it, as the valve only masks the true problem that the pump probably needs lapping?
A slack pump can also cause a loss of oil pressure, so there's two reasons for doing it!

Isn't that just a PCV valve?
rocketdoc said:
Isn't that just a PCV valve?

'PCV' valves and 'anti-drain' valves are both essentially (I suppose?) one-way valves although they serve different purposes, and the oil flows through the anti-drain in only one direction anyway, the purpose of it being to automatically stop the flow when the engine stops, and not block any reverse flow unlike a PCV operated by positive air pressure, and the anti-drain by suction (or neg. pressure?) the spring preload setting needed to allow the anti-drain valve to open and not cause any restriction to oil flow would (I guess?) need to be fairly critical so are normally designed for that purpose and also the connection to the oil system:
Hewho.....These valves work great if you don't have any other oil return issues like worn bigends (they don't have to be knocking!) where at 4000 + more oil is dumped into the cases than the oil pump can handle. That was my problem with the old Combat motor which PO had modified with the three timing case holes and 850 style breather. Well that never worked because the 72/73 Combats had the return pickup moved to the front of the cases and getting rid of the lower case breather meant all the returning oil had to be handled by the pump (what a surprise...isn't it meant to do that?). At high revs....well not necessarily that high, the oil collects at the rear where the old pickup used to be and where it went back in 73/74. That's why you hear stories about the Combat breather returning more oil to the tank than the pump. That's probably an exaggeration but it could have helped take some oil out of the sump. the only modification that properly works with the 850 breather is to block up the front pickup and machine out the rear drive side case.

All that is a long winded way of saying I had the same or worse problem as you. Tighter bigends would probably have masked the problem and let me run at 4k and 70mph (110kph) but in the end I did the drive side mod and added a Norvil 1/2" valve. That engine was dry as a bone externally until a newish rod bolt let go a few thousand miles later and grenaded the old girl. However I think that was possibly the result of running with a full "wetsump" and no oil pressure, quite a lot of the time without my knowing it! (before the pickup mods). It would empty the tank in 10-20 miles!! and it took a few runs before I realised what was going on.

The 750's were well known for leaks around the rear cyl base. according to NOC Commando notes but mine always peed out the front n/s stud.
I would always fit a breather valve, it just makes so much sense even with a properly functioning oil return system. Just think about the air that is pumped out on the downstroke does not get sucked back in again. With blowby even on good ring seals the engine needs all the help it can get.
Thanks everyone!
Still trying to digest all this info and to figure out just what I will be doing. First off will perhaps be the pump, depending if I find one of those donut shaped seals for the pump. I will search for a PCV too, but have little faith I will just walk into a store and walk out with one...but maybe.... :p
Popping the timing cover off will let me look at the timing chain and the rubber coated adjuster in there, and do a recheck on the timing too, which may be off in left field as I have always done the old, mark and replace with the rotor when I had the case open, and actually never have timed it since 76 or so. Since then I have replaced the black box two times and such, so even they may have had different specs, compared to the original. Might be better to just plop the oil back in, and in a couple of days do a timing check BEFORE I pull the timing case off so I can see if the timing was actually still in specs. Then I can do all this stuff at once when I am sure I have the donut and gaskets, seal I need....
Timing might indeed be off as the machine just doesn't have the "oompff" it had when new. Used to have a "powerband" at about 5 grand that was a real noticable thing. Not any more, although the cam looks still good. Just not looking forward to the timing of the lady......5 grand is not a neighbour pleaser... :wink: That's why I have put it off for so long...and the fact that you have to find a couple fellows to hold her down while you dial in the pickup plate. Will do to be done.
Decided to avoid a non-return valve...too dicey for me. The lady has done a lot of miles with me and it would be a shame to risk having her blow up because I was too lazy to lap in an oil pump.... :wink:
Bigends/oil pressure could be a topic, with the miles on this engine...but I have not got means to do a rebuild, and that's the way the cookie crumbles, as they say.....
Jota...these valves you mentioned appear to be the valves that are fitted on the large diaphram that uses vacuum to assist the brakes on older this correct?
Thanks once again....ALL OF YOU.....I will drop a note when I have more info to plague you all with....thanks!
The breather valve used from the case to the tank is for a brake booster. I will try to get you a number / manufacture name that will work for you over there. Worst case scenario i can mail you one. As far as wet sumping goes, i have a 850 MKIII that had all the mods done to it during manufacturing. It still wet sumped no matter how many times i rebuilt the pump. This year i installed a one way valve and my troubles are gone . I did install a pressure gauge ( $30 Cdn )also, not so much because of the valve being installed but more because i needed something to keep me occupied. I had concerns to about the valve but i think you will find that Colorado Norton Works puts them in all their bikes and according to Matt Rambough they have never had any troubles nor could he take the risk of having a oil problem. That was certainly good enough for me . If you want to send me an e-mail address i will send you a few photos of the valves installed and my oil pressure gauge . Not much on posting pictures on this site otherwise i would . Sorry !!
Thanks Ron....

Thanks for the offer of help....downright kind of you!

Would like to see the pics...look for PM.

Did a stop at the parts store today though, ....the poor clerk had to go to the boss and ask what to do with my request. Turns out, the valves are only available from auto dealerships here. Did the thing at the junkyard instead, and got a couple from cars, one with a smaller inside diamiter than the other. Picked the bigger of the two....from a VW I think and have put it into the tube already. Will have to wait and see what it does, still have the oil drained and the primary open to clean the clutch, and still not sure if I have the needed stuff to do the oil pump repair....anyway, the valve is in and we will see soon what it does....bit nervous about it, as I have had such good luck with the dear lady and just as most of us know, changes can result not only in a ladies' pleasure, but also in her displeasure....... :wink:
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