Oil Tank vent leak

Hi ,
I'm new to this forum and have had my 1969 Commando 750 Roadster for about 9 months.
I've only had it on the road for about 3 weeks as I spent time rewiring it and tidying it up a bit.
It runs a treat but leaks oil out of the tank vent where the air filter sits.It's got the same oil tank as as the S model. It has a couple of small splits in the front plate above the vent outlet and a bit of oil is seeping out here but I'm getting a lot of oil out of the vent its' self .
I looked at other threads on here and gather this is a common problem.Has anyone tried putting a new vent outlet in the top of the tank and blocking up the factory outlet so the air cleaner doesn't turn into a soggy oily mess? ! Could then run a hose from the new vent into a can.
I'm mystified how the oil gets into the top of the vent pipe which is well above the oil level in the tank.
I'm now running my oil level very low and this has reduced the mess coming out of the vent but not stopped it completely.

I did try disconnecting the crankcase breather from the tank and running it into a can. That stopped the mess out of the vent pipe but too much oil came out of the breather to run like this for very long as it filled up the can and the oil level in the main tank dropped. Obviously the breather needs to discharge into the oil tank so the oil goes back in there.
Anyone else had this and managed to come up with a solution?
Any advice much appreciated
Regards
Phil

Yes, that is a problem. I put a little aluminium tray under the airfilter to keep the oil off the wires. I'm thinking about adding some of that oil absorbing mat to the tray. One sized for a car should be a year's supply. The famous Norton Oil Bath does keep the back of the bike from getting rusty.

Greg

My 69 is not back on the road yet, but coming. I always had that problem with that hole in the air filter box leaking and getting all over the gearbox. I am thinking about drilling a hole in the chromed air filter cover, threading or JB welding a small pipe fitting in that hole and running a plastic hose out of the front of the airbox and down to the side of the bike so it just doesn't keep oiling the rear wheel, or you could put it into a collector and empty it every ride. That tophat breather thing really shouldn't be leaking much oil, but it does. Only other good option is to block off the timed breather and put a real breather in the magneto position and drill some extra holes in the timing side case, which involves breaking the cases apart. Still need to let the oil tank breathe, but at least it may not be pumping that oil from the crank.

Dave
69S

Dave,
Thanks for that. I saw your reply to me on the British Bike forum as well.I agree that the real solution must be a better breather using the timing side. My bike has a plate bolted across where the old points unit or mag used to sit. I've seen the other threads on here about this conversion using reed valves etc. and that looks good except that's beyond me, I'd have to get a pro to make and machine all the parts.I'm determined to use the bike for the rest of this year so don't want to get into major work like that at present.
Your S model looks good.
Regards
Phil

philterman said:

My bike has a plate bolted across where the old points unit or mag used to sit.

Click to expand...

The blanking plate in the "old magneto position" covered the opening meant for an electric starter which the factory never fitted. No Commando had a magneto as standard, and the 20M3S models didn't have any machined opening for the 20M3 points housing, only the starter drive blanking plate from serial number 133618 (or 136618).

My 'S' is a solid casting in the magneto area. Its like they decided just to block it off and forget it.



Dave
69S

DogT said:

My 'S' is a solid casting in the magneto area. Its like they decided just to block it off and forget it.

Click to expand...

As it's an S, then it ought to be a pre-"starter motor" 20M3S case, presumably with a serial number lower than 133618 (or136618)?

The blanking plate arrangement continued on from 133618/136618 (approx. prod. date April '70) until late 1972 when the factory went back to a "solid" case again.
http://atlanticgreen.com/engcases.htm

Yes, 132031.

Dave
69S

What an excelent site this is. Very friendly and the multitude of topics really help norton first timers like me. Re the blanking off plate. I also have a 'S' type of 1970 vintage with solid casting. Also found that oil migrated from breather into the air filter but noticed this was greatly reduced if the oil level is kept half way between the low and high marks on the dip stick.

Always a pleasure to help, we all need it at one time or another.

Dave
69S

Dave,
Took your advice and took the elbow off to expose the timed breather and it appears to be working fine. This all tends to support what everyone else has been saying, i.e. "they all weep oil out of the oil tank vent."
I'll just have to put up with it for now until rebuild time.
Regards
Phil

Phil,

Al on the britbike forum seemed to have luck with his. I looked at the Norvil site as he suggested and the Oil Breather page. I think Les is referencing a 71 and up oil tank. On those tanks, you can get lines mixed up. My dip stick is about 4 1/2" long the high mark is at 3" and the low mark at 4". Probably a good idea like Les says to use only 50 W oil and maybe keep it on the low side. It may help. I should be getting mine running in a month or so and I'll see what happens with all the new seals and Hylomar gasket sealant. I do have a bit of oil in the sump now and it is not leaking out the crank flanges. Good sign.

Dave
69S

So far, much suspicion has been levelled at the engine breather being the possible cause of the tank breather leakage, but what about the scavenge oil?

Could the scavenge return pipe arrangement inside the tank actually be causing, or at least contributing to the tank breather overflow problems?

I have always thought the problem is in that area above the main tank, in that little tophat thingie that I think Les is referring to as the "froth tower". Not sure. However, the 69/70 timed breather goes into the side of that tower and the vent line from the airbox goes up there too, more or less in the center of it. If frothy oil is coming in the side, there may be some oil or vapor that manages to get into the vent line. I wish I could see exactly what is up there. I wonder if the tower is soldered on or brazed on, it may be worth a try to take it off and see what is going on in there and the pipes may be able to be re-arranged so the engine breather oil can't get into the oil tank vent. If we could put an upside down "P" trap on the vent it may stop it.

I just looked in my tank with a bright light in it and the vent line goes up right along side the front of the tower, can't see how far, it may be attached, and the side tube just goes into the side and ends.

It's brazed on, I just scraped the paint off, do I dare take the oxy/acetylene to it?

Dave
69S

Dave,
The breather line on mine goes into a pipe stub that is brazed/welded to the tank top right next to the top hat thingey.It doesn't actually go into the top hat. I think it just ends inside the oil tank next to the top hat.
Is yours the same?
I'd be really interested to see just what the arrangement is inside the tank/top hat. I think these tanks are very rare now as Norvils don't list them. If you're really brave cut the top off but I'd be worried in case of damage as a spare's not going to be an easy find.
Phil

Here's a picture of the top part of my tank, the front is to the left. I'm prepping for paint. My breather line goes right on that stub and that stub ends just on the inside of the top hat. My vent line from the front of the tank in the airbox goes up into that top hat at the front of it, I can't see how far by looking into the tank. I'm tempted to hacksaw off the very top of that top hat, and maybe put an elbow on the stub inside so it can't splash into the vent tube top if that is what it is doing. Other thing that could be done is to put a trap on the top of the vent that bends straight down, just enough to keep things from falling right into the top of it if it indeed it just stops straight up. It would be easy enough to solder or braze the cut off part back on and fix it to look like new.

What is your engine/frame #? Mine is 132031, Apr. 1969.



Dave
69S

Thats interesting my 1970 oil tank is slightly different, may be a slight upgrade?

Interesting. There must have been 2 (or more) oil tank versions for the early 69/70 models. What is the number on your frame possm? Looks like yours is like Phil's, the way he describes it.

Dave
69S

Yep, my tank's exactly like possm's.Not sure of the exact year of my frame as it's got a French type approval plate on the headstock in place of the Norton ID plate and the frame number listed on it is one digit short .It's 13047.The engine number is 20m3s155478 which is much later but still has the blanking plate where the Mag on an Atlas would go.
My first Commando was a 1969 S model and it also had the same oil tank as the one I've got now, like possm's .
I think the breather inlet pipe stub might just poke down a bit into the tank and if that's so, how does oil which comes out of the breather pipe and is directed down into the tank get all the way up to the top of that tower/hat thingey and then into the vent pipe?
If I could get hold of a spare tank I would cut the top off just to see what's going on inside.
Possm, does your tank leak out of the vent?
Phil

the bike i am building came to me in pieces and 75-80% complete i have never had it running as yet ,it is matching # and late 1970 manufactured, It actually came with two 0il tanks and the spare one is fitted with a vent fitting out of the raised piece, in blowing compressed air into the pipe showen in my earlier photo air deffenately entered and exited the oil tank before exiting via the aircleaner vent.
Al