Central oil tank leak

freefly103 · May 21, 2023

Have been chasing a leak for a while, am now suspecting its coming from the centrally mounted oil tank.

Has anyone removed a centrally mounted oil tank before with the engine in the frame?

Saw this post:

1969 / 1970 S type oil tank.

Hi All. I have two type of oil tank with different oil breather tubes on the top. One has two breather tubes, one to connect the engine breather and one that goes free in the air; there is a hole on the air filter mount that remain close in the air filter system. The other is the same but...

www.accessnorton.com

Can anyone confirm that the red line shown leads to a breather hole?

L.A.B. · May 21, 2023

freefly103 said:
Can anyone confirm that the red line shown leads to a breather hole?

Yes.

gjr · May 21, 2023

Where are you seeing the evidence of the leak ?

The breather will drool oil on to the bottom of the air filter and from there on to your alternator wires and gearbox.

freefly103 · May 21, 2023

gjr said:
Where are you seeing the evidence of the leak ?

The breather will drool oil on to the bottom of the air filter and from there on to your alternator wires and gearbox.

Yes, that exactly what’s going on.

The hole doesn’t seem to be tapped with any thread. Was thinking to connect a tube to a catch can to collect the oil.

If any one has done this, would appreciate your suggestions.

marshg246 · May 21, 2023

gjr said:
Where are you seeing the evidence of the leak ?

The breather will drool oil on to the bottom of the air filter and from there on to your alternator wires and gearbox.

There are two types of center tank. 1) Engine breather connects to froth tower 2) Engine breather connects to a pipe in the top of the tank.

For type one, the breather points directly at the end of the pipe that goes to the bottom of the air cleaner. If you add a sump breather to the engine, lots of oil is shot at the end of the pipe to the air cleaner and out the bottom. If you have the standard timed breather, then only air and vapor is in the breather line and there should be no (or extremally little) oil getting into the air cleaner.

Type two completely eliminates the problem. I built a 69S with a cNw breather and it took a while to understand that leak. Only did when I put a camer in the froth tower. I found a type two oil tank on eBay and replaced the type one that was on the bike.

The engine does not have to come out.

freefly103 · May 27, 2023

The vent pipe is approx 7mm in diameter. Since I didn't know how thick that pipe is, I tapped it to M8 to allow sufficient thread engagement but not go through the pipe and into the oil reserviour.

Then off to the plumbing store I went for some fittings.

My machinist and fellow Vintage Bike enthusiast (1956 BSA), machined the head of an M8 bolt to fit the BSP threaded elbow and also drilled through it to allow air to flow from the oil tank breather pipe to the breather tube and utlimately to the catch can / filter.

The other end of the elbow is a 10mm spigot for the breather tube.

I fitted the M8 end of the elbow to the oil tank breather pipe and the other end to 10mm pipe and breather catch can / filter.

The catch can / filter is located under the seat above the rear fender.

I'll see how it goes and maybe come up with a better looking solution in the future, as the result looks like the bike crashed into the plumbing supplies shop where I bought the fittings from.

Both the 70 and 72 bikes now have the same mod. Pics are for the red 70 bike.

TBW · May 27, 2023

freefly103 said:
The vent pipe is approx 7mm in diameter. Since I didn't know how thick that pipe is, I tapped it to M8 to allow sufficient thread engagement but not go through the pipe and into the oil reserviour.

Then off to the plumbing store I went for some fittings.

My machinist and fellow Vintage Bike enthusiast (1956 BSA), George (in the pic), machined the head of an M8 bolt to fit the BSP threaded elbow and also drilled through it to allow air to flow from the oil tank breather pipe to the breather tube and utlimately to the catch can / filter.

The other end of the elbow is a 10mm spigot for the breather tube.

I fitted the M8 end of the elbow to the oil tank breather pipe and the other end to 10mm pipe and breather catch can / filter.

The catch can / filter is located under the seat above the rear fender.

I'll see how it goes and maybe come up with a better looking solution in the future, as the result looks like the bike crashed into the plumbing supplies shop where I bought the fittings from.

Both the 70 and 72 bikes now have the same mod. Pics are for the red 70 bike.

Good stuff. It‘s probably just the photo but are you missing a nut from your L/H Z plate ? Top rear…

freefly103 · May 27, 2023

TBW said:
Good stuff. It‘s probably just the photo but are you missing a nut from your L/H Z plate ? Top rear…

No, it’s just the photo

freefly103 · May 28, 2023

marshg246 said:
There are two types of center tank. 1) Engine breather connects to froth tower 2) Engine breather connects to a pipe in the top of the tank.

For type one, the breather points directly at the end of the pipe that goes to the bottom of the air cleaner. If you add a sump breather to the engine, lots of oil is shot at the end of the pipe to the air cleaner and out the bottom. If you have the standard timed breather, then only air and vapor is in the breather line and there should be no (or extremally little) oil getting into the air cleaner.

Type two completely eliminates the problem. I built a 69S with a cNw breather and it took a while to understand that leak. Only did when I put a camer in the froth tower. I found a type two oil tank on eBay and replaced the type one that was on the bike.

The engine does not have to come out.

freefly103 · May 28, 2023

Could you post a pic of the type two oil tank? That would be helpful.

B+Bogus · May 29, 2023

Here you go...

freefly103 · May 30, 2023

B+Bogus, thanks for sharing. I have the second type shown in your pics above.

I think there are multiple leaks going on with the bike. After the first ride since installing the breather, the bike still leaked from that breather hole. I checked the oil tank level. I had filled the oil tank as usual so that the dipstick showed half way between the bottom and top indicator lines. It seems this was too much oil and the leak persisted. I extracted about half a liter so that the oil level was just touching the end of the dipstick. This alleviated most of the issue.

Now I have a small oil leak which looks like its coming from one of the bolts that secure the oil tank to the tray that connects it to the frame, another one (dark oil) from the inner primary and another most baffling leak of clear oil that appears on the crankcase behind the barrels. Can only be gear oil? I recently just changed the gear oil so will look into that but how does gear oil get on to the cases behind the barrels?

I'm struggling a bit here but it seems that I should at least pull apart the primary including the inner primary to check the seals and have a good look at the gear box to see if any any oil is coming from there.
Or just leave it since the leaks aren't that bad. Seems like every time you sort one leak out, there's another two that become apparent.

marshg246 · Jun 3, 2023

freefly103 said:
B+Bogus, thanks for sharing. I have the second type shown in your pics above.

I think there are multiple leaks going on with the bike. After the first ride since installing the breather, the bike still leaked from that breather hole. I checked the oil tank level. I had filled the oil tank as usual so that the dipstick showed half way between the bottom and top indicator lines. It seems this was too much oil and the leak persisted. I extracted about half a liter so that the oil level was just touching the end of the dipstick. This alleviated most of the issue.

Since you have the tank where the breather goes in the top rather than the froth tower, you need to get a camera and look at the tube to the air cleaner. The open end of it is in the froth tower well above even an over filled oil tank. Your tube may have a hole in it! When not running, even if you filled the tank well above the high mark, no oil should come out of the tube in the air cleaner.

Central oil tank leak

freefly103

1969 / 1970 S type oil tank.

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