Multiple oil puddles on ground after short ride

I’ve got a ’70 Commando that I have been chasing oil leaks for quite some time now. After sitting for half an hour following a 25-mile ride, there will be 8 - 10 square inches of fresh oil, directly under multiple spots throughout the engine and gearbox. I am no stranger to British bikes and their tendency to leak, but I believe this is beyond the “normal” puddling. I had the notorious ’71 oil-in-frame Bonneville for 12 years, and it never dripped like this.

This bike was completely overhauled and restored by the previous owner a few years back, prior to my purchase, and he is very knowledgeable on vintage motorcycles in general and Nortons in particular. I'd like to think that the main case seals for both the engine and the gearbox are good, though perhaps this is wishful thinking. It likely sat some after the restoration, for what that is worth.

Over the course of my ownership, I have made the following repairs and modifications. Most were ideas I picked up from similar threads on this forum:

• Dry primary with belt drive from CNW. New primary cover O-ring gasket.
• PCV conversion from JS Motorsport using the drain plug reed valve and plugging the OEM disc valve outlet
• Plugged the chain lube drip tube
• Replaced (seeping) rocker box gaskets; now dry
• Replaced (leaking) kickstart O-ring and shifter shaft seal; now dry
• Replaced (leaking) tach drive base gasket; now dry
• Pulled oil tank, cleaned it completely, and let it sit overnight filled with fluid covering all connections and fittings. It was completely dry externally the following morning. I found no evidence of a static fluid leak on the bench. Saw no seepage when I pressurized it a bit with compressed air. I did hear it “oil can” a bit when I did this. I saw no evidence of damage, however.
• Cleaned engine externally as best as possible to remove as much residual oil as I could.
• Used compressed air to verify all ports in and out of the oil tank were clear.
• Drained the engine of oil as best I could. I kicked it over repeatedly to get oil to come out the return hose to the tank.
• Replaced the tank and filled it with exactly two quarts of oil (my bike has no oil filter) in an attempt to minimize blow-by.
• Ran the vent tube that originally went from the OEM disc PCV valve to the oil tank and ran it from the oil tank into a catch bottle to verify minimal or no tank pressurization on the road. The bottle is basically dry inside after about 50 miles.

Oil is dripping from various points all around the underside of the engine. The plate under the oil tank and battery (that I cleaned quite well) continues to collect oil. It drips and blows all over the gearbox, swingarm, back half of the engine cases, rear fender. Oil also drips from the bottom of the front half of the engine, too. There is oil dripping from the lower mating surface of the crankcase to the “dry” primary cover. Basically, the entire underside of the engine is either wet or dripping after 20 miles. There is even fresh oil on top of the back half of the primary case. The bottom pleats of the air filter are a little damp from oil, though perhaps this is normal (?) considering the location of the PCV vent into the carbs. The hoses from the tank to the engine case and the fittings at the tank are dry. The fitting on the engine case is moist, but this may be from oil coming from a different source.

My current theory is that the oil tank is leaking in a manner that would not show in a static bench test, even though (as far as I can tell) the tank itself is not overly pressurized during operation. This seems like the only way oil would collect under the tank and battery (?) But I am open to any suggestions as to what to do next, what I may have overlooked, or what I may have done incorrectly. I am hoping that this doesn't require major surgery to the engine or gearbox cases, but I'll do what it takes.

Again, I don’t expect a leak-free, vintage British twin. But just a few drops on the ground would be nice.

Dont know about the 70 oil tank but the later oil tank's bottom threaded support insert cracks around the edge creating a leak. Cure is to weld a plate over the insert and allow the tank to rest on the bottom support, top mounts are strengthened too.

According to the Andover Norton parts listing the interim 70 had the later oil tank that gets the bottom leak.

Sounds like you’ve done some good work to the bike and honestly, it should be (almost) leak free.

All I can advise is this: remember that oil spreads well and always obeys gravity. In other words it’s unlikely you have multiple leaks, but rather one generous leak.

Clean scrupulously then take on a short run and inspect all possible points very closely. Repeat this and you should see some evidence of the source.

Fast Eddie said:

always obeys gravity

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Except at speed, odd things happen in the airflow with oil going upwards and even forwards.

kommando said:

Except at speed, odd things happen in the airflow with oil going upwards and even forwards.

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Absolutely.
But then when parked, it’s all gonna drip down, and make it look like it’s coming from everywhere !

Plus the bottom insert of the oil tank, when it cracks, can sometimes only leak when the engine is running and the vibration opens up the crack.

PDE 70 Commando said:

I don’t expect a leak-free, vintage British twin.

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You should.

I'm guessing yours is the 'Hamcan' oil tank which forms the rear face of the air filter box?
The tank vent is an internal pipe which exits into the airbox, so it's just a hole in the front face of the oil tank. Have you checked if this is venting oil?
If this internal pipe has fractured it would dump oil into the airbox, and then everywhere else.
Later side-mounted tanks have an external pipe which plugs into the back of the airbox, so it's easy to check.
My '70 had a frustrating oil leak which turned out to be the triangular plate at the back of the timing case - a sliver of the thread broke away and wedged itself between the case and the plate; it took some finding
Happy to report it's now oiltight, so they're not leaky by design - as @ludwig says.
Incidentally, I removed the timed breather disc and plugged the pipe into a cheap PCV close to the tank, which worked well enough for a stock motor.

Invest in a gallon of brake cleaner and a pressure bottle.
the cleaner is cheap when bought in bulk, and way more effective than the old Gunk & Jizer we knew and loved (but not the stink).
It washes the oil off instantly and leaves a dry surface, so tracing the leak source is a LOT easier

Keep at it until you find the leak
A commando really shouldn't be leaking oil at all
A UV torch can help especially when it's clean fresh oil
Degrease everything and start the engine in the dark
A UV torch will pick it up way quicker than the naked eye in daylight

When I fitted my reed valve to my sump I had oil every where all over back tyre drips everywhere. Long story short , I put an o ring on my oil tank filler cap as well as cork washer , I have to do it up with a wrench but no more oil . Worth trying sorted mine right out .

PDE,
When you remove the outer primary cover,is there oil (excess) inside.With the belt it should be fairly dry. If not you will need a new main seal.Are you also losing trans fluid?As Ludwig says, you don’t need any leaks.Good luck with your findings.
Mike

Caution! Brake cleaner can remove paint! Spray Gunk, the original, and wash off with hose carefully.
My MKIII did crack the oil tank around the bottom stud and I simply mig welded the crack. Maybe it'll crack again but it's held for years but not too much use.

JimNH said:

Caution! Brake cleaner can remove paint! Spray Gunk, the original, and wash off with hose carefully.
My MKIII did crack the oil tank around the bottom stud and I simply mig welded the crack. Maybe it'll crack again but it's held for years but not too much use.

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I've never seen brake cleaner remove paint otherwise it wouldn't be fit for purpose. Maybe different formula in the US?
I've been using it for years with zero issues. Kerosene would be an option i guess, as this is what I have in my parts washer.

Are all the engine mount fittings and crankcase fittings tight?

kommando said:

Dont know about the 70 oil tank but the later oil tank's bottom threaded support insert cracks around the edge creating a leak. Cure is to weld a plate over the insert and allow the tank to rest on the bottom support, top mounts are strengthened too.

According to the Andover Norton parts listing the interim 70 had the later oil tank that gets the bottom leak.

Andover Norton Parts Drawings - Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

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I can confirm that my bike has the earlier "ham can" or "top hat" tank. I have heard that this tank is far less prone to cracks and leakage than is the later version. That is NOT to say that it cannot crack and leak, of course!

Fast Eddie said:

Absolutely.
But then when parked, it’s all gonna drip down, and make it look like it’s coming from everywhere !

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Exactly! And the fact that I even see a few drops of nice, clean oil on TOP of the rear half of the primary keeps pulling me towards the oil tank that doesn't leak -- on the bench, anyway!

BERT said:

Are all the engine mount fittings and crankcase fittings tight?

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Yes, they seem to be.

Where does the reed valve vent to?

YING said:

PDE,
When you remove the outer primary cover,is there oil (excess) inside.With the belt it should be fairly dry. If not you will need a new main seal.Are you also losing trans fluid?As Ludwig says, you don’t need any leaks.Good luck with your findings.
Mike

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It was leaking trans fluid from the kickstart O-ring, but that has been resolved. Of course, it now has a new outer gearbox cover gasket, too. As for leaks further into the gearbox, I am not sure at this point. More cleaning, short rides, and UV diagnosis is in my future for sure.