650ss oil leak from tank

I had a similar problem and found it was the lip that the cap twists onto. It seems to only be soldered on and the solder had cracked. Silver solder and powder coating sorted mine out.

The oil level doesn't have to be anywhere near the top of the tank to still get leaks from the oil tank cap. When on the road, the oil slops about considerably inside the tank and will reach the oil cap on the slightest of bumps or hollows.

So the leak has to be either the cap seal or the joint around the top of the neck. I got away with turning the rubber seal that's inside the cap up-side down to cure my leak, but you could also check for flatness across the top of the neck with a small block of flat wood (or something similar) and ultimately, do a pressure test with a bicycle/airbed pump and a bowl of water.

Also, is the oil tank breather free? Put a piece of clean rubber hose onto the breather and blow into it to see if it is actually able to breathe.

Oil tanks can crack where the top bracket attaches to the tank. Worth a careful check there.

Previously david_metcalf wrote:

Previously terence_rafter wrote:

I had a similar problem and found it was the lip that the cap twists onto. It seems to only be soldered on and the solder had cracked. Silver solder and powder coating sorted mine out.

Is the solder around the base of the lip ?

"Neck" is probably a better description. At it's base, where it's joined to the tank, is where mine leaked.

I have recently restored a 1967 650ss and have only just got it running. I have found that after a few miles when the engine is warm, there is a steady trickle of oil coming out of the oil tank cap. Obviously first thoughts were too much oil in the tank but this is not the case. The breather from the crank case is clear and to the chain guard is clear. I have checked the oil immediately after a run andit is quite frothy (not sure if this is normal) but is nowhere near the top of the tank. I have changed the oil tank cap but has made no difference. Any suggestions would be greatly appreciated.

I had this problem on an Atlas motor in an N15CS. Blew oil out of the oil cap hole at speed. I disconnected the engine breather from the oil tank & led it via a longer& wider pipe to the rear end & open air. I assume the breather was pressurising the oil tank, as has already been suggested. TTFN Jack