OIl leak and mysteries of BSA A10 oil system

[boltzmann]

Hello fellas,
Let me start off by saying that I am unclear on the fundamentals of oil delivery on our bikes. Although I have read some threads elsewhere on wet-sumping and various modifications such as check valves etc. that can be installed, I still do not understand the basics of how the BSA pre-unit oil system works.

My A10 has oil that "appears" on the top fin. Since I bought it I have not ridden it much because there are a couple items that need to be ironed out before she's road worthy, so after it sits for a day or so, this oil appears. The couple of times that I have rode it, I noticed some oil leakage around the rocker box covers, etc. but after cleaning all that up oil still accumulates on the edge of the top few fins.


Following advice elsewhere on this thread, I removed the oil tank for the first oil change in order to flush it. It does have some sludge in the bottom, although it's not too bad. But further adding to my confusion is the "crimped" oil line inside the tank. Is this by design? if it is, what is the purpose of the hose attached to it (that goes to the crankcase which I assumed to be a return)? Any information would be much appreciated.

[Triton Thrasher]

Looks like a rocker cover to head joint not sealed, or leaking rocker oil feed pipe union.

Are the screws tight?

The return pipe from the sump is crimped flat and a hole is drilled into the side of it, I think. Forcing the oil through a small hole is thought to burst air bubbles and reduce frothing in the tank.

The hole also slightly restricts the return, forcing some oil up the pipe to the rockers.

[A10Boy]

There are plenty of drawings, sketches and explanations on the internet regarding the a10 oil system. However, this looks like a basic leak not a problem with delivery.

[boltzmann]

Great thanks TT, I wondered if the crimped pipe didn't provide some back  pressure. I was thinking of redoing the rocker cover gaskets anyway.
Here's another question: Is the oil feed pipe chrome plated? This one is. The previous owner chrome plated all kinds of things. I'm thinking it should be brass and I don't know if the chrome  would affect it's ability to seal properly.

[morris]

Most have the odd weep but that does seem to be a lot of oil coming out.
There should be a fibre washer between the rocker box and the union. Between the union and the bolt its a taper that seals it up, but if the taper is damaged or not the same angle on both bolt and union it will not seal properly.
The right hand side is sealed by a copper washer.
All of the oil feed pipes I came across are chromed.

[East_Coast_BSA]

My oil feed is Cad-plated.  My new fiber washers became very loose in short order, as they compressed after a few heat cycles.  If you had installed new washers, it's almost guaranteed that the bolts are now loose.  The thick paper gaskets on the rocker-box base will do the same thing.  You should re-check the tightness after a few heat cycles as those gaskets also compress.

[boltzmann]

Great thanks for the tips!
Yesterday I had a little time to remove the rocker box. It had had new gaskets put on very recently, like I would say under 100 miles. The work looked a little sloppy, as in way to much gasket sealer all over. Im going to cut out some new gaskets and re do it. Ill pay attention to the fiber washers on the oil feed as well.
Guess Ill get some practice aligning the pushrods when I seal it back up.
Also will check cylinder head bolts for proper torque while Im in there.

[Viking]

It is often the rocker box that is seeping oil.

Why does it do that?

The cylinder head has a uneven gasket surface. From being dismasted many times the last  60 years. Heated to remove valve guides etc.

Cure: Make a plane/tool to fit the cylinder head in a milling machine, and mill the gasket surface true..


The Rocker box has an uneven gasket surface. From being dismasted many times the last  60 years.

Cure: Get the rocker box machined to have a true gasket surface.

It works: I have done it on several A10 engines. And they are oil proof after the treatment.