BSA Gold Star oil return

[bigjos]

Hi, I have just finished rebuilding a DB32 350cc Gold Star. It started fine and ran for a few minutes then stopped. When I tried to kick start it I could not turn it over. Left it for little while and squirted oil in bore and its freed up again now.
On investigation I cannot see any oil returning from the oil pump - since the return pipe also feeds the oil to the rocker box I am thinking this is the problem.
I have taken the pessure release valve off and confirm oil is being pumped that far. Also took timing cover off and pretty sure oil is getting to the crank and cam shaft feeds (difficult to be certain!)
So having read other topics on this page I wonder if I just need to fill the sump up so that there is oil there to be pumped?
I have poured about a 150 ml into the crankcase but still no sign of anything coming out of the return.

The other thought is that feed and return pipes might be transposed - but if this was the case would I still see oil out of pressure relief port!? Anyone know which is supposed to be which (I have the outer pipe connected as the feed and the inner as return?)

[chaterlea25]

Hi Bigjos,
The crankcase should be marked which is return, the outside one

A problem with all BSA pre unit singles is that the oil pumps can and do tighten up (seize) when bolted back into the engines, The casualty of the pump tightening up is the worm drive which will strip the teeth
Make sure the pump and its drive parts are OK before going any further
The pump may appear free when not fitted but tighten up when bolted in place
Fit a pair of 1/4 x 20 nuts to the pump fixing bolts and tighten them to simulate the pump being fitted to the engine
and make sure it turns easily

Did you prime the engine oil ways and oil pipes before you started the engine? This is important to do
Was the engine standing for a long time before you went to start it?

John

[iansoady]

If you have the pipes disconnected, put your finger over the end of one and turn the engine over smartly. If you feel suction, it's the feed; if it blows your finger off it's return. If neither, there's an oil pump problem.....

[Rex]

Don't think you'd get noticeable "suction" or pressure with a BSA geared oil pump pumping air at kick-over speed, but my guess is as above, that old BSA Mazak oil pump body tightening syndrome.
They tighten up even when they're not being used, so my thoughts would also be to take it out for inspection.

[bigjos]

Yep - looks like Ive got the pipes connected the wrong way round!

Can just make out the marking on the outside of the crank saying "return" and like a numpty I've connected the feed there! Will swap them over tomorrow and try again.

Watch this space!

Thanks for all the help

Ian

[Rex]

And just when I thought nothing would surprise me any more in the world of old motorbikes...

[33d6]

Thank you for replying and being honest BigJos. We rarely get to know the result of our discussions. It's uncommon in the queries here for someone to come straight out and say 'Whoops, I made a mistake'. It takes a man to do so.
Cheers,

[john.k]

Fortunately a roller bearing single will run for a long time without damage if there is a dollop of oil in the cases to begin with.

[iansoady]

It would be the piston I'd be concerned about especially as it was mentioned that it had seized, however lightly. I agree that rollers and balls require little in the way of lubrication.

If it was mine I would be popping the head & barrel off to check.

[bigjos]

Everything is moving freely now and engine start and runs sweetly! It’s a new piston in a rebored cyclinder so was probably a close fit anyway.
Thanks for all the advice.

[iansoady]

A couple of years ago I had a 1931 Sunbeam 350 which would tighten up if worked hard, freeing off when left for a while. At first I thought it was an oiling problem but eventually realised that the barrel / piston clearance was inadequate - it had been rebored by a previous owner, and apparently had been returned to the supplying dealer as it had seized.

I had a couple of thou honed off by an old school engine reconditioner and it was fine. I always go for generous clearances ("racing" clearances as we used to call them) as I'd rather have a little bit of piston slap than worry about it tightening up. If you look at the wear limits quoted for many of our old bikes, they are quite large - eg .008" bore wear for my Norton ES2 is the recommended maximum. This is enormous compared to what modern engines will put up with.