BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: Caulky on 17 April, 2017, 13:31:49

Title: Oil pump
Post by: Caulky on 17 April, 2017, 13:31:49
1971 A65L
I bought a new spindle for this pump because the old one had chipped and worn teeth.
After disassembling and cleaning, I find its a little tight to turn.
Maybe it will be ok after its 'run-in'.
It will turn using a screwdriver, but not using my fingers.
Is this normal or should I take it apart again?
Title: Re: Oil pump
Post by: JulianS on 17 April, 2017, 13:59:00
I presume it is a cast iron pump rather than the zinc alloy one (if its zinc alloy they are often found to be distorted)

There will be some drag when you turn the pump with thumb on worm on the driving spindle caused by the gears and the O ring, but with the spindle housing off it should turn with your thumb.

Sometime loosening the assembly screws allow it to turn freely indicating something is too tight inside.

There may be damage to the housing caused by the chipped teeth or spindle is too tight in the housing, either by diameter or by lack of lateral movement - the thrust washer which fits over the end may be too thick to allow your new spindle to rotate freely. You need a little end float.
Title: Re: Oil pump
Post by: Caulky on 17 April, 2017, 14:30:40
Thanks for the reply Julian.
Its a zinc type..
There is a little spindle 'end-play'.
Turning by screwdriver a few times, (with the oilways full of oil there appears to be a slight 'high spot' at a certain point.
Oil gets pushed out of the top holes, I presume the lower ones suck, because the oil disappears.
Maybe I'll remove the four base screws and try turning again.
Other than that, I could use a drill to give it a bit of run-in? 
Title: Re: Oil pump
Post by: JulianS on 17 April, 2017, 14:45:49
The zinc bodies distort mainly due to pressure from the three mounting points. The oil chambers, the screw holes and  the spindle housing can get squashed a bit causing tightness. Many pumps work quite happily with this but the possibilty is reduced pressure.

You may be able to see a witness mark where it is tight inside but you need to be careful what you do  incase you cause a lose of pressure.

If the steel end cover is scored you can flatten it by lapping on a surface plate. I advise against lapping the body or cover to the body, or the spindle housing or spindle housing to the body because it will reduce lateral clearance of the gears and may make the pump even tighter.

I have not used an electric drill to "run in" an oil pump.
Title: Re: Oil pump
Post by: Caulky on 17 April, 2017, 15:16:22
Thanks again for your advice.
I really can't remove the spindle again.
Medical conditions make certain tasks difficult, I had to take the pump to a mate in a garage to remove the circlip, which even he struggled with.
I wasn't trying to be a cowboy WRT the turning by drill, it just occured to me that if it goes back in its present state, that is what will happen.
As you appeared to be saying, a little tightness could be alright, but any body lapping is out of the question, I think it will be assembled "as is".
Its going to have an oil pressure gauge on completion, so I can monitor the pump efficiency then.