The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Else on 23.03. 2026 09:37
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Hello all. I would like to test my oil pump to make sure it's pumping the correct amount of oil and can maintain decent pressure. I get return to tank but not much, just intermittent spits of oil. Doesn't look enough to me. I have stripped it and checked for wear, looks very good so I suspect it has been replaced recently. It has an SRM pressure release valve fitted which I have also stripped and cleaned and inspected.
Does anyone know who could test it for me?
Thanks Andy
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if it's not chucking oil out of the breather all over the floor when the bike is running it is working ok, they all spit oil with air it means they are doing their job.
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Plenty on the forum about the oil pump. Whenever I build a pump a quick test for freedom of movement as each gear is added is to drive the input gear with a rod with a cut out at the end to engage the driven tab. That way each gear can be added and if things tighten up repositioning the gear teeth makes it move smoothly again. Reckon this is why it was recommended to keep the original gears in exactly the same relationship to keep the wear patterns matched on the gear teeth. Not so building a pump from the best of the bits.
Once the pump body with gears is assembled, nose and base plate added and tightened down and everything is turning smoothly with no tight spots, use the rod in a cordless drill to drive the pump with the inlet and scavenge ports immersed in oil.
A good pump will give a jet of oil from each outlet port. I used a ball point pen as a drive rod, nothing special. Once satisfied with the gears and pump performance, add the drive spindle and test that the pump can be turned by hand. These spindles can also go tight, if so reposition by half a turn. If there is no improvement try another if you have one...or relieve one side of the slot to give a little leeway on the driven tab. Add the retaining ring only when the pump is the best it can be.....the old Mazak groove for the ring is easily damaged. .
As Berg's says, they will gulp and spurt oil when the sump is getting empty. That's the scavenge function working. More oil in the sump gives a constant stream.
Swarfy.
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Else, The scavenge/return side of the pump has larger gears, and pumps about 30% higher flow rate. So intermittent air bubbles is quite normal.
Col
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Apologies for my previous post where I got completely muddled with tech terms. Here's what I should have said.....
Interesting...... A mate of mine had poor return to the tank. To cut a long story short, we ended up removing the SRM anti wet sump valve, problem solved! It seemed that the SRM anti wet sump valve was preventing some of the oil getting into the gallery prior to hitting the timing side bush. I suspect the spring was getting coil bound before the ball had cleared the oil gallery. The bike had seized on three occasions prior. Having removed the anti wet sump valve, we ran the bike with no ball and spring (AWS) for a while and the oil flow back to the tank was excellent. We then fitted an outboard Anti wet sump valve (I know, not everybody likes or approves of them) and this prevented wet sumping and did not affect the oil return to the tank. More recently, a different mate had poor oil return to the tank. This turned out be a damaged pump. The circlip had come off the end, bits of mazak had dropped into the timing case and the crankshaft worm wasn't engaging properly with the oil pump gear. We fitted a second hand pump - all good. If your bike has an SRM anti wet sump valve, that's the first thing I'd remove.
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Apologies for my previous post where I got completely muddled with tech terms.
Phew. When i read your original post i thought i'd put some dodgy SRM gear on my bike.
I was going to say that i'd had no problems with my SRM PRV and i also have their own oil pump fitted. Works a treat like a river of oil back into the tank.
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Apologies for my previous post where I got completely muddled with tech terms. Here's what I should have said.....
Interesting...... A mate of mine had poor return to the tank. To cut a long story short, we ended up removing the SRM anti wet sump valve, problem solved! It seemed that the SRM anti wet sump valve was preventing some of the oil getting into the gallery prior to hitting the timing side bush. I suspect the spring was getting coil bound before the ball had cleared the oil gallery. The bike had seized on three occasions prior. Having removed the anti wet sump valve, we ran the bike with no ball and spring (AWS) for a while and the oil flow back to the tank was excellent. We then fitted an outboard Anti wet sump valve (I know, not everybody likes or approves of them) and this prevented wet sumping and did not affect the oil return to the tank. More recently, a different mate had poor oil return to the tank. This turned out be a damaged pump. The circlip had come off the end, bits of mazak had dropped into the timing case and the crankshaft worm wasn't engaging properly with the oil pump gear. We fitted a second hand pump - all good. If your bike has an SRM anti wet sump valve, that's the first thing I'd remove.
Thanks Mate. the previous owner/restorer has fitted an SRM anti wet sump valve in-between the oil feed hose and the crankcase. I removed it and stripped it down, cleaned it but didn't make any difference to the return flow. I'll try taking the spring and ball out.
I've got a table lift coming this weekend so will get back to it once thats assembled.
Forgive my ignorance, I'm new to these old twins, what is a Mazak? Tried googling it but no luck. When you stated gallery do you mean the top of the engine, valves, rockers and pushrods?
Thanks so much for helping with this, I'm learning fast and thoroughly enjoying it.
Else
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Forgive my ignorance, I'm new to these old twins, what is a Mazak? Tried googling it but no luck.
Indeed. I take it to mean bits of swarf and detritus and stuff. *work*
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Mazak more commonly known as Zamak is a zink based alloy that is said to be a good precision casting material . google Zamak instead .
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Mazak more commonly known as Zamak is a zink based alloy that is said to be a good precision casting material . google Zamak instead .
Aha, that makes sense, thanks.
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Apologies for my previous post where I got completely muddled with tech terms.
Phew. When i read your original post i thought i'd put some dodgy SRM gear on my bike.
I was going to say that i'd had no problems with my SRM PRV and i also have their own oil pump fitted. Works a treat like a river of oil back into the tank.
That was what I was expecting to see but maybe that won't happen with a standard pump. I believe I've read somewhere that the SRM pump is higher capacity.
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That was what I was expecting to see but maybe that won't happen with a standard pump. I believe I've read somewhere that the SRM pump is higher capacity.
I was quite surprised when i saw the oil return with the SRM pump fitted.
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Hi everyone,
Around 1970 BSA upgraded the A50/65 oil pumps using larger gears, they also introduced iron body pumps late in the day.
Apparently when BSA closed there were a thousands and thousands of the larger pump gears leftover. These gears wound their way to SRM who took on the manufacture of new pumps incorporating the original gears...
I must have been one of the first customers of the blue pumps and have fitted several more over the years to other peoples A10's all without issues.
A couple of years ago I did an engine rebuild on an Ariel Huntmaster, at the time SRM pumps were out of stock , the owner ordered a "hepolite" pump. The first one sent i rejected due to incorrect drillngs where the body bolts broke into the oilways, the pump was replaced without issues, and I was told to bin the reject.
The Ariel showed great oil return and has run great, however it has taken to wet sumping if left for too long.
In spite of CB's issue with the A65 nrv mod all the engines I have been involved with that have the mod have not had problems.
Fitting the mod requires very careful assemply as it is easy for the gasket to impinge on the ball seating even the improved gasket available. I cut my own gaskets that are snug around the studs to keep them in place while fitting.
John
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I've always known the material that BSA used on their oil pumps as "Mazak" and is the same zinc pot-metal that BMC and Ford etc used for door handles years ago.
There's no problems with it other than it "grows" dimensionally and becomes stiff to turn (or even seizes) when left immersed in dirty oil, and becomes very crumbly.
Makes me cringe when someone posts that he's found some old BSA that's stood in a barn for fifty years and when he asks would he ought to do, some knob will always suggest he puts clean petrol in it and kicks it over. That's the quick way to destroy the pump, it's driving gears and the engine (if it does start) if the pump has nipped up, as they usually do.
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yes rex but the name is possibly a blighty thing and known as mazak , it is german zink - aluminium magnesium and kupfer - copper - zamak is what comes up in all the searches i have done. so maybe blighty re named it magnesium - zink first as blighty would do.
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Rex is on the money there. Just giving that barn find bike a good kick is a recipe for disaster. Even when left on the shelf these pumps lock up.
To dismantle a seized pump without damage a little bit of heat makes it easy, the idle spindle usually falls out on a well worn pump, the gears require gentle persuasion to emerge.
As a kid, I remember Dad negotiating on a Morris Oxford. The chromed hinges on the boot lid had "bubbles" where the Mazak castings were starting to crumble under the chrome. So the longevity in use was questionable back then, but for a manufacturer it ticked all the boxes, and to last this long was never considered. So it got used on our oil pumps.
Wikipedia gives the story, reckon Mazak was the UK trade name.
Swarfy.
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Pot metal hates moisture and will grow and crumble if left dry in air or in an engine with dirty oil, full of emulsified water, condensation etc.
If you are storing a pump for later use, strip and clean it, run fresh engine oil through it then leave in a jar under clean oil or at least in a zip lock sealed bag to keep moisture away and it will be fine.
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This won’t add anything to the expert testing advice already offered, but does provide a visual of what I believe to be the proper oil flow. I made this video (gulp!) 16 years ago.
https://youtu.be/SfJ2zigEbqo?si=hg1BMogGexPSySHZ
Richard L.
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Morning all.
Good news, it’s working nicely now. I removed the SRM nrv and took the ball, spring and seat out and refitted it. I now get a good flow of oil back to tank.
My only concern is wet sumping. What damage does it cause? The bike isn’t going to be used every day, or every week. Probably once or twice a month through the summer but will sit unused through the winter months.
It has a drain plug in the sump cover so I will check it before each ride. What should I expect to be a reasonable quantity of oil after leaving standing for a couple of weeks say?
Thanks in advance to all you gurus, I’d be lost without your help.
Else
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On standing there is a natural tendency for oil in the tank to flow into the sump via the pump, the timing bush and from there onto the big end bearings. The oil way branches to the PRV....(Pressure Relief Valve the big nut on the crankcase front).
The anti- wet sumping valve is situated between the pump and the timing bush. It is a simple spring loaded ball, which moves under oil pressure to open the oil way to the timing bush. It is supposed to "hold back the tide" when the engine is not running. Only accessible with the crankcases split
This oil drain down can be minimal on a bike with a good pump and bearings, to the other end of the spectrum where the oil tank empties in a few days.
Used every day a smokey start for a few moments is tolerable, but if irregular use is the norm, draining the sump before start up is the way to go. Too much oil in the sump will reveal every weak gasket and get complaints from the neighbours due to the smokescreen.
As a rule of thumb, checking the oil tank contents should be part of the start procedure, no oil...... It's in the sump. On starting the return should be strong and steady, as there is always some degree of drain down reducing to a gulp as the sump clears. Good motors do this quickly, not so for the majority running less well fettled machines.
Swarfy
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Else,
I removed the SRM nrv and took the ball, spring and seat out and refitted it. I now get a good flow of oil back to tank.
*????*
Please confirm what you have removed?
Was there a ball and spring behind the SRM oil pump?
What seat?
I hope you have not removed the PRV ball and spring *problem*
John
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I have a standard oil pump and there is just the 4 open ports behind it.
The SRM non return valve is in the feed pipe from the oil tank to the crank case to stop it wet sumping. When you take it apart there is a ball, spring and a removable seat that has an O ring around it.
Else
mod edit: renamed the nrv to save confusion
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Hi Else,
Jeez, you gave me a fright when i saw your last post. *eek*
The correct abbreviation for those is ASV
"Anti sumping valve"
I know that SRM would never sell or fit such
a horrible nasty POS *ex*
Even though they must have made a living repairing the damage caused by them *????*
If you had told us at the start there was one fitted , the instant response would have beet to bin it *bright idea*
John
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Hi Else,
Jeez, you gave me a fright when i saw your last post. *eek*
The correct abbreviation for those is ASV
"Anti sumping valve"
I know that SRM would never sell or fit such
a horrible nasty POS *ex*
Even though they must have made a living repairing the damage caused by them *????*
If you had told us at the start there was one fitted , the instant response would have beet to bin it *bright idea*
John
Thanks for the info John.
The ASV has SRM stamped on one side with an arrow to show direction of flow. I’ll attach a picture of it in situ. I will also attach a picture of the ball, spring and removable seat just for reference.
Hopefully I won’t get too much wet sumping as the pump is in relatively good condition so shouldn’t let too much oil seep through when standing.
Else
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SRM ASV in situ and the internals, ball, spring and removable seat (o ring removed).
Else
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Apologies for my previous post where I got completely muddled with tech terms. Here's what I should have said.....
Interesting...... A mate of mine had poor return to the tank. To cut a long story short, we ended up removing the SRM anti wet sump valve, problem solved! It seemed that the SRM anti wet sump valve was preventing some of the oil getting into the gallery prior to hitting the timing side bush. I suspect the spring was getting coil bound before the ball had cleared the oil gallery. The bike had seized on three occasions prior. Having removed the anti wet sump valve, we ran the bike with no ball and spring (AWS) for a while and the oil flow back to the tank was excellent. We then fitted an outboard Anti wet sump valve (I know, not everybody likes or approves of them) and this prevented wet sumping and did not affect the oil return to the tank. More recently, a different mate had poor oil return to the tank. This turned out be a damaged pump. The circlip had come off the end, bits of mazak had dropped into the timing case and the crankshaft worm wasn't engaging properly with the oil pump gear. We fitted a second hand pump - all good. If your bike has an SRM anti wet sump valve, that's the first thing I'd remove.
I had an engine SRM end fed many years ago and had the same problem of oil not returning properly. I also removed the ball and spring from the back of the oil pump and fitted an external AWSV. It has since done almost 100,000 miles with no recurrence of the problem.
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Just to recap. If I'm understanding the main thread here we are saying that the SRM ASV, an accessory which is fitted in the 'Feed' line before the oil pump is actually starving the oil pump of oil to the point that this showed up as a reduced oil return? Reduced because insufficient oil was being supplied in the first place with attendant low/intermittent oil flow and pressure to the engine bottom end!
Or could it be a sign that the oil pump is below par and not able to draw hard enough on the feed line to open the ball against the spring?
The original one behind the oil pump is on the pressure side of the pump and should never cause an obstruction to oil delivery into the main gallery.
Are these still being sold by SRM's? They deserve to hear all about this.
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The issue there is that the pump doesn't "draw" on the feed line. It's gravity fed.
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Thanks for all the replies and helpful comments.
Just want to say that there is very good flow of oil back to the tank now cold and hot. It is an almost continuous flow rather than the intermittent spurts that I used to get with the ball and spring fitted. I'll worry about wet sumping if and when it happens.
Else
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Shouldn't be continuous after the first minute or so of running after a start up.
Granny's eggs again, but the scavenge side pumps more than the delivery side.
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Hi Else,
That ASV must date back to when the original SRM company was owned by Steve McFarlane *????*
I know the current SRM guys would not make or sell them.
That design was originally sold by "Bri Tie"
Polly Palmer was the owner
John
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Hi Else,
That ASV must date back to when the original SRM company was owned by Steve McFarlane *????*
I know the current SRM guys would not make or sell them.
That design was originally sold by "Bri Tie"
Polly Palmer was the owner
John
Thanks John, I understand.
Else
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Bit of trivia:
Steve McFarlane's initials = SRM.
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Also note that Stephen McFarlane no longer owns SRM, but works privately making electric starters for BSA A10s. And good gear too - I have one in my Flash
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Steve Ronald McFarlane ;)