Static flow through oil pump

[barrydevon]

Long story short, I bought a long stroke A7 plunger. Oil mysteriously disappeared and it went bang. (Oil system seemed to work properly with flow back to tank prior to this).Expensive rebuild later and I have just put the oil pump on. Put a little oil in tank to check for leaky junctions etc (with timing case off), and next day noted the oil flowed out over the top of the pump body. Does this mean pump is not stopping the oil and it will wet sump instantly if tank filled or will the flow stop when enough is sat in the various ports and chambers in the engine. My first A7 so just don't know the quirks. Any advice/ guidance other than "get the short stroke, parts are cheaper and easier to find"?

[limeyrob]

A very interesting question that's been bothering me too.  A few months back I rebuilt my A10 SA engine and spent some time seating the wet-sump valve seat/ball/spring and was confident that the bike would not wet sump.  I refitted the old oil pump but stripped and lapped the faces so I was fairly sure about that too.  When parked the bike will put a jam jar of oil in the sump in 2 weeks.  I'm now thinking its running though the pump which begs the question "how is the oil pressure?".  I have a spare oil pressure relief valve and I'm considering drilling and tapping the spare for a gauge.
I took the timing cover off to do the timing after it had been standing a few weeks.  A lot of oil was in the timing chest witch suggests that it is running though the pump not the wet sump valve.   The problem is that if the pump is peeing oil out it will still look good on the oil return but it will be by-passing the crank.

[muskrat]

G'day Barry 
Sounds to me like the pump body is distorted or the gasket isn't sealing. Pull the pump off and lap the base with wet&dry on glass. Use a new gasket (the ones from SRM are best) making sure the bit under the "nose" is the same thickness.
Cheers.
Now get over to Introductions and give us your story.

G'day Rob.
There will always be oil in the timing case till it reaches the hole into the crankcase.
Cheers

[Beeza]

I noticed on one of my rebuilds that oil was passing over the pump too, on close inspection of the gasket supplied, it was a loose fit, that one of gasket holes slightly overlapped from the oil supply hole to the bolt hole, allowing oil to leak out through the bolt spring washer. The newer SRM gaskets seem to fit better.
Thomas

[JulianS]

There are some dreadful pump gaskets on the market.

Photo shows SRM gasket on the left which fits perfectly, genuine BSA top right which fits perfectly when a thin fibre or gasket paper washer is used on the pump nose and bottom right nasty poor quality horror which could seize your bike.

The oil holes in it are too small and the mounting holes are too large allowing the gasket to move and mask the oil holes in the pump and crankcase. These oversize mounting holes are needed for the unit singles where the pump body was dowelled to the crankcase, but the oil holes still too small.

[muskrat]

G'day Garry.
Note Julians pic of the SRM gasket has the feed hole larger than the other 3. It's for the "A65 type" where the non-return ball sits against the pump. No problem fitting on our A7 & A10 motors. I recommend getting one.
Cheers

[limeyrob]

This morning's task? Order the SRM gasket - well 2 since I'm bound to mess one up

[chaterlea25]

Hi All,
I don't know if the long stroke pump is different to the later pumps or not?
If the same refer to the recent topic on buying a new pump or not.

Old mazac pump bodies are well worn at this stage and often porus as well
Not worth the risk in re using them in my opinion

John

[limeyrob]

Just ordered the SRM gasket, I'll start with that.  Of course I realized I'd not got the correct spanner so I've just got a 25/32 off e-bay.  It didn't matter before but now I know they exist I had to have one

[Swarfcut]

Just revisited this topic in the light of new member Steak-Pudding's conundrum.

   Oil drains down into the sump, and as stated, used every day this is no problem as the scavenge side can cope with the small amount every day. Leave for a while and the whole tank can drain down. Modified sump plate with a drain or stop tap in the feed line are the usual easy fix, both have their champions and doom mongers.

 The designed barrier to this drain down is the so called "anti wet sumping valve" which is situated between the pump pressure outlet and the timing bush. But even with a perfect seal on this valve, oil can seep through the pump, the exit being via the drive spindle. BSA tried to remedy this on the later A65 Unit models...  these pumps have a cast iron body and an O ring seal seal on the input gear shaft.

 With a worn pump, and a poor seating valve you're on a looser to start. Let alone a porous pump body and a poor gasket. A worn timing bush will allow oil to cascade over the pump on a running engine, yup, seen that, rather than going to the big ends. So if the valve leaks, here is another easy way down. And yes, oil can also escape around the outside of the timing bush if you are unlucky to have a poor crankcase, always worth a pressure test on any rebuild using a standard type bush set up.

 Plenty on the Forum about the foibles of this dry sump system, sleepless nights guaranteed if you have a problem.

 Hepolite/Wassell also offer a new pump, this has a cast iron body, so is a possible alternative to the alloy bodied SRM pump.

 A7 Longstroke pump is the same, so later pumps and gaskets fit.

 Oil pump cavity fills with oil from the timing bush, level is up to the keyhole slot, surplus drains through back to the sump. Surprises new folks when they take off the timing cover and it all pisses out.....

 Swarfy.

[limeyrob]

For no particular reason I was looking at the mods Mead and Thomkinson did to their endurance B50s and one caught my attention:
They said they made a 1" thick all plate to lower the sump plate and lengthened the pick up pipe to match.  They did this so that the return pump was always picking up a solid oil flow and not pumping in froth as this had been a problem at sustained high revs.

[Rex]

Surely the pump will always pump froth if the scavenge side is greater than the supply side? Even with a deeper "sump" it'll soon catch up.

[limeyrob]

Well I tend to agree but it seems they made a number of mods. The made big holes between the chain case, gear box and crankcase so the same oil was used throughout.  They said the problem was the difference in capacity between the scavenge and feed was too small to cope with the volume of hot aerated oil and so the level would rise.  The deeper sump seems to have acted as de-aerator so pumping mostly oil the scavenge could cope.  These were amazing bikes beating 750's in 24 hours endurance races.
Rather than me wittering on and making a hash of it here's the source:
https://www.b50.org/mead.htm