Author Topic: SRM Oil pump  (Read 5497 times)

Offline A10 JWO

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SRM Oil pump
« on: 27.04. 2013 15:47 »
After reading Dunney's oil problems, I thought I would post this thread.
After five weeks standing I fired up my 1954 after forgetting to drain the new SRM sump. Grey smoke every where !!! Not a problem I know it wet sumps. I drain a few ounces out and left it overnight. the following day the same amount drained out. Time for a new pump I think.
After fitting a new wood burner I have saved enough money on gas for a new SRM Oil Pump. After all the pump is the heart of this splendid motor.
Question
Has anyone got any good advice about fitting the said pump and are there any other issues I should take on board.
 Thanks Lads.

Colin
Essex

Online orabanda

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Re: SRM Oil pump
« Reply #1 on: 27.04. 2013 17:10 »
The new pump might help a bit (if your old one is significantly worn), but the root of our problem is that the non-return valve (a check valve) buried in the RH crankcase half, at the end of the oil pump to timing bush oil gallery (drilling) ain't doing it's job! And unfortunately, there is not much we can do with it as is.

There is also a leakage path across the bearings in the pump, and out through the drive shaft (behind the drive adaptor). Recently SRM have added a shaft seal to their pumps (revised design), and I have also machined a couple of the original BSA pumps and added a seal. I don't believe this is a significant issue in causing wet sumping, anyway. If you buy a new SRM pump, it should have a shaft seal (nice).


If the integrity of the check valve was good (no damage to the seating face in the aluminium case, or to the hardened ball, or any shit between the ball and face), then leakage across the gear pump can't get past it. Unfortunately the long and extremely light spring often doesn't hold the ball square against the seat, and I suspect the spring is too light to hold the ball closed against the weight of the oil. therefore, the check valve doesn't (or unreliably) work, and the rate of wet sumping is relative to the clearances across the pump, and the viscosity (thickness) of the the oil. Sometimes you will shut the engine down, and it might seal; most times it doesn't (and our bikes all wet sump at a slowish rate); ie the rate the oil can leak through the pump, across the ineffective check valve, and between the crankshaft journal bearing and the inner bore of the bush AND sometimes the crankcase and the outer diameter of the timing side bearing.

Only the last few weeks I have been checking this leakage issue, on one of my bikes. The clearance between the crankshaft journal and the bush is within tolerance; only 2,000 miles on the bottom end, and the oil is CLEAN. The crankcase had 0.012" machined out of the bore for the timing bush before the hole would clean up (concentricity); yep the OD on the crank case was out of round! I discovered this when I removed the oil pump and blew air into the bearing oil delivery drilling (the same one which the check valve resides in). Unexpectedly, I got sprayed with oil which got blown out of points between the bush OD, and the crankcase.

So, I check the crankcases for concentricity in the timing bush bore, often they are out of round (high mileages or hard use I suppose is the reason). Then machine them until they clean up (are round), then machine a new oversize bush, and shrink in. Then final machining of bushing ID, to suit crank shaft.

Anyway, back to the oil leakage issue. I removed the sump plate, and observed the rate of leakage onto the bike lift over several days.

Then, removed the oil pump and squirted clean oil into the pump delivery port (across the check valve), and prodded the check valve open. I noted that the very light spring is so long that the ball often deflects sideways, and as a hydraulics engineer, if this arrangement was in a system I was involved with, I would give it the Order of The Royal Rhubarb. I estimate the existing spring as not more than 1 psi force; a 5 psi spring could be used here without any detriment to the lubricating system (the check valve is upstream of the bearings), and it would keep the ball securely against the seat when the engine was stopped.

OK, so re-fit the oil pump after attempting to assess and perhaps clean the check valve, and wait a few days. The results; no change - same size puddle under the bike, and some oil also from the timing side, under the oil pump.

Next step; fit blanking plate with solid gasket in place of the oil pump. This blocked the oil supply  from the tank, and revealed the rate at which oil will leak down between the crankshaft journal and the timing bush, and the big end bearings.
 Result after a few days: same rate of leakage, but without the oil pump blocking the view, I can see the leakage into the timing cover is oozing from between the crankshaft journal, and the bushing ID.

I would expect the same rate of leakage (drain down) on the flywheel side of the timing bush.  Eventually, after about 4 days of wiping oil up from underneath the bike, it ceased all together. This is because the crankshaft galleries, and the drillings in the case, had finally emptied. This exercise satisfied me that the bottom end clearances were OK; no major rate of leakage.   

So in summary, if the built-in non return valve was effective, the engine wouldn't wet sump, regardless of the condition of the bottom end, or the leakage across the oil pump.

A weakness with the existing non return valve, is that the ball seats on the edge of the hole drilled in the (soft) aluminium. Any mark / blemish on this face, and the oil will leak through. therefore whenever apart, the ball should lightly be tapped into the hole, to re-seat. Be careful; hit it too hard, and the seat could be damaged! The A65 arrangement is better, because the seat is the hole in the base of the oil pump, and can be inspected easily, and re-worked. A hardened (replaceable) seat would be prefer

It is worth considering a replacement spring for the existing arrangement, but it has to compress enough to allow the ball to travel past the oil hole in the side of the crankcase (oil way to the timing bush), otherwise the flow could be blocked to some degree. I.e, the closed length of the heavier spring (which will be made of thicker wire) must equal or exceed that critical measurement - not hard to check during installation, but needs to be investigated.

What to do:

A50 / A65 engines; BSA repositioned the check valve so that it sits underneath the oil pump and is therefore readily accessible. Until recently I have had no experience with these engines, but now have an A50, so will have a closer look at their arrangement.

Do the unit twins wet sump as badly as the pre-unit? I would have thought not.

Has anyone modified A10/ A7 engines to copy the unit twins system?

I am starting to think up a way to solve this problem, and am putting together an A7 bottom end, so watch this space!

Richard


 

Offline A10 JWO

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Re: SRM Oil pump
« Reply #2 on: 27.04. 2013 17:23 »
If there was an award for the best reply, you would win. I thanks you for that. I will read your answer a few times before it all sinks in. I hope other people can take note of your good sense and wisdom of the gents motorcycle. Will update you in good time.

Kind regards Colin

Online Brian

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Re: SRM Oil pump
« Reply #3 on: 27.04. 2013 23:41 »
Excellent post Richard, its good when someone does some controlled tests to see what is actually happening as opposed to what people "think" is happening.

I have owned A65's and a A50 and as a rule they do not wet sump as badly as the A10/7's and if one does its simple to cure with the ball valve being behind the pump. Just why BSA buried the ball valve in the crankcase half on the A10/7's is anybody's guess.

I believe the A10/7 can be modified to have the ball valve behind the pump but I have not done this myself.

Some time back I did look at this problem but didnt go anywhere with any of my ideas. One idea was to have a ball valve enclosed in a sleeve that screwed into the crankcase from the pump side, a independant valve unit that could be removed. Maybe there is a small one way valve unit available that could be adapted ?

Your findings back up what I find with my bikes, that is the problem is intermitten. My A10 can sit for three or four months and not wet sump a drop, but other times it will fill the sump in a few weeks. I run a filter and change the oil every 1,000 miles so the chances of a foreign body in the oil should be minimul which comes back to the ball not seating correctly for one reason or another.

The downside of your excellent reply is I might have to concede you sandgropers know what your on about.  ;)

Online orabanda

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Re: SRM Oil pump
« Reply #4 on: 28.04. 2013 01:39 »
Thanks Brian,
Unfortunately we have forgotten to play football! Port Adelaide; Boo, Hiss, a pox on them!

As I wrote, I am also considering how to re-locate the valve to the front. Some of the issues are:

there must always be positive seating of the ball
the spring force needs to be increased (small amount)
The  ball must not restrict the oil flow to the oil gallery (drilling) in the side as it moves back (this is one reason they used such a weak and long travel spring in the existing design)

Richard

Offline olev

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Re: SRM Oil pump
« Reply #5 on: 28.04. 2013 03:15 »
Orabanda,
Have a read of this.

http://bsa-a10.hailwood.com/mybsaa10rollerconversion.html

In the middle there is a bit about converting the oil return to the A65 type.
I don't understand it but I think Beeza Bill (rip) went at least part way down this road you are thinking about.
cheers

Online muskrat

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Re: SRM Oil pump
« Reply #6 on: 28.04. 2013 05:59 »
 I thought I'd seen that before olev. Doesn't srm do one as well?
I had that same conversion done by Dean Harrison over there in WA 22 years ago, $970, but without the valve change.
Cheers
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Offline mayes

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Re: SRM Oil pump
« Reply #7 on: 30.04. 2013 18:17 »
What a brilliant response to the problem had to look up few of the words but great john
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Offline A10 JWO

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Re: SRM Oil pump
« Reply #8 on: 01.05. 2013 16:07 »
Hi lads.
I put several theories to SRM and they were very kind. Their final reply was as follows:-

"The check valve is the last piece in the chain to try and prevent oil seepage, and not much can be done about that, even the A65 with the ball against the pump body will wet sump."

"Our pumps as mentioned have a seal between the worm gear and cavity but also the feed and return cavities are also sealed from each other, these new oil pumps will reduce any oil bypass to almost zero."
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I have ordered a new SRM pump today and will update the group with my findings. I would like to thank Richard and all the other replies. What would we do without the A7 A10 Forum and a pint of course.

Regards Colin
Essex

Offline Topdad

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Re: SRM Oil pump
« Reply #9 on: 01.05. 2013 16:38 »
First up , what a reply ,so indepth and worked through logically going to reread just to make sure it all sinks in. Richard my bikes had the SRM conversion and I'm sure they modified my oil pump to A65 spec ie spring and ball , have you heard that that is the case ? or is my memory letting me down, was 10 yrs ago after all , either way excellent work richard Regards BobH
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Offline A10 JWO

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Re: SRM Oil pump
« Reply #10 on: 01.05. 2013 17:09 »
Question for Topdad.
Hi just wondered how you got on with that SRM pump in relation to wet sumping and performance of the pump overall.

Regards Colin

Offline Topdad

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Re: SRM Oil pump
« Reply #11 on: 02.05. 2013 10:18 »
Morning Colin, simply after reading all the info supplied by richard your own brain (Or at least mine does )kicks in with bits of info that have stuck in the brainbox and unexplained things that happen to your bike over a period of time plus looking at and reading  the post it lined up my 3 remaining braincells hence the question, also slight alarm bells as if they do modify the pump then my pump isn't correct anymore ,the one they may have adapted cracked at the drive spiggot after some time and I replaced with a spare I had and here is another quirk ,when I first put the bike on the road following a full rebuild( including full engine job by SRM ) it was reasonably wet sumping free but at the mo and it seems to me since the other pump was fitted , she's become  incontinent . Again the more I write and think the more sure I am that I did send the pump to them along with C/cases ,crank ,rods and timing cases  I feel a phone call coming on. Best wishes BobH.
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Online orabanda

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Re: SRM Oil pump
« Reply #12 on: 02.05. 2013 10:48 »
Hi Bob,
Unusual for a pump to crack! Can you post pictures of the damage? Excessive side load?

Was the fibre washer in place under the "nose" of the pump? (between the crank case and the pump; the shorter of the three pump mounting bolts passes through the washer).

If the wet sumping is now worse, then the internal leakage rate (between the gear sets and the Mazak housings,)  is greater for your current pump.

However, this might be the only negative issue with the pump; it could still be fit for  the purpose of lubricating the bearings (50 - 60 psi pressure with cold engine, @ a couple of litres / min oil flow for the delivery stage of the pump).

Richard

Offline Topdad

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Re: SRM Oil pump
« Reply #13 on: 02.05. 2013 11:34 »
Will do Richard , kept as a warning against complaceancy and useful paperweight , just spoke to SRM by the way and will have an answer re any work to pump later today .
Yes , the pressure at the tank is very healthy ,just fed up with the constant puddle on the floor of course could be grasping at straws .Best wishes BobH
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Offline A10 JWO

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Re: SRM Oil pump
« Reply #14 on: 02.05. 2013 15:07 »
Hi Topdad. Thanks for getting back. I am keen to know what they say at SRM. I dealt with a guy called Gary at SRM, quite a helpful chap. I got the impression that they are not keen on forum gossip. Lets see what they say. To date I have never heard anything bad about SRM, unlike the company down south that make exhausts that don't fit. ( another story ).

Regards Colin