Author Topic: More BSA oil pressure problems. A real puzzle  (Read 5493 times)

Offline Jeremy

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Hi

I am turning to you guys 'cos I am stumped.  I have owned this bike 25+ years and for the first 15 ran it without this issue.  Its been laid up a long while but I have had it kicked up and running.  What happens is oil pressure drops away too low when the motor is hot.  The motor is heavily uprated and this should not happen.


bsa 2 by TandemJeremy, on Flickr

Engine spec.
1961 10 but actually IIRC A7 crankcase.
SRM end oil fed crank.
Oil filter tapped into the pressure side on the lower front inner timing cover
A65 pump body with A10 worm drive
Triumph type oil pressure relief valve set to 50 psi.
Big ends have only done a few thousand miles since checking
Running on multigrade.

Symptoms - when hot the oil pressure drops. 
At start up from cold the gauge reads as you would expect - 30+ at low revs, rising to 50 as the revs rise then not rising any more as the pressure valve opens.  Once properly warm however it drops to 10-15 at revs and zero until you get it spinning.  No nasty metallic noises.

I have tried
different pumps, different relief valves, different oil filters.   All oilways have been flushed, the seal in the outer timing cover has been replaced.   Oil returns to the tank normally, all gaskets have been replaced.  Somewhere when its hot oil is getting out of the high pressure system but only into the crankcase.  the pressure gauge is tapped into the remote filter housing on the feed side.

So - any thoughts?  My latest suspect is the threads the oil pressure relief valve screws into - they appear slack in the at the end of the threads could oil be escaping past the sides of the valve and duping backing the crank case?  If so how can I test this or fix it.  any other ideas?

Help save an old lady from the depths of a lockup.

Ta

Jeremy

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Offline Jeremy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #2 on: 24.07. 2013 12:15 »
Ran it on straight 50 oil - higher pressure when cold but not when hot.  It ran on multigrade for years with no issue

Offline A10Boy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #3 on: 24.07. 2013 12:29 »
I don't understand why the oil filter is tapped into the pressure side? Presumably the filter outlet is connected into the return side? If so, this will give a pressure bleed off through the filter.

Are you sure you got that right, or am I misunderstanding your post?
Regards

Andy

1960 A10 - Black Golden Flash
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1974 Kawasaki Z1a
Yam XJR 1300

Offline Jeremy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #4 on: 24.07. 2013 12:39 »
The filter is inline on the pressure side - the oil is routed from the pump to the pressure releif valve then thru the timing cover to the filter and then from the filter back to the timing cover and on to the crank - so the crank gets cooled filtered oil.  You can see the oil filter sitting on the lower engine mount.  The gauge take off is on the pump side of the filter.  Again the bike has run with this set up for a long time with no issues.  Its dumping all the high pressure oil somewhere and no sign on the outside or the timing covers

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Re: More BSA oil pressure problems. A real puzzle
« Reply #5 on: 24.07. 2013 12:51 »
Hi obviously you know your setup and fowoll your logic but I would have expected a filter on the return side particularly has I seem to remember another post where it was emphasized that fitting on the feed would restrict the flow but my memory may be at fault. Have you checked the guage ?could be  duff.Jeremy great thing about this forum is that there will be someone on within hours who will know what is going on, I can only suggest checking pump ,relief valve and gauge for now, regards and welcome again BobH. 
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Offline A10Boy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #6 on: 24.07. 2013 12:57 »
From memory, the quill feeds only the big ends and the bleed off prom the PRV goes to the camshaft. So, without looking at the bike, it sounds like it could be either worn big ends, [how did you check them?], a stuck PRV, or leaking threads on the PRV as you say. - Is the pump gasket sound?

I have to say, I don't like the idea of having the filter in line on the pressure side, any failure of a pipe joint or a stone puncture in the filter cannister and bang, you have instantly lost all pressure. As has been said, the usual way is to fit filters in the return line away from pressure.

Regards

Andy

1960 A10 - Black Golden Flash
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1974 Kawasaki Z1a
Yam XJR 1300

Offline Jeremy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #7 on: 24.07. 2013 13:06 »
There are advantages to the filter placement in that the crank gets the cool filtered oil - and on the return side you can get scavenge issues.   I have never had any issues with it.

Big ends - the engine was stripped and the bottom end checked by SRM not that many miles ago.( But a good few years)  It ran properly after that.  I also tried pumping the crank full of oil via the quill so the big ends were pressurised and it held pressure even when hot.  No reason to suspect the big ends

I did replace the pump gasket with a new one and that made no difference

I took the bike off the raod for a cosmetic rebuild and had issues on start up which was traced to a faulty guage.  However I fiddled with loads of other stuff before realising the gauge was at fault and appeared to get a different fault once a new guage was fitted.  the gauge reads as I would expect on cold oil including the PRV kicking in at 50 psi.

Offline A10Boy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #8 on: 24.07. 2013 13:22 »
OK, my view is that there might well be nothing at all wrong with your motor!

You might not agree with this, but oil pressure can be notoriously low on a hot motor. The important thing is that the pump/oil system is pumping a sufficient quantity of oil to the big ends. The pressure is largely irrelevant. There are many people here who have fitted oil pressure gauges to perfectly good engines and then given themselves sleepless nights wondering where the pressure goes when the engine warms up. What range is your Gauge, you are reading 50 plus, but how accurate is it down at the 3-5 psi range which is where a hot engine operates?
Regards

Andy

1960 A10 - Black Golden Flash
Plus
1974 Kawasaki Z1a
Yam XJR 1300

Offline Jeremy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #9 on: 24.07. 2013 13:32 »
It used to run much higher pressures.  I agree with you to some extent - there has been no nasty knocking noises from the big ends but something has changed.  It used to be 20+ psi at idle and 50 when riding.  Now its 20 and next to nothing

Offline A10Boy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #10 on: 24.07. 2013 13:42 »
Why not try a fine gauge at 0-5psi range? Warm the engine on the gauge you have, then swap to the fine gauge and let it idle to see where it's at? If you didn't have a gauge at all, you would be quite happy with the bike......

You can use the search facility here to find other posts regarding oil pressure, it might give you some comfort.

Good luck
Regards

Andy

1960 A10 - Black Golden Flash
Plus
1974 Kawasaki Z1a
Yam XJR 1300

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Re: More BSA oil pressure problems. A real puzzle
« Reply #11 on: 24.07. 2013 14:12 »
I've not seen an SRM set up but I had one with an outrigger from the pump to the end of the crank. I found that when hot the seal would soften and blow off pressure, caused by crank flex. I replaced the seal with a bush and had no more problems. (Mind you it was a very light crank doing 7500 at 13:1 comp)
Could the bearing be not as tight in the case as it should be and allow a pressure drop when the case expands?
If it is the PRV thread, is it possible to put a thin O ring in the case for the thread to but against, stopping any oil going that way? Or make a plug out of an old PRV (so it won't allow oil to pass). Once it gets to the low oil pressure stage, swap it in and watch the pressure. That should eliminate the PRV from being a suspect.
Way past my bed time. Goodnight. *sleepy*
Just saw A10Boy's post. Mine runs 20psi at idle stinking hot.
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Muskys Plunger A7

Offline Jeremy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #12 on: 24.07. 2013 14:15 »
The quill seal into the crank has been replaced and anyway oil is not going into the timing cover I don't think.

Online orabanda

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Re: More BSA oil pressure problems. A real puzzle
« Reply #13 on: 24.07. 2013 15:11 »
Jeremy,
A couple of comments to assist you in diagnosing the situation.
I find it easiest to solve problems  by coming back to basic principles.

Firstly, pressure is created by resistance to flow. The pump does not create the pressure you are measuring; the pump only produces oil flow. It is the resistance in the oil flow path, that create the pressure you are measuring.

Think of a garden hose. When turned on and pouring onto the lawn, there is maximum water flow out but no velocity (the stream falls at your feet). But, as you progressively block the end with your finger, you can feel the pressure (back resistance) grow, and a diminishing stream of water comes out (at an increasing velocity).

I recently measured both sections of the A10 pump, and calculated that the displacements are:

Crankshaft supply section:  Theoretical flow of 4.14 l/min @ 6,000 rpm
However, because of (necessary) internal clearances between the gear teeth and the mazac housing AND between the sides of each gear and the end plate (and the mazac housing on the other side) the ACTUAL flow will be less than theoretical. This is expressed as volumectric efficiency, and I expect the A10 pump in good condition to produce only 85% of its theoretical flow (at best). I.e the pump has a volumetric efficiency of 85%. This means that the actual flow of the pump section is 3.52 litres / min @ 6,000 rpm, which is 85% of the theoretical flow.

Note that the flow is directly related to shaft speed. Therefore at 3,000 rpm (a typical riding speed), the crankshaft oil supply section of the pump will produce 1.75 litres / min AT BEST.

The following factors will all act to reduce the volumectric efficiency of a pump (resulting in less ACTUAL pump flow), and often more than one are having an effect:

- Oil Viscosity (the thickness of the oil). Viscosity is a measure of an oil's propensity to flow. The thicker the oil, the slower it flows (the higher the internal friction within the oil molecules). A typical engine oil with an ISO rating of 100, will have a viscosity of 1,200 centistokes (cSt) at 5 degrees Celsius (a cold start condition), but will have fallen to 30 cSt at 70 C (a running engine). you can see that the viscosity is almost a factor of 10 times lighter (it flows almost 10 times easier) This means that the thinner oil will escape more easily through clearances such as across the pump gear sets, big end bearings, timing bush (or bearing),and the OUTSIDE (fixed) diameter of the timing bush.

- Wear across rotating components. This includes the big end bearings, and their journals, the timing bush (or bearing) and its journal, the oil pump end plate, and inner face the gears run against, the gear teeth and the mazak housing. As these clearances increase, the oil finds it easier to leak away Remember: Flowing fluids take the path of least resistance. Like us; we all take the easiest path!

- Temperature. Internal clearances become greater as the engine heats up. This includes the big end bearings, and their journals, the timing bush (or bearing) and its journal, the oil pump end plate, and inner face the gears run against, the gear teeth and the mazak housing.

- operating pressure; The greater the pressure, the greater the leakage rate. However not relevant in your instance, as the pressure is falling because:

The engine warms up / eventually reaches operating temperature. The temperature increase causes the oil to thin dramatically, which increases the internal leakage rate from every potential location. It also causes the pump volumetic efficiency to fall further as well (pump flow reduces). The raised engine temp also causes the dynamic (operating) clearances to increase at the same time, which further increases the rate of internal leakage(s)

How do you notice the rise in internal leakage (and probable reduction in pump output flow)? - the oil pressure falls!

If you increase the revs, the pressure will increas a little, as you have increased the pump output flow.

Th relief valves in our bikes are set to approximately 50 psi. You only see this pressure on the gauge when the rate of pump output flow exceeds the rate of internal leakage. When the engine is hot and the oil is many times thinner (slips away easily) and the clearances are greater (larger leakage paths), the oil pressure falls as the internal leakage rates increase. When (if) you have no pressure, then the leakage rate exceeds the pump output flow rate. 10 psi seems to be an acceptable pressure when the engine is hot; 0 psi would worry me!

I would check the integrity of the oil seal delivering oil to the quill as well.  If the wrong type of seal has been fitted, then it could fail at apressure less than the 50 psi you will get when cold. Many lip seals are not rated beyond 15 - 20 psi; the lip will tear or turn inside out. Further, the (static) OD of this seal is as critical as the lip. Oil could be leaking past if the crush is not sufficient, and a sealing compound has not been used.

Note that the scavenge side of the A10 pump has a theoretical fow of 5.8 l/min @ 6,000 rpm. With volumetric efficiency of 85%, the flow will be 4.9 l/min. This is approximately 30% more flow than the crankshaft delivery section.

Tthe pressure filter installation has the advantage of controlling the oil cleanliness to the bearings. However, as the filter blocks, it will reduce pressure to the bearings. Hopefully the element has a bypass valve. This means that when the pressure on the dirty (upstream) side of the filter reaches the setting of the bypass valve (say 15 psi), the bypass valve opens and unfiltered oil flows through, to the bearings. However, oil pressure downstream of the filter (but upstream of the crankshaft bearings) will always be 15 psi less, than upstream. As the engine wears, and leakage increases, this could result in no pressure at the bearings.

Don't use a non bypass element, as it could block to the degree that there is no pressure at the crankshaft, even at cold start.

I fit a filter to the return line.

Hope this helps,

Richard

Offline A10Boy

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Re: More BSA oil pressure problems. A real puzzle
« Reply #14 on: 24.07. 2013 15:25 »
Great post Orabanda!

Re PRVs
I know form several builds where I have used SRM PRVs that they do have a variance in the thread width [while within spec sir] as do the case threads. You can get leakage past the threads between the two "halves" of the PRV and the cases which would increase with temperature as the oil viscosity decreases. Perhaps you could measure the internal thread in the case as I have done and ask SRM to sort through their PRVs to find a match, or at least one on the high end of the spec tolerance. They have done this for me before quite happily.

Just to clarify, was anything done to the engine between when it had higher oil pressure and now, or did it just happen one day?

Musky is to be complemented on his marvelous oil pressure, however I don't believe his numbers are representative of the typical A10 engine. These engines are well known to have low OP at idle when hot as were most engines of the era.
Regards

Andy

1960 A10 - Black Golden Flash
Plus
1974 Kawasaki Z1a
Yam XJR 1300