The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Jeremy on 24.07. 2013 11:43
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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.
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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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dont know about others but I use Castrol straight 40
XXL 40
http://www.castrol.com/castrol/sectiongenericarticle.do?categoryId=9014107&contentId=7027099#7094384
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Ran it on straight 50 oil - higher pressure when cold but not when hot. It ran on multigrade for years with no issue
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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?
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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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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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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.
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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.
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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?
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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
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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
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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.
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The quill seal into the crank has been replaced and anyway oil is not going into the timing cover I don't think.
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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
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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.
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Great post Orabanda!
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?
Yes - due to being mislead by a faulty gauge I swapped then swapped back the oil pump, then later changed the oil pump gasket. I also swapped around with different PRVs and replaced the filter element. I also had the timing cover off and on a good few times and have replaced the quill seal. which goies into an ally block with oilways drilled into it. some where in all this I introduced a fault but now cannot eliminate it.. the more I think about the more I think its the fit of the prv. Especially if this fault is one that is known.
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Jeremy,
Unlikely to be the PRV if you can get the pressure when cold.
i would have a very close look at the quill seal.
Regards,
Richard
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its a possible leakage round th threads as in a10boys post. You can feel the threads deeper into the crankcase are loose as you wind it it. Quill seal was changed with no change in symptoms
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Possible, but they would have to be REALLY loose threads; ie. tapped significantly oversize.
When you tighten the PRV up, against the fibre / sealing washer on the outside, the thread form on the prv is pulled up against one side of the thread form in the crankcase, which improves the sealing significantly.
Regards,
richard
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I'm not saying this is the cause, but it was raised in the original post. But, I've seen as much as 28thou between the OD of a PRV and the ID of the case threads!
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HI All,
Jeremy, There are two "O" rings fitted to the hollow dowel that transfers the oil to the outer timing cover block on either side of the inner timing case on my SRM engines, are these in place? or is your set up different?
Is the seal in the case face correctly?
Another possibliity (remote) could be that the timing side needle roller bearing is loose in the crankcase
as I believe this blocks off the old feed to the original bush ???
Richards explanations are valid but ignore one vital element, centrifugal force !!!
The spinning of the crank actually sucks in oil to the bigends
Another reason that baffles people with oil pressure gauges fitted as they watch the pressure drop as the revs rise unless the system is bleeding off through the PRV
A symptom of change over time without milage can also be due to the detioration of the mazak of the pump body
causing leakage through the body and at the end plates
I would send the pump to SRM for testing on their rig to eliminate this from the possibilities
HTH
John
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O rings in place and renewed, quill seal replaced, symptoms persist with a different oil pump ( I have 3)
this is wy I am baffled.
I don't want to have to do a full engine strip but its looking likely right now. Today I shall try the prv see if I can ensure it is sealing properly.
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What I am thinking of doing is puttin fibre washers under the prv so that it bottoms onto those before it is fully threaded in - then I will know that the prv is sealed at the bottom to the crankcase. I can't see any issue with doing this other than it might leak oil around the threads at the top of the thread.
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Ok, I'll throw this in since after a winter's lay up I gawped at my oil pressure gauge's low pressure reading once under way in amazement for a while and checked and changed things until I was blue in the face until one day I decided to concentrate on the suction side of the oil system. I found accumulated oil gunge at the bottom of the tank which I cleaned out, blew through the internal pipe inside the tank and changed the oil feed hose for one from SRM and .......65'ish psi at start up, consistent 55psi hot on the road, 30'ish psi at idle. Happy bunny time!!!!
P.S. The engine is in good nick, uses an SRM end feed, PRV and oil pump, 40 grade oil and oil cooler and filter on the return side.
It worked for me.
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alanp - was your engine giving full pressure when cold before cleaning the sludge out? Or where the pressures low consistently? This is what baffles me as its fine until it gets hot then the pressure dissappers
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Keep the ideas coming tho chaps - it all helps - ta
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Jeremy,
The zero pressure is a result of the leakage path(s) within the engine being great enough that all of the oil the pump is capable of producing when the engine is hot, is leaking away into the sump.
There might be only one significant leakage point, or it might be a culmination os seval factors which include:
- Oil type (viscosity too light)
-worn big ends and or journals
- worn oil pump
- leaking past the quill
- leaking past the quill seal
- leaking past any of the other flow paths that were added when the engine was converted the needle roller bearing, including the o-rings arond the dowel, and the alloy black which houses the quill oil seal
- potential issues with the quill oil seal (see below):
Has the recess for the quill seal been machined in line with the quill? (is the seal concentric)?
Is the internal lip of the quill seal engaging on the quill? Is the seal installed to the correct position (depth) in the machined recess?
What is the ID of the quill seal?
What is the OD of the quill?
- leaking around the OD of the timing side bearing
- PRV jammed open (unlikely as you can reach 50 psi when cold). I doubt that there will be sufficient leakage around the threads of the PRV.
keep your chin up, and keep looking!
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Hi
thanks for that. the quill seal is new and is a tight fit on the quill - much tighter than the old one. I can check the depth of it but I am sure it is engaging properly. I will check tho.
I ran it on multigrade for many years and multigade is only thinner when cold - not when hot compared to straight oils. Running on 50 straight oil made no difference apart from higher pressures when cold.
the PRV is working properly - you can see it open as it hits 50 psi - ie pressure rises with revs when cold until it hits 50 psi fault exists with different prvs installed
Fault exists with different oil pumps installed and with or without the ball and spring
As said - it used to run fine, I had a oil pressure gauge fault ( reading low at both cold and hot) which fooled me and led me to replace all components in the system and then I realised the gauge was at fault so put a new gauge on to find this fault which I presumably introduced when replacing pump and PRV and so on.
I have no reason to suspect the big ends - check by srm not many miles ago,no nasty noises, crank holds pressure when pumped full of oil from an oil can
I do wonder if when taking the PRV in and out too many times I damaged the thread or it became worn past a tipping point.
Having checked / replaced / substituted every thing I can thank of bar the big ends I am left with a conundrum.
Ho canI check if the PRV is bypassing along its threads?
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"Ho canI check if the PRV is bypassing along its threads?"
As I suggested a O ring would work better than fiber washers, or you could try teflon tape just on the first part of thread on the PRV.
What type of bearing is it? The INA NKIB5906 that was in mine had an oil hole in the outer that needed to be blocked or oil pressure would be lost.
It's gotta be something silly. Were the o rings you replaced exactly the right size? Too big will be as bad as too small. A metric one will look the same as a imperial one but the very slight difference could do it.
We can't see the forest for the trees.
Cheers
ps SR500's have a problem in that the seal only just engages the quill.
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HI
Alan, where did all that sludge come from ???
I now remember something similar happening on a Triumph brought to me some years ago
Jeremy,
A collapsing oil pipe when it gets hot on the suction side is worth a thought????
On the other hand
Why not set up a reverse flow into the engine???
Weird ???
Ok add a T into the feed line to the oil pressure gauge, a pipe from the tee to a pressurised oil feed
maybe one of those pressureised brake bleeding bottles??? or similar
block off the feed from the oil tank
remove the timing cover and block the feed to the block in the outer case, since the crank is holding pressure
remove the ball from behind the oil pump to allow the pump to be pressurised, refit pump
remove sumpplate
pressurise the system
You can pressurise the timing cover block separately if needed
now you can watch where the oil pees out, *idea*
HTH
John
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alanp - was your engine giving full pressure when cold before cleaning the sludge out? Or where the pressures low consistently? This is what baffles me as its fine until it gets hot then the pressure dissappers
Yes, I had full pressure when cold.
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HI
Alan, where did all that sludge come from ???
I now remember something similar happening on a Triumph brought to me some years ago
Jeremy,
A collapsing oil pipe when it gets hot on the suction side is worth a thought????
I used to change oil every year or so and use an inline filter so felt smug about things but didn't remove the oil tank to clear out the bottom of the tank.........also I used a multigrade for a while and then changed back to mono which may have influenced the sludge/gunge formation.
Bear in mind I also changed the oil feed pipe at the same time, i.e. more than one change, so can't be sure which change did the trick, the tank clean out or the pipe. I didn't care really since I got the result I wanted. Suggest both are tried especially as they don't require any more engine parts stripped out which I'm sure Jeremy is fed up with right now.
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Your only on page 2 of your problem Jeremy. Andy just got his problem sorted at page 4.
That's a great idea John. It would best be done with a hot motor and in low/no pressure mode.
I can see Jeremy having a 50 weight shower.
Cheers
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A 50 weight shower - nasty :-)
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It will be a few days before I can have another go at this. I will report back tho
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Well another day spent on this with no change. PRV was definitely sealed into the crankcases. ( o ring, thick washer, o ring and the prv was slightly proud) still lost pressure when hot
I will try the suction side of the system next. any more suggestions?
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I had a low oil pressure scare a few weeks ago. Started her up and had 50Lb for about 10 miles. It started to drop slowly to about 30Lb so I headed home. By then she was struggling to make 10Lb and zero at idle.
Turned out to be the oil pump screws (I don't use studs) had loosened 1/4 turn each. Re tightened them with loctite this time. Problem solved.
I don't think your problem will have anything to do with the scavenge side if that's what you mean by suction. Have you tried a heavier oil, say 40/70 ?
Cheers
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Musky, I'm sure he means the suction side of the pump from the oil tank not the scavenge.
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Indeed - I mean the oil lines from tank to pump.
Teh pump has been replaced (several times as I have 3 to choose from) along with its gasket with no change in symptoms. I could check tightness again I guess
It ran perfectly on multigrade before so should now.
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My ten cents worth: *smiley4*
You stated that you have an A65 oil pump body fitted, is it the late cast iron higher capacity type or are your pumps all mazak earlier type. From memory the late pumps had "O" ring sealing the shaft inside the pump to stop oil transfering between the feed and scavange gears inside the pump if the pump body is worn in the shaft area, is the oil leaking between the 2 chambers when hot. Yes I know you have changed the pump with no result but if the late type pump has the "O" ring missing in all of your pumps that might be your problem.
Now this problem has just happened and you say that you have not changed anything prior to the low oil pressure when hot problem rearing it's head, a couple of bad things that could cause this, one has been mentioned worn big ends, or maybe the sludge plug leaking or if later big journal crank the centre sludge trap flywheel bolt that is drilled into the crank's oil chamber loose or leaking. Muski mentioned the outer part of the combo needle roller bearing being loose and not sealing the old oil hole in the in the timing side case might be the inner ring of the bearing loose on the shaft journal and not sealing the old oil hole in the crank. Has the outer timing cover an alloy block welded inside it to hold the oil chamber and seal for the crank is this cracked somewhere or is a weld leaking when hot. I would look very closely at the PRV thread as they have been known to leak between the inner thread into the oil relief chamber then bleed off pressure, SRM's PRV as mentioned has the first part of the thread made oversize to "bed into" the female thread in the cases, the instructions they give say that you must back and forth it into the case and there is a torque mentioned that the PRV should give as it initially screws into the cases to form a tight thread. The leak is somewhere keep looking!