Author Topic: Disappearing Oil Pressure!  (Read 2586 times)

Offline alanp

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Disappearing Oil Pressure!
« on: 03.11. 2011 10:44 »
Ok, have a think about this.
Engine - SRM build with SRM oil pump, Wiseco pistons, 3000miles, oil pressure gauge, return oil filter, oil cooler, 20W50 Silkolene Comp 4 oil, runs well.
Problem - A week or so back I had just got about a 1/4 mile from home when I noticed that the oil pressure, which is normally about 65/70psi cold, was falling rapidly to the 'oh my god' level, i.e. maybe 5/10psi. If I let it tick over it comes back up again which led me to think that the pump was being starved of oil at its inlet. Normally, when fully hot during a high speed run , it would run at 25/30psi and hold 65/70psi for maybe 10 miles or so depending on how fast I was going and ambient temp.
Action so far -
Oil level in tank - ok
There is no valve in the oil line to have left closed (before someone suggests I open the valve)
Drained oil from tank
Checked the gauze filter in the tank - ok
Removed the oil line to the engine and confirmed it is clear and not blocked.
Blew through the fixed oil line inside the tank - ok
Removed the timing side cover
Removed the SRM pump
Dismantled the SRM pump and all inside is in mint condition.
Checked oil pump drive - ok
Blew through the oilway from the outside of the engine casing to the pump inlet port - ok
Passed a wire into the inlet oil way until I could see its end at the oil pump inlet port - ok
Removed and dismantled the SRM PRV - ok
Reassembled it all and test rode it again - same result !!!!
Fitted a standard PRV in place of the SRM PRV and same result only 50psi with this PRV.
Refitted the SRM PRV.
Any suggestions gentlemen?  

Member of the 'Last of the Summer Wine Club - Jennycliff'.

Online bsa-bill

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Re: Disappearing Oil Pressure!
« Reply #1 on: 03.11. 2011 11:08 »
Pretty comprehensive test of everything Alan - bar the pressure gauge! - just a thought

Wayhay
Quote
bar the pressure gauge!
just reread that, there's a pun in there, unintended
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline kiwipom

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Re: Disappearing Oil Pressure!
« Reply #2 on: 03.11. 2011 18:13 »
hi guys,sounds like a faulty pressure gauge to me Alan,cheers, bob
A10.G.Flash(cafe racer)Honda 250 vtr. Yamaha Virago XV920.

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Offline A10Boy

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Re: Disappearing Oil Pressure!
« Reply #3 on: 09.11. 2011 10:15 »
Al
A few questions.

You say SRM build, is that with an end feed conversion or std bush? Did SRM assemble the engine, I'm assuming yes.

Have you done 3000 miles since the build without problem?

Where in the system is the oil cooler?

Are all the pipes new? I've seen pipes colapse internally when hot and close up.

Did you do anything at all to the bike prior to noticing this, like change oil?

Have you tried disconnecting the filter and cooler so you just have a basic oil supply to the engine? [I think I would try that]

Cheers

Regards

Andy

1958 Super Rocket
Plus
1974 Kawasaki Z1a
Yam XJR 1300

Offline alanp

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Re: Disappearing Oil Pressure!
« Reply #4 on: 09.11. 2011 12:01 »
I owe you chaps an update.
Yes, a10boy, it's fully SRM and had been going well and the filter and cooler are on the return side of the system.
After the pretty comprehensive check of pipes, pump and oilways and refitting the SRM PRV I have had to wait for a dry'ish spell to give it a run. I managed a short run of a few miles and the oil pressure seems stable. If (still an 'if') it is now ok I'm baffled. Before this run I took the plugs out and kicked it over until I saw around 25psi on the gauge before starting it up to make sure that I had primed the oil system since the pressure tapping is after the pump. But, then again, the gauge showed normal pressure before it dropped on the first occurence run so I had assumed it was primed.
The problem of course started after I had changed the pipe from the oil tank to the engine and, yes, you need to get oil primed thru' to the PRV before starting after this but I didn't. However, don't hang me yet... that doesn't explain how, after the pressure had dropped on the run, that it came back up again at tickover when I stopped and dropped again right after I restarted. It all seemed like oil starvation to the pump to me which is why I concentrated on the oil feed to the pump.
So, did I get an airlock in the line to the pressure gauge? I have some difficulty in relating this to what happened but I don't really know.
I need to give it a longer run but I have been preoccupied with dealing with a carburation problem on my Honda XR 250. The weather is promised to clear up in a few days so I'll run the BSA again and let you know how it turns out. I will be peering nervously at the pressure gauge though I assure you.
Cheers
Alan
Member of the 'Last of the Summer Wine Club - Jennycliff'.

Offline A10Boy

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Re: Disappearing Oil Pressure!
« Reply #5 on: 09.11. 2011 13:42 »
Yes, I thought it could be related, do you need to "bleed" the gauge pipe assuming its a pipe not a sender?
Regards

Andy

1958 Super Rocket
Plus
1974 Kawasaki Z1a
Yam XJR 1300

Online RichardL

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Re: Disappearing Oil Pressure!
« Reply #6 on: 09.11. 2011 14:31 »
I think it is correct to say that the return being faster than the supply puts bubbles in the oil. Bubbles at the top of the oil tank when viewing the return seem to verify this. I have wondered if the little hole in the left connecting rod was not actually put there to prevent bubbles at the end of the sludge trap from forming an air chamber that dams oil flow.  Back to the point,  bubbly oil won't show the same pressure on the guage as viscous liquid oil.  It would seem bubbles are no(t present in start-up, early-run oil,  but build up over time.

Richard L.

P. S.  Notice my many attempts to avoid sounding sure of myself.  That's for a reason
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online bsa-bill

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Re: Disappearing Oil Pressure!
« Reply #7 on: 09.11. 2011 15:51 »
Hi Richard
Bubbles are indeed a result of the return have more flow than the feed, that is once the pump has cleared any backlog of oil in the sump.
At start up there will nearly always be some oil in the sump - drain down from after the engine stops - any wet sumping that may have occurred.
so at start up there may be no bubbles for a little while, and I'm not sure but perhaps this can happen after returning to idle
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online RichardL

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Re: Disappearing Oil Pressure!
« Reply #8 on: 09.11. 2011 16:32 »
Bill,

I think even if the sump were dry at startup it would take some time to churn bubbles into the oil that might build up in a dead-end passage like a pressure guage.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online bsa-bill

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Re: Disappearing Oil Pressure!
« Reply #9 on: 09.11. 2011 17:43 »
Richard your into what for me is one of life's great mysteries, working on a farm most of my life I was always amazed at how oil filled a hydraulic ram so quickly and completely even after it had been removed or replaced, I'm talking about single acting rams where oil is fed into one end (no breather or means to bleed them ), mechanics I've asked just say " well it sorts itself out with the pressure" and it seems to be true so possibly it's the same for a pressure gauge, a bit of air in there would give a low reading and in a short time get squeezed out - I'm no hydraulic engineer though.

As a paramedic said to a man giving artificial respiration to a half drowned man on the side of a pond " you'll get on faster if you pull his ass out of the water" *whistle*
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline trevinoz

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Re: Disappearing Oil Pressure!
« Reply #10 on: 09.11. 2011 19:12 »
Could I say that this is the reason oil pressure gauges were discontinued from being fitted to bikes?

  Trev.

Online chaterlea25

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Re: Disappearing Oil Pressure!
« Reply #11 on: 09.11. 2011 21:35 »
Hi All,
oil or air the gauge doesnt care  *ex* *ex* *ex* *ex*
the same gauge works for all media, if it didnt it would mean hundreds of different gauges would be required   *eek*

Alan, the BSA engine should self prime, Your problem started with changing the feed pipe, maybe there was something inside the length of pipe??, probably lost when you drained blew everything out
when you say the gauge tapping is after the pump,I'm assuming its before the PRV?

The oil tank acts as a settling vessel the air in the oil should rise away from the feed supply at the bottom,

Cheers
John O R

1961 Super Rocket
1963 RGS (ongoing)

Online RichardL

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Re: Disappearing Oil Pressure!
« Reply #12 on: 10.11. 2011 00:22 »
Darn it!  The one sentence I didn't equivocate and I was wrong.  Apparently.  So,  John,  the mix of densities (it is densities,  right?) between liquid oil and bubbly oil makes no difference on the pressure guage's diaphram or tube or whatever? Answering my own question, I think, the air pressue inside the bubbles is the same as the oil pressure.

Give me a break,  the degree is in electrical.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

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Re: Disappearing Oil Pressure!
« Reply #13 on: 10.11. 2011 00:42 »
Hi Richard,
Dont beat yourself up over it  *ex*  *smile*

Regards
John O R
1961 Super Rocket
1963 RGS (ongoing)

Online bsa-bill

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Re: Disappearing Oil Pressure!
« Reply #14 on: 10.11. 2011 09:40 »
Quote
oil or air the gauge doesn't care

I can see that John but air is compressible oil is not, if there was sufficient air  would it not make some difference to the gauges reading
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco