Lotus Elan

Too much oil pressure?

PostPost by: rgh0 » Sun Mar 22, 2020 4:24 am

Davidb wrote:Thank you Rohan!

From Keith Dixon's paper:
"As a rule of thumb, it is reasonable to allow for a pressure drop of 10% for each right angle change of direction {of oil flow} ."
That is what I was trying to overcome/avoid.

So Rohan, it does mean that the flow is increased-which is a good thing-but pressure would be unchanged?

I am still trying to understand why I am getting 60psi oil pressure with the new standard pump and was getting 55 psi with the old, standard pump (measured with a stand-alone gauge)?


Only 3 possible causes I think assuming your pressure measurements are accurate which they seem to be if two independent gauges give similar readings

1. Both are actually high pressure pumps with an approx 60 psi relief valve
2. If both pumps discharge back to the sump rather than recycle to the suction then maybe a blockage in the discharge line to sump or if recycle to the pump suction then an obstacle to that.
3. The relief valve on both the pumps is sticking and not fully opening

Even at high revs with a stone cold engine and oil the relief valve should limit the pump discharge pressure to near 40 Psi

cheers
Rohan
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PostPost by: nmauduit » Sun Mar 22, 2020 12:38 pm

Davidb wrote:Thank you Rohan!
So Rohan, it does mean that the flow is increased-which is a good thing-but pressure would be unchanged?


not to overstep on Rohan's feet, to me reducing causes of pressure loss (taking hard corners, giong around burrs ... etc ) other than the oil is useful (bearings) is a good thing, though how to achieve that significantly given the oil circuit being mostly cast and buried may not be easy. For quantitative estimates, looking into reynolds numbers of your favorite oil would be a start, won't get started myself even if I like the idea or deburring wherever practical.
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PostPost by: Davidb » Fri May 15, 2020 2:45 am

Update.
So today I finally got back to working on the Elan engine. When Covid19 struck and all events were cancelled I simply left the car and worked on other things-repainting the house, gardening etc...(Yuk!)

Here is what I found.
I removed the new oil pump and thanks to tips on this forum it was easy. I supported the engine, removed the two bolts that hold the r/h engine mount to the chassis, jacked up the engine and slid out the oil pump. ( I did remove the end plate but found it was unnecessary because the pump came out/in anyway.
I examined the pump and compared it to the old pump. Finally I realised that the oil pressure relief valve on the old pump was stuck open! I had not noticed this before since I found the oil pick up pipe fractured and concluded that was my only problem.
P1090132.JPG and


So now I examined the new pump to find the cause of the high oil pressure. Was it a HP pump in a STD box or what? What I found was that the oil pressure relief valve spring had an arc to it-unlike the original pump where the spring was straight. I examined it closely and finally realised that the spring was installed incorrectly. It uses a retaining plate-which is shaped like a washer but the centre hole is actually punched out as a protrusion that locates the spring. The spring had been installed incorrectly and instead of sitting with the spring surrounding the protrusion it was sitting on the edge of the protrusion thereby reducing by an eighth of an inch the fitted length of the spring and increasing pressure. I jammed a Philips screwdriver down the hole in the retaining washer, there was a "twang" and the spring was in the right place. Here is how the spring would have looked out of the pump:

So cleaned and refitted the new pump and spun the engine over on the starter-with plugs out and the carbs still unfitted and I get 45lbs oil pressure! I also found that the threaded section that the oil filter threads onto was loose in the oil pump.

I think the lesson here is to check these pumps thoroughly before fitting!
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P1090135.JPG and
Last edited by Davidb on Sat May 16, 2020 3:40 pm, edited 3 times in total.
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PostPost by: StressCraxx » Fri May 15, 2020 3:26 am

Great catch. The devil is in the details..

Enjoy your Elan when they finally allow you to "Release the hounds!"

Regards,
Dan

Davidb wrote:Update.
So today I finally got back to working on the Elan engine. When Covid19 struck and all events were cancelled I simply left the car and worked on other things-repainting the house, gardening etc...(Yuk!)

Here is what I found.
I removed the new oil pump and thanks to tips on this forum it was easy. I supported the engine, removed the two bolts that hold the r/h engine mount to the chassis, jacked up the engine and slid out the oil pump. ( I did remove the end plate but found it was unnecessary because the pump came out/in anyway.
I examined the pump and compared it to the old pump. Finally I realised that the oil pressure relief valve on the old pump was stuck open! I had not noticed this before since I found the oil pick up pipe fractured and concluded that was my only problem.
P1090132.JPG


So now I examined the new pump to find the cause of the high oil pressure. Was it a HP pump in a STD box or what? What I found was that the oil pressure relief valve spring had an arc to it-unlike the original pump where the spring was straight. I examined it closely and finally realised that the spring was installed incorrectly. It uses a retaining plate-which is shaped like a washer but the centre hole is actually punched out as a protrusion that locates the spring. The spring had been installed incorrectly and instead of sitting with the spring surrounding the protrusion it was sitting on the edge of the protrusion thereby reducing by an eighth of an inch the fitted length of the spring and increasing pressure. I jammed a Philips screwdriver down the hole in the retaining washer, there was a "twang" and the spring was in the right place. Here is how the spring would have looked out of the pump:
P1090132.JPG


So cleaned and refitted the new pump and spun the engine over on the starter-with plugs out and the carbs still unfitted and I get 45lbs oil pressure! I also found that the threaded section that the oil filter threads onto was loose in the oil pump.

I think the lesson here is to check these pumps thoroughly before fitting!

(I dunno why there are two copies of the oil pressure relief valve photo...)
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PostPost by: 2cams70 » Fri May 15, 2020 4:29 am

Thanks for closing the topic. That's very useful information
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PostPost by: vstibbard » Fri May 15, 2020 6:25 am

Well done.

Vaughan
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PostPost by: alan.barker » Fri May 15, 2020 8:19 am

Well done that man and good info.
Was the Oil pump made in Chintok land 8) 8)
Alan
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