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SP250 V8 oil pressure

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heh101353
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SP250 V8 oil pressure

Post by heh101353 »

Hi everybody

I'm new to this forum and very much a newbie to the world of classic cars. Some forty years back I was heavly involved in restoring BMW motorcycles and I guess I still might be able to dismantle and put together again a BMW R25/R26 „blindfolded“.
I bought a Daimler SP250 (Chassis 101353, June 1960) from a dealer here in Switzerland, who did import the car in 2011 . It was stored until I bought it. The car needed a bit of love to get the blessings from the swiss authorites and by June 2016 it was back on the road. Everything looks fine and it is a very enjoyable experience to drive the car. But there is something that bothers me albeit the workshop guys keep telling me there's no reason for concern. The first 5000 miles the reading of the oil pressure gauge was always at 15 psi. at tick over and around 45 psi. above tick over. Suddenly, without apparent reason the gauge started to read 30 psi. at tick over and close to 60 psi. above. Now at some 3000 miles plus the gauge will stay at close to 60 psi. whatever the RPMs. Sometimes but very rarely, at tick over the gauge drops to 30 psi or even below but will be back at close to 60 as soon as the revs go up again. (The temperature of the engine oil does not matter at all). By the way the engine stems from a V8 saloon.
My first concern lies with the oil pump. I guess it's always working at it's limits.
Other probable adverse affects on: gaskets, bearings, ... ??
Cause of the problem: oil pressure relieve valve not working, blocked lubrication channel, ??
What readings do others get? What would be „ideal“?
Sorry for being a bit long winded and please excuse my faulty English.
Any thoughts are most appreciated.
Thanks a lot
Hans

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John-B
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Re: SP250 V8 oil pressure

Post by John-B »

This topic may help as it mentions limitation of oil flow and high pressure and the pressure relief valve.

viewtopic.php?f=34&t=2720

Phillmore
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Re: SP250 V8 oil pressure

Post by Phillmore »

It might be worth checking the gauge and sender and their wiring and connections and oil filter before delving deeper into pumps and blockages.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

Ian Slade
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Re: SP250 V8 oil pressure

Post by Ian Slade »

With a V8 250 engine in an SP one first must check whether there is a sender or a Bourdon tube pressure gauge, there is no doubt that a car that has been stored and then recomissioned with just a service may well have some problems unless some form of engine cleaning has been carried out. Engines left especially if containing old oil can have glutinous deposits in any of the oil ways, sometimes this can be a hard coating inside the engine and will wash away into the sump, the worst case can be a blocking of the scavenge filter in the sump, this can have the effect of varying oil pressure as the scavenge filter drops and collects the gunge during periods of use and storage. I would drop the sump and have a look, I had this problem many years ago, though not on a Daimler engine which required new bearings though fortunately not a regrind.
Owner since the 70's, Genghis is slightly to my left.

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heh101353
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Re: SP250 V8 oil pressure

Post by heh101353 »

Thanks a lot for your kind replies.
The gauge is a sender type. And there was no change to any component involved.
I'm about to move to another workshop. The current one is not up to my expectations. Not that my expectations are outrageous, but quite a few tasks they tackled had to be redone until the issue at hand was gone for good. I'm sick of it ...
Monday next week I will see a guy with 40+ years of experience with classic-cars (never worked on modern cars) and the best of it, he has worked on several Darts and has even two customers with SP250s on a regular basis. Will see what comes out of it.
Anyway thanks again!
Hans

By the way, this is mine ...
Image
:o owner since 2015 :mrgreen:
https://www.wyhe.ch/

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RadfordJim
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Re: SP250 V8 oil pressure

Post by RadfordJim »

Hello Hans and welcome to the Forum. My car is chassis 101472 manufactured in July 1960 but held back or returned to the factory for the B spec upgrades. It was registered on 1 March 1961. I have the original engine which has just been rebuilt at 98000 miles and oil pressure via the Bourdon tube shows 50 psi at tickover and 55 psi when running.
Lets hope your new workshop man can sort the problem and please post to let us know.
Your car looks very nice, is it A or B spec?
This is mine which looks similar to yours without bumpers
MillbrookDart.jpg
Jim in Coventry - Home of the Daimler

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wally999999
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Re: SP250 V8 oil pressure

Post by wally999999 »

I'd definitely fit a temporary mechanical gauge and check the pressure before doing anything else. It may even be worth substituting a new (or borrowed) gauge of the type you already have. From what you've described by far the most likely cause is an issue with the gauge / sender / wiring.

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heh101353
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Re: SP250 V8 oil pressure

Post by heh101353 »

First of all many thanks for the warm welcome Jim.
Mine is chassis 101353, 24. June 1960. Pretty much original. Well, on images cars almost always look good ...
But looking real close, it has quite a few chips and a bit of crazing around the edges. But nothing serious.

@Wally
Not a bad idea. I will take it to the meeting with the guy at the "new" workshop next week.

Thanks again for the kind feedback
Hans

Chris_R
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Re: SP250 V8 oil pressure

Post by Chris_R »

Perhaps a little bit of technical explanation may help. The pressure reading that you are seeing is the resistance to the flow of oil in the engine, mostly this comes from the bearings on the crankshaft. The faster the engine is turning the greater the flow of oil in the engine however there is only a fixed amount of space for the oil to flow through and so you have more oil trying to get through and so the pressure reading increases which is the back pressure to that increased flow. The oil pump will pump far more oil than the engine can use and the excess spills back via the oil pressure relief valve. The pressure relief valve operates to regulate the pressure in the system. Until the pump is delivering more oil and the back pressure reaches a certain point the valve is closed. Once the volume of oil exceeds the capability of the engine to use it by a certain amount the relief valve will open. 15psi at idle is OK, as is 45psi when running. If it doesn't go above 45 psi then in all probability the relief valve was opening and excess oil from the pump was spilling back.
Most observations on a change of pressure involve where the observed pressure goes down which will happen if the crankshaft gets worn and the oil can flow more easily out of the bearings. It is unusual to see an increased pressure reading causing concern but any change in behaviour should be investigated.
This could be a sender or gauge problem as has already been suggested. Other possibilities are a thicker oil following an oil change as a thicker oil is more reluctant to flow and therefore produces a higher resistance and a higher pressure reading. Also it could be that the workshop has "fiddled" with the pressure relief valve to stay closed longer. Finally there could be a blockage somewhere constricting the flow and this would also result in a higher pressure reading.
The important thing is that you have noticed it and will ask your new workshop to check it out.
Hope this helps.

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wally999999
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Re: SP250 V8 oil pressure

Post by wally999999 »

As a slight aside - I've rebuilt my engine twice over the last 40 years (doing all the work myself). I happened to speak to Russ Carpenter (of Daimler dragster fame) around the time of the most recent rebuild. He suggested putting a 3/8" spacer behind the oil pressure relief valve spring to increase the default pressure slightly. So I made up a simple spacer from a piece of brass rod and this has been in my SP ever since. All has been fine since (10 years) but there again, it was fine before too. The second rebuild was triggered by a cracked block, rather than any problem relating to bearing wear.

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