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Hole in oil pressure relief valve

fredeuce
Posts: 76
Joined: Mon Feb 29, 2016 10:56 am
Location: South Australia

Re: Hole in oil pressure relief valve

Post by fredeuce »

I went through this exercise recently when rebuilding my engine. Having trained as a diesel mechanic in years past and having rebuilt many engine ensuring proper oil pump functioning was essential. That practice meant performing on bench testing of the pump. This simply involved holding the pump suitably such as a vice and attaching a oil pressure gauge and turning the pump with the aid of a brace or similar to rotate the pump.
Those tests on those pumps would always generate pressure and allow the relief valve to function.

Performing a similar on bench test with the Daimler pump this resulted in no oil pressure being generated on the gauge as it was relieved entirely through the drilling in the relief valve plunger. I was somewhat alarmed by the amount of flow that was diverted by the drilling. It is fair to say having rebuilt a variety of engines over the years this feature on the Daimler is somewhat unique. For me I deemed it unnecessary and filled the hole with silver solder. Further tests resulted 40 psi immediately . I conducted some further tests with packing behind the spring to raise the opening point of the relief valve. I raised it to around the 50 psi mark.

Another observation I made was that as I have a remote mounted oil filter my practice has been to crank the engine to generate oil pressure before firing. This meant cranking for a considerable period before oil pressure was generated. I concluded that there is a measure of drain back created by the drilling. This has now been eliminated.

Ian Slade
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Posts: 791
Joined: Sat Feb 13, 2016 9:54 am
Location: Sevilla Spain

Re: Hole in oil pressure relief valve

Post by Ian Slade »

As I understand the relief is not back to the sump but by passes the filter, it was known since the 50's or even earlier ( wasn't old enough before then to understand the intricacies of petrol ICE) that from new oil the bypass was 70% increasing as the filter became more clogged. Vigorously turning the pump by hand would not be a reasonable test of a 1950's designed engine oil pump, diverting that pressure to the filter in those days would collapse the filter and definitely cause excessive wear to the pump. Diesel engines not derived from petrol engines are a different animal and due to the very high compression ratio need a somewhat different arrangement. 50psi in the standard filter would blow the oil seal at the bowl to casing joint, just look at the loading on the filter bowl bolt, about 350lbs
Owner since the 70's, Genghis is slightly to my left.

Tennant
Posts: 69
Joined: Sun Jan 20, 2019 7:13 pm
Location: Herne, Germany

Re: Hole in oil pressure relief valve

Post by Tennant »

Ian,
The relief valve dumps the excess oil directly back into the sump through holes in the pump side.

Fredeuce,
I am with you on this because:
1 - I have never seen such a hole .
2 - I have not been able to find any reason why it is there.
3 - When really hot, the oil is like water, and the 400 RPM tickover would surely pump oil but you need every PSI you can get on a older engine.

Perhaps I am wrong. We shall see.

Barry

fredeuce
Posts: 76
Joined: Mon Feb 29, 2016 10:56 am
Location: South Australia

Re: Hole in oil pressure relief valve

Post by fredeuce »

Here is a picture of my pump. The exit port for the relief valve exits to the sump . The cap that holds the relief valve spring is also vented to the sump.

The standard oil filter housing has its own separate relief valve to guard against filter blockage. That is not related to this discussion.

The bench testing of oil pumps in the manner described was a widely used practice in the GM dealership I learned my trade in across the board of both petrol and diesel engines to ensure essential functioning of the pump before engine assembly. A perfectly valid and necessary test to be done before assembly. Clearly once and engine is assembled a master oil pressure gauge needs to be fitted to ascertain oil pressure when running.

Image

Tennant
Posts: 69
Joined: Sun Jan 20, 2019 7:13 pm
Location: Herne, Germany

Re: Hole in oil pressure relief valve

Post by Tennant »

Freduce,

Mine looks the same.

Instead of welding the hole in the piston, I have sealed the hole in the cap at the end. It will have the same effect I suppose.

Barry

fredeuce
Posts: 76
Joined: Mon Feb 29, 2016 10:56 am
Location: South Australia

Re: Hole in oil pressure relief valve

Post by fredeuce »

Barry,
By sealing the hole in the cap holding spring and plunger in place I believe you are potentially creating an hydraulic lock where the space in around the spring would fill up and prevent the plunger from moving and effectively jamming the relief valve entirely. That is not a desirable outcome . Filling the hole in the plunger is what is needed here.

Cheers, Fred

Tennant
Posts: 69
Joined: Sun Jan 20, 2019 7:13 pm
Location: Herne, Germany

Re: Hole in oil pressure relief valve

Post by Tennant »

Hi Fred,

Thanks. That was just what I was looking for. Logical when I think of it. If the pressure front and back of the plunger are the same then it cannot move.

Thanks for stopping me blowing up!!

Filling the hole it is then.

Barry

Chris_R
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Location: Twickenham

Re: Hole in oil pressure relief valve

Post by Chris_R »

Tennant wrote: Thu Apr 01, 2021 12:55 pm 3 - When really hot, the oil is like water, and the 400 RPM tickover would surely pump oil but you need every PSI you can get on a older engine.
Barry, I will correct you on this point. When really hot, oil is not like water. When really hot, oil is just like hot oil. Quite different. If you study these things you will see in the technical specifications for oil a viscosity value. This is a measure of the thickness of the liquid which varies according to temperature. When cold it is quite thick, when hot it is thinner. At 100c an SAE40 oil will have a value of between 12.5 and 16.3 centi-Stokes. An SAE50 oil will have a value between 16.3 and 21.9 centi-Stokes. Water has a value of 1. This is why you can't use water to lubricate your engine!

Tennant
Posts: 69
Joined: Sun Jan 20, 2019 7:13 pm
Location: Herne, Germany

Re: Hole in oil pressure relief valve

Post by Tennant »

Thank you Chris. I was only speaking metaphorically, I have vague memories of making the SAE cup test in Physics during my studies (55 years ago!).

Perhaps and interesting point. I closed the hole yesterday and re fitted it. It does not have a sealing surface as such, I am not sure how to describe. It is a barrel piston that slides inside the cylinder and seals off the pump drain holes on the side. It does not seal very well and you can blow air past it. So when a little worn, the hole is probably only a half of the flow past the valve.
I will be ordering a new piston in hope that it will be a better fit.

An interesting part of the engine.

Thanks for your input.

Barry

Christopher Storey
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Posts: 404
Joined: Wed Mar 16, 2016 6:40 pm
Location: Cheshire

Re: Hole in oil pressure relief valve

Post by Christopher Storey »

Ian Slade wrote: Thu Apr 01, 2021 12:03 pm 50psi in the standard filter would blow the oil seal at the bowl to casing joint, just look at the loading on the filter bowl bolt, about 350lbs
Some kind of error here, isn't there ? 35lb/ft I can see, but I have never ever come across a setting of 350 lb/ft

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