oil pressure relief valve (in block)

[cbudden]

Hello Everyone,

Looking for advice on the following problem;

I am turning over my newly rebuilt engine and can only obtain oil pressure if I (temporarily) completely block off the pressure relief valve in the block. When I originally tried turning over the engine (with the front crankcase cover off, I could see that within a few turns of the engine it was dumping oil from the relief ports of the valve. As a test I rigged up a dome nut on a spindle and tightened it in place with the cap screw on the block. With this in place I get oil pressure of just over 40PSI (on a new temporary gauge) whilst the engine cranks over - does this seem reasonable?

My thinking was that if a dome nut wedged in place restores pressure, then the problem lies with either the spring or the little piston....... I found a great photograph and description from Karl giving the spring dimensions and the pressures. I measured my spring and it does not match the dimensions given by Karl and feels very 'spongy'. I spoke with Lee Springs and they provided a replacement spring which they claim should match the compression requirements given on Karl's picture.

I have fitted the replacement spring but unfortunately I still do not get oil pressure on cranking the engine over..... this leads me to think that the little piston must be the problem. I attach a picture of it. I don't think it looks too poor but would welcome any comments. Are replacement or substitute pistons available? Can it be modified or repaired in any way?

I also attach a (not very good) picture taken of the internals of the relief valve - I assume that the 'shoulders' of the piston seat against the face just beyond the bypass outlets?

Grateful for any advice that will help me move towards a first engine start.

Regards
Chris

[Kari]

Chris,

Fine you get oil pressure by cranking the engine. You didn’t state if this was done by starter motor or crank handle. But to have proper oil pressure, the engine must be running, a constant flow will be needed.

As you look at the piston you'll find a small bore in the centre. This is where you will see oil escaping. This is standard and IMHO the small bore serves to speed up the oil pressure when starting the engine. When the engine is not running, the (hot) oil will drain all the way to the sump and leave an air pocket in the oil ways. On the next start the small bore will allow the air to escape and the oil from the pump will flow quickly to the crankshaft bearings and further up.

The regulating valve is set to 3 bar (about 45 psi) and protects the oil ways, gaskets and the instrument. This is when the oil is cold. When the oil is getting hot, the regulating valve will mostly be closed, especially on low and midrange revs.

So, I suggest you assemble the engine and run it. Then you'll see where the oil pressure is going to, and you can adjust the spring in the relieve valve until it's opening when the pressure raises above the "normale" range of the pressure gauge. Please make sure the seat on the valve and in the block is clean, no corrosion, it's 45° in case you have to restore it.

I suggest, using a good grade engine oil which is designed for vintage car engines.

Karl

 

[Kari]

Looking again at the picture "oil way", I think I have mistaken it for the bore in the cylinder block. I think it's the inside of the piston. Therefore, disregard my added graphics.

Attached a picture of the bore in the block. The seat is just partially visible.

Karl

[cbudden]

Hi Karl,

As always many thanks for your reply. I was not very clear in my original post regarding cranking the engine over - this is being done on the starter motor (WOSP hi torque replacement unit) and I have no plugs in.

You were correct the first time - my poor picture is of the bore in the block, not the internals of the piston.

I think I have been completely misunderstanding how the valve works...... if I interpret your reply correctly the leading edge of the front of the small piston seats onto the very edge of the smaller diameter hole (approx 35mm into the block)? I was thinking it was the wider section behind the drilled holes that provided the seal.

If this is the case then presumably some oil is bled away even when the valve is in the closed position?

Would you expect any oil pressure to register on turning over the engine, for 20 seconds or so, on the starter motor? I am using a new, non-Lancia oil pressure gauge for this exercise that indicates in PSI/Bar. What are the approximate values in Bar or PSI for the range indicated as 'Normale' on the original gauge?

I like the idea of actually running the engine (the ultimate goal) but am paranoid about a lack of oil pressure/lubrication in a 'new' engine.

Best Regards
Chris

[Kari]

Chris,
You are right in your assumption that a small amount of oil is bled away when the regulating valve is closed.

When my car has been standing for more than 4 -5 weeks, I turn it on the starter motor, plugs removed, for half a minute or so, until pressure is raising on the instrument. So, it is nicely pre oiled.
You have nothing to worry when starting the motor, give it some time to build up pressure. You can always switch off. If you run it on the starter motor, you can check, with the valve cover removed, if oil is seeping from the rocker shaft and the chain tensioner.

The oil pressure is not critical, as long as there is oil transported to the crank shaft bearings, it's fine. While driving, within the "normal" range is fine, idling on a hot engine can be quite low, almost near zero. This is depending of the general condition of the engine (clearances) and the oil viscosity.

Attached the values of the oil pressure instrument of my car. We have to keep in mind that those instruments are around 90 years old and might not be very accurate. I think the "normal" range would be between 1.5 to 3 bars. If you adjust the spring tension in the regulating valve, just make sure that the instrument does not go to to the upper end of scale on cold oil.

Cheers

Karl

[cbudden]

Good afternoon All,

Just to close this thread, I can report that with Karl's advice and encouragement I took the big step of actually trying a first start my re-built engine and monitoring for oil pressure.......it worked! The engine started on the first turn of the key (despite having fitted a non-standard carburettor) and oil pressure climbed rapidly (within seconds) on engine ignition. At a fast idle, on a cold engine with 20W mono grade oil I was seeing a steady 2Bar (approx) rising to 3-3.5 Bar on revving.

I guess that previously when only turning over on the starter motor there is insufficient flow (due to very low engine revs) to register oil pressure at the cylinder head as the oil takes the path of least resistance and diverts out through the piston in the relief valve?

Many thanks for all your replies and encouragement, I can now move on to re-wiring!!

Regards
Chris

[Kari]

Very good, your engine is running. As spring is on the doorstep and summer will follow, a 20 grade oil is on the thin side. I recommend a 30 grade oil. You will see when you have hot oil after driving the car for half an hour or so.
Best wishes
Kari