Oil Pressure

Hello

I know that this has been the subject of many threads, and I’ve been searching, but can’t find the information I need to feel confident about my way forwards.

A while back, I was becoming increasingly concerned about wet sumping – the tank was emptying in a couple of days. I refurbished the oil pump, and fitted an oil pressure gauge to monitor the result of my work. Wet sumping was much improved with no appreciable drop in level over a couple of weeks, which I regarded as success.

However, oil pressure was not what I hoped to see. On start up, it is showing 60 psi, but pottering around in cooler weather drops this to around 15-20 psi and, of even more concern is that pressing on, and particularly in hot weather, this can fall even further to around 10 psi with the gauge firmly on its stop at tickover.

I’ve verified that the oil feed holes in the rocker spindles are facing outwards, and have just removed the timing cover to verify that all the seals are still sound (they were renewed when I did the pump). The only question in my mind is how I can be sure that the conical oil pump seal is actually in contact with the timing cover. There doesn’t seem to be any difficulty in pushing the timing cover right home, even without a gasket in place.

I don’t want to consider a bottom end rebuild unless it is absolutely necessary. The bike is going superbly (tempting fate here) after much recent work with no worrying noises that I can detect.

The bike is a 72 Combat, oil is Castrol XL 20w50, and the bottom end has never been touched. Sorry this is so long winded. Thanks in advance for any suggestions.

Ray

snowdr said:

There doesn’t seem to be any difficulty in pushing the timing cover right home, even without a gasket in place.

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There should be a gap when offering up the timing cover that does not close without pressure, you can add shims for going behind the seal to bring it out. The seal should have a round witness mark from the timing cover showing it has been pressed by the timing cover.

But first check the pump has the seat for the seal as it can be separated.

As kommando says
There should be a noticeable witness mark on the conical seal

I think those pressures are normal, no?

snowdr said:

On start up, it is showing 60 psi, but pottering around in cooler weather drops this to around 15-20 psi and, of even more concern is that pressing on, and particularly in hot weather, this can fall even further to around 10 psi with the gauge firmly on its stop at tickover.

Click to expand...

Seeing 60 psi on cold start up is what I would call normal, and seeing 10-15 psi hot at tick-over is also not unusual. The important part that needs to be clarified is a pressure of about 40 psi at cruising speed (~2000 rpm+) with the engine at operating temperature.

Can you verify this pressure?

60 psi on start up is just about normal, but I would be happier with 65, so, the pressure relief valve needs shimmering, me thinks.
That mod done you should see the normal pressure go up a little.
I must stress I use mutigrade oil, if I used a straight SAE 50 the pressure on start up would be higher.

Where are you tapped into the oil delivery circuit measuring pressure.?

The pressures that I quoted are at 3-4000 rpm. I haven't taken it higher when I'm only seeing 10 psi.
The take off for the oil pressure gauge is the drive side cylinder head feed.
Comments about witness marks on the conical seal are interesting, because I see no marks on it at all. I will investigate.

I am measuring oil pressure at the same location.

Incidentally, when I installed my gauge, I had NO oil pressure. I found that the oil gallery blanking plug in the timing cover was totally absent (i.e. never installed at the factory!!) Cost the original owner of the bike an engine.

I would suspect that your oil pump seal compression is in question. Once that checks out, if you are not seeing a solid pressure increase at engine speeds about 2000 RPM, my next stop would be the pressure relief valve.

If neither of those bear fruit, then I am afraid you will be going deeper into the engine (not likely, but possible).

I have a new AN pump and a new SRM blow off valve. It will hold 42 psi hot 2500 rpm . Start up blows off
less than 50. Since it will hold at least 40 even hot and slow it is fine by me.
Yes the button is clearly deformed.

You sure you have the right oil seal? The conical one is correct. There is a flat one for Mk3. If correct then
look at shimming the pressure relief valve.

FWIW, 74 Mk2 (i'm guessing factory stock pump/internals) oil, 20w50 synthetic blend. engine hot, at operating temp - steady state cruse (around 3000 rpm) - about 45 psi, idle, 1000 RPM - 20 psi

lazyeye6 said:

You sure you have the right oil seal? The conical one is correct. There is a flat one for Mk3. If correct then
look at shimming the pressure relief valve.

Click to expand...

And washer..

snowdr said:

The pressures that I quoted are at 3-4000 rpm. I haven't taken it higher when I'm only seeing 10 psi.
The take off for the oil pressure gauge is the drive side cylinder head feed.
Comments about witness marks on the conical seal are interesting, because I see no marks on it at all. I will investigate.

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EOM type plastic (top end) oil lines? Or braided stainless kit?

Yes, plastic oil lines to the cylinder head, replaced a couple of years ago.
The oil pump seal is the correct conical type. It looks absolutely as new, with no marking at all, suggesting it may not be under pressure from the timing cover. I'm hoping to spend time on it tomorrow.
Thanks for all the advice.

Are the last two posts aware that you can fit a washer between oil pump and rubber cone seal?
They are available from Norvil.

A picture would be nice

This thread got me to thinking...(which I have often found to be dangerous, confusing and or non-productive).

However...

Engine oil pressure senders/sensors are located by engine manufacturers in the main oil gallery at or immediately following the oil pump, where pressure is the highest in the system. BUT, the valve train, basically the END of the oil plumbing where pressure is lowest, is the source point for the typical Norton oil pressure gauge setup.

Oil pressure senders located anywhere other than the main oil gallery are not reading engine oil pressure as it is commonly understood/calibrated. The standard "10 PSI per 1000 RPM" applies at the oil pump/in the main gallery, not at the valve train.

What I'm suggesting is that readings on a pressure gauge plumbed into the Norton head/valve train is not 'accurate' oil pressure and it may cause consternation over perceived low oil pressure where no such problem exists.

The pressure reading is equal within the pressure zone or inside of the tight clearance escape routes whether these be the big ends or the rocker shafts.

kommando said:

The pressure reading is equal within the pressure zone or inside of the tight clearance escape routes whether these be the big ends or the rocker shafts.

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IMO pressure is also dependent to some extent on how worn your big end shells are, if you see what I mean.