Javelin engine oil pressure

[Moises]

I'm having problems with the engine oil pressure on my Javelin. Can anyone help me? When I start with the engine cold the pressure is 50 psi at 900 rpm, and it peaks at 65 psi at 3,000 rpm. As the engine warms up, the pressure drops and when it reaches the normal temperature of 75ºC, the pressure is 7 psi at 900 rpm. and it reaches 28 psi. from 3,000 rpm. The oil used is Castrol Classic 20W-50 Can this loss of hot pressure be caused by excessive clearance in the camshaft? I will appreciate your comments. Thank you

[JUP]

I would start by checking the oil pressure relief value
If you take the sump off you can get access to it
I have just had the same problem

[David Morris]

Hi Moises,

Very good to hear from you again

Yes, your oil pressure is too low but the oil you are using is fine.

I would expect the average Javelin to read about 70 psi on start up, 60 psi when running and around 50 psi when idling and warm.

There could be quite a few reasons for your low oil pressure, the top of the list being worn bearings, but you would hear this from rattling and thumping sounds from the engine. I don't think worn camshaft journals would be the cause. My best advice is, like JUP, that your oil pressure relief valve on the oil pump is set too low. There are two types of oil pump, the earlier one where the relief valve is non-adjustable and the later one, known as a Mk.4, which has an adjustable release valve. You can only really tell which type by dropping the oil sump. The earlier pumps have a roll pin holding the end of the oil relief spring in place, whereas the later pumps, which are much more solid looking, have an adjustable screw to set the release pressure on the valve, locked in place with a locknut.

I suggest you drop the oil pan and check. This also allows you to see the condition of the gauze over the oil pump pickup, which might be another cause if it is blocked? I believe you can swap a later pump for an earlier one, but John Airey could probably advise as the oil pipes from the pump up to the filter, which are behind the front timing cover, are larger on the later pump and there may be some engineering to make them fit an earlier engine.

If you need to reset the relief valve pressure, this really needs a test rig, which several members in the UK have made up, with many using an electric drill. Without a test rig, I would suggest you tighten the adjusting screw by, say, half a turn and see how much this increases the oil pressure. Perhaps a member with a test rig can advise how much half a turn increases the running pressure?

I do hope you can discover the cause. In a odd way, it's unfortunate that your later Javelin has an oil gauge! The earlier ones just had a oil light, and if this stayed 'off' when you were running, you never had to worry about the actual pressure!

All the best,

David

[Moises]

Thank you very much for your comments. Is there any explanation for the fact that the oil pump relief valve discharges at 60 psi when cold and at 28 psi when hot?

[David Morris]

Hi Moises,

That's a very good point which I should have considered! As you said, the oil pressure at 900rpm falls from 50psi when cold to 7psi when warm. So, the difference cannot really be attributed to the oil pressure relief valve in the pump! There must be something else affecting this drop in pressure. I can only guess that the warming of the engine is allowing the slightly thinner oil to escape from the bearings, or from another outlet?

I know you asked about the camshaft bearings, but if these were badly worn I would think you would be hearing more noise from the camshaft, as the engine warms up? You mention taking the engine up to 3000rpm. How does she sound at that speed? If there was excessive bearing wear, I reckon you would hear a lot more general engine 'clatter' with only 7psi? Main bearing wear sounds like a deep rumble and big end wear sounds lighter, with rythmic tapping sounds.

Sometimes, placing a long steel rod against various parts of the crankcase and the other end of the rod against your ear helps to locate the source of sounds?

It's a bit of a long shot, but is the oil bypass flexible pipe wrapping around the oil filter old and made of rubber? Might that be affecting the oil flow when the oil is hot? I know that rubber brake hoses can get completely blocked internally when old and perished.

Let's hope other members can suggest other causes?

Best regards,

David

[Keith Clements]

Amy's Javelin has had very much the same as Moises' oil pressure and has run for 10 years like that, and when the engine was stripped last year to change the piston rings the main and big ends were fine after being checked with plastigauge.

Yes you could loose oil pressure through the camshaft ( you can read on JT how I found that out on JT, but it was very messy). Also any other point such as filter housing gasket or block joint faces can loose oil.

Of course the 60 psi when cold may not be regulated by the oil pressure relief valve but simply the flow through the engine. One cause could be that the oil pump is not able to generate 60 psi with hot oil, so perhaps your oil pump gears or body are worn.

You should always set the valve with hot oil. On my oil pump test rig if I set for 80 psi when cold it gives 60 psi when hot. A detailed study in fluid dynamics might provide a scientific explanation.

But yes I would first adjust the relief valve to get 70 psi with hot oil, if you can, or fit a new spring if it is not adjustable.

[Moises]

Thanks Keith. I adjusted the oil pump relief valve with cold oil. I will remove the oil pump again and check it with warm oil.

[Forumadmin]

Although adjusting the relief valve may improve the oil pressure when warm at high revs, it probably will not improve at low revs.
Jowett's introduced a higher capacity pump when they realised that increasing the flow of oil to the bearings was required and they increased the diameter of the oil delivery pipe.
The flow increases as the viscosity of the oil decreases due to temperature and this reduces the back pressure sensed by the relief valve.viewtopic.php?p=23559#p23559
My test bed has a valve that I can adjust to limit the flow and thus increase the pressure until the relief valve opens. But the relief valve is also slightly affected by the temperature of the oil. viewtopic.php?p=23555#p23555
I would not adjust the relief valve to give a pressure higher than 90psi when cold as things will start bursting!

Note that the oil pump should have a very thin plastic gasket between the body and base. I had one pump where this had fractured causing aeriation of the oil. Oil pressure ok but it would soon have damaged bearings.

I can tell on the test bed if the pump gears are worn as the pressure increases slowly as revs increase. I use a variable speed drill to test. viewtopic.php?p=23560#p23560

[David Morris]

Hi Moises,

The replies from Keith set me thinking. We had rebuilt an engine, with the later oil pump, ( which unfortunately we didn't check! ) that when started for the first time the oil gauge needle went off the end stop! It was certainly in excess of 100 psi and meant burst pipes and oil everywhere!

It turned out that the oil relief valve was stuck shut with rust! Perhaps yours is stuck open? I think this would mean a reasonable oil pressure when cold, dropping to almost nothing when the oil is hot, as everything is being sent back to the sump from the pump with the valve stuck open?

Could yours be stuck open?

Best regards,

David

[Moises]

Good morning Keith and David, When I checked the oil pump in December 2022 and tested it following Keith's instructions the valve was working correctly. I had one fault. I only did the test with cold oil.
Another question: The oil pump cover is worn (see photo). Can this influence the pressure loss?
Thanks for your help

OIL PUMP TEST.mp4

OIL PUMP COVER.JPG

[Forumadmin]

Thanks for the video. The simple answer is a worn base would cause loss of oil pressure at low revs as it allows leakage of the pressurised oil. I have not quantified the volume of oil pumped for a given number of revs but will try to remember next time I do the test. However, the viscosity of the oil will make a considerable difference.
Remember the original design was built for SAE 30 so 20/50 will probably be thinner when cold and thicker when hot.

The oil pump rotates at half engine speed so I would expect full oil flow and pressure at 500rpm on the drill.

[Keith Clements]

If you look at Philip Dingle's viscosity chart you see that SAE 30 at 90C has a viscosity of 8 centistokes. So a fluid at 20c with the same viscosity would be fuel oil. Even SAE 10 needs an oil temp of 76C for the same viscosity. Diesel has too low a viscosity, needing -6C to be 8 centistokes.

[David Morris]

Hi Moises,

Thanks for the video. I can see that the pump base plate is worn, but not sure how much this would affect the pressure when the oil is hot?

Your test rig for the pump looks very good. Did you try altering the setting for the oil pressure relief valve, to see if the plunger in the valve was 'free'. I still think it might be stuck open or that the valve spring has failed, so then the only thing that controls the delivered oil pressure would be the viscosity of the oil and the effect of the wear in the pump? The oil would naturally get thinner as its temperature rises. My Javelin's oil ran much hotter than the water temperature and you could almost burn your finger on the dip stick when she was running at the correct water temperature!

All the best,

David

[Moises]

Hi David, I seem to recall that I checked the valve's operation. However, I will soon remove the oil pump and test it with hot oil.
Thank you very much for your comments
Best wishes

[Keith Clements]

I have found that a wear ridge sometimes occurs in the relief valve bore. You might be able to ream or lap it out. Scott and I had immense problems with the valve on our cross USA and back trip when the valve stuck open. I think Scott cured it with another base.
viewtopic.php?p=16861&hilit=relief#p16861
viewtopic.php?p=16850&hilit=relief#p16850