Series 1 3.8 low oil pressure after fresh engine build..Help!

[Tom W]

I wonder if your problem is with the oil pressure relief valve? When the pressure went off the gauge, it could be the relief valve stuck closed. Similarly, if it fails to make more than 10psi, it could be explained by it sticking open too. If it’s a new part, maybe it’s faulty? You could try substituting it for your original part, as you say everything was working properly before the engine was rebuilt. You can test if the valve is working by temporarily clamping the oil bypass hose while the engine is running. The pressure should climb. If it doesn’t, the cause of the low pressure is somewhere else in the engine and there’s no flow through the bypass.

[abouttownman]

Hi Steve

Curiouser and curiouser! Yes I had noticed my 5th hole which is obviously redundant. As I have had no issues with it previously I see no need to plug it though will take further advice on it. The hole does not go into any galleries so no risk of a leak from it. My car is a late 64 UK supplied 3.8 with matching numbers so I imagine the blocks were by that time pre drilled with 5 studs in preparation for the new model if indeed the 4.2 cars had a 5 stud filter housing?
If anyone is able to describe the flow of oil route from the pump I would be grateful to learn it,as this will give me a better understanding of where my pressure could be going.
Unfortunately the workshop manual does not go into much detail on this subject.
Mike

[mgcjag]

Hi Mike...found this on the US JL forum....may be of intetest. Dont know if its acurate...the post under this photo was posted by one of our experts on XK engins....Steve

NB On later engines the sump return is external (no front hole) the small main feed drilling is plugged (all mains fed from oil gallery).

[abouttownman]

Hi Tom

Yes I have tried clamping the return pipe and no it does not make the gauge rise.. the pressure relief valve seems to move freely enough though again I’m not entirely sure how it is supposed to operate. The balance valve again is a fairly simple set up with a ball and spring, before installing I spayed some WD40 into this to see if it leaked past the ball and it didn’t.
As mentioned I haven’t ruled out that my machine shop may have made an error with the crank re-grind or bearing clearances but as the engine is not making any disturbing noises it’s encouraging that the fault lies elsewhere. I should have a more conclusive answer after the mechanical wet test.

Thanks Steve, that’s useful I will have a study and hopefully become enlightened!
Mike

[mgcjag]

Hi Mike....You have a pressure relief and a bypass valve......if iv got this wrong someone will let us know....if pressure builds up the relief valve opens but the pressure then drops so the valve closes..etc...the bypass valve is incase the filter gets cloged then oil bypasses the filter......does this sound right......Steve

[abowie]

I am not sure what was referred to in the earlier post regarding rear camshaft plugs?
Thanks again for all your comments.

The camshafts are hollow and oil is fed into them via the rear bearing shell. At the rear of the camshaft the bore is threaded. the tacho drive dog seals the inlet cam and on the exhaust side there's a bolt with a copper washer.
What I'd be doing at this point.

1. Ensure that the car contains at least 8.5l of proper oil.

2. Ascertain that you do really have low oil pressure. Connect a known good mechanical gauge. Remove the plugs and run the engine on the starter. You should be able to generate 40 psi within 30 seconds and it should hold.

2a. It looks like you have a new oil pressure sender unit. These are notoriously inaccurate. Hook it up to 40psi of compressed air via an air compressor and see what your dash gauge says. If you have your old one fit that and see what happens.

3. Ensure that your overpressure valve works. I'm sorry that I don't know enough about these to troubleshoot it other than to say that the spring length is critical at 3" and that the plunger can be put in the wrong way round or can fail to seat properly or be obstructed by swarf etc.

4. Replace your oil pump. I know yours looks to be working fine but the guys I work for routinely replace them.

5. Consider other unlikely causes. So my ideas about the camshafts. Have the oil gallery plugs been fitted at the front of the block and under the oil filter housing? Is oil making its way into the water passages somehow?

6. At this point I can't think of anything else but bearing to crank clearance. Plastigauge time.

To be honest, if this is a professionally built engine you shouldn't need to be doing this; they should be doing it for you.

[1954Etype]

As Andrew says, look at number 2 first. Hook up a mechanical gauge.

I had an engine that had been reground 20 thou but fitted with 10 thou shells on the mains. Oil pressure okish when cold but dropped like a stone quickly.

Could be that but go for the easy test first with a mechanical gauge.

[abouttownman]

Hi Guys

Thank you so much for your informed replies, I really appreciate all of your input..

Just wanted to update you and share my good news!
I managed to get hold of a mechanical gauge over the weekend and screwed it directly into the block to the right of the filter housing which I believe goes to main bearings according to the earlier diagram Steve kindly posted.

So as you will see from the images I will attach I have 60-70 lbs pressure cold on the mechanical gauge which drops to 45-50 when hot having allowed the car to run for 15mins.
You will also see my electric gauge still only records a tad less than 10lbs when cold.
Any way needless to say I’m a very happy chappy!
I think my issue with the electric gauge could be wiring which is what I will hopefully be finishing off this week. I’ve probably not got great earths or rather power feeds to body being the car has just been repainted.
I hope you guys don’t mind if I tap your brains again should I have any further issues with the rest of it.
Many Thanks

Mike

[abouttownman]

[mgcjag]

Hi Mike...great news......do yourself a favor and fit a mechanical guage.....also on your car i think your red ignition light is actually operated by an oil pressure switch fitted in the block further forward from the filter housing....this can be replaced with a low pressure switch rather than a no pressure.....All the best...Steve

[1954Etype]

Not on a 3.8 Steve. This 'feature' was only on the early 4.2s when they went to an Alternator.

[abowie]

Excellent outcome.

[mgcjag]

Thanks Angus...worth fitting one? Steve

[1954Etype]

Steve, personally I keep an e ye on the gauges so it wouldn't be worth it for me. Has to be a good idea generally though to have an additional warning light though!