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The time came to turn the engine over for the first time. No nasty noises but after about 15 seconds cranking the oil light is still on. Any recommendations for a suitable gauge to check the actual pressure?
Many thanks.

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Just to clarify I did fill the pump with vaseline and filled the filter with oil as well.

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As you've been doing, keep a close eye on the gauge. On a new build, I think it will take longer than 15 seconds to get oil pressure.

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Sorry, not gauge but light

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You shouldn't need to pack the oil pump with Vaseline, that was only needed on the older Classic engine (the one with a distributor), the P38 engine has a self priming oil pump. It won't have done any harm thought but as Harv says, if you are just cranking it on the starter, it'll probably need more than 15 seconds from completely dry.

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Thank you Harv and Richard. I'll give it another go tomorrow. Is it possible to reassemble the pump gears incorectly? It's the only thing I can think of that I might have done wrong but I did check pretty carefully.

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If you’re worried, you could remove the oil pressure switch and plumb in a pressure gauge to get an idea of what is going on.

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Mine takes a good 30 seconds for the oil light to go out after changing the oil, even if I fill the oil filter up completely before fitting it. The light goes out instantly when I start it up normally, so I don't worry about the pump.

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Would it help to take the plugs out? Thinking it will crank faster so oil light will go out quicker while there won't be as much weight on bearings in case there is no oil pressure.

A mate used to have a race spec engine from a 70's 3L Capri in a mk2 Escort, it had a manual oil pump he'd pump a few times before starting the engine. Could anything like that be plumbed to the oil pressure sensor port to get oil around the engine and speed up the time it takes for the oil light to go out next time you time cranking?

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I’m with the others, it takes a while but it will go out, I was exactly the same when I rebuilt my engine on start up,, as for could you have put the gears back in wrong, it’s highly unlikely, as long as you tightened up the screws on the plate that holds it in you should be fine,, fire it up and hold your breathe,, it will go out before you can’t breathe

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If it's any consolation, when I first got my Classic, it needed to idle for a good 20 seconds before the oil pressure light went out if it had been left overnight. Admittedly that was down to the previous owner fitting a Britpart oil filter with no non-return valve so the entire contents of the oil filter would drain back to the sump. That was the previous generation engine with the non-priming pump too and it didn't suffer any untoward affects.

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Thank you all for the reassurance. I have taken the plugs out so it does spin over nicely. I'll give it another go this morning and try a gauge if that doesn't work. 1/8 npt i think?

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Popped off the pump to oil cooler pipe and no oil there so not looking good.

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It's not a bad idea, with your plugs out, to spin the engine with the starter until your oil pressure builds up, maybe 45 seconds or so. A sort of poor man's pre-oiler.

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I would have thought as V8 realise more on volume than pressure you would have oil circulation after about 30 seconds ---- is pump actually engaged ---- I've no idea about gems or Thor V8 I've built my Buick 300 tho which is basically same as old 3500 V8 but iron block not aluminum

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30 seconds is probably enough. I wrote 45 to make sure.

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So, with the pump to oil cooler pipe disconnected and a thumb over the outlet whilst it is cranked I could feel no pressure and no oil came out.

Would that indicate that there is a problem with the woodruff key driving the pump. It was a new one. I can't think what else it could be.

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If it was me, before tearing everything apart again, with your spark plugs removed, I would crank it over with the starter for a couple of minutes if needed, and then try it again (still with plugs removed). You shouldn't do any harm to the engine, as it is only turning any not building any pressure. Also, your starter motor won't be worked too hard as it isn't fighting any compression. I would be very surprised if the woodruff key failed.

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Harv, sir, you are a man of fine judgement!

Gave it a run with pipe disconnected and finally got a bit of flow and reconnected the pipe and after a minute the light went out.

You are my hero and I owe you a beer or better still a case of beer.

Thank you for saving me from a pointless strip down.

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Great news. If we ever meet, I'll join you for a beer. But helping each other out on our P38's is what we're all here for, so no need for you to buy. I'm glad to hear it works!