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+--- Thread: Help - oil pressure / flow on engine first start. (/showthread.php?tid=5904)
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Help - oil pressure / flow on engine first start. - Neil D - 04-04-2021
I'm looking for some advice and help. I've come to star my enginefor the first time with the car in my possession and I don't get any oil pressure when cranking, I've also removed the pressure tapping on the crank case and don't get any flow.
The the is on 12v with a 6v starter so cranks quite quickly.
I've had the sump off and all looks OK, pump drive etc.
Would I expect oil pressure or flow at cranking?
I've not yet inspected the pressure relief valve, are these known to stick open?
It's an early coil engine
Any suggestions / advice?
Thanks Neil
RE: Help - oil pressure / flow on engine first start. - Robert Leigh - 04-04-2021
I would expect to get oil from the pressure tapping when cranking the engine, particularly at 12v speed. I once failed to notice that I was fitting the wrong generation of rear bush for the camshaft; there are two different outside diameters, and the smaller one in the larger crankcase bore allows any pressure from the pump to be dissipated outside the bush straight to the sump without circulating through the pressure system.
RE: Help - oil pressure / flow on engine first start. - David Cochrane - 04-04-2021
Could it be upside-down oil pump vanes?
Do you know for certain that the engine was running with oil pressure before the car came into your possession?
RE: Help - oil pressure / flow on engine first start. - "Slack Alice" Simon - 04-04-2021
Yes, oil should flow from the gauge take off. Once the system is primed I would expect flow even on hand cranking.
It could take half a minute or so for the system to prime if being run for the first time in a while.
I think there should be flow even if the oil pressure relief ball is not hard on its seating.
How much do you know about the engine?
Could it have the wrong cam rear bearing?
If it has just been thrown together and dropped in the car:
Is the camshaft - which drives the oil pump - actually going round?
Does the oil pump actually have vanes fitted? and are they being driven round?
RE: Help - oil pressure / flow on engine first start. - Ruairidh Dunford - 04-04-2021
Like Robert, I have seen the incorrect rear cam bearing fitted resulting in absolutely zero oil pressure.
Oil vanes fitted upside down or, one up, one down, will result in lower oil pressure but rarely none (at start up).
An ill fitting (something jammed under it) oil pressure relief valve can result in no oil pressure whatsoever.
This was a new (to me) cause of zero oil pressure I found recently...
RE: Help - oil pressure / flow on engine first start. - Alan - 04-04-2021
Even the slowest of tickovers should produce a fountain of oil at the disconnected pressure gauge union. Don’t ask how I know that. If the engine has been standing, my money would be on a stuck oil pump vane.
RE: Help - oil pressure / flow on engine first start. - Tony Betts - 04-04-2021
nice one R,
ive opened a few engines like that
a common one, after an engine has been worked on, on the bench. is the pump base plate stands proud of the sump. when moved it will clog with dirt.
check there are actually springs in the pump, and they are long enough to push the vains out.
a recent engine ive done, i didnt know the top gallery had been plugged to fit a filter. so although we got oil at the gauge pipe. there was no oil at the jets. but off the gauge with pressure.
you keep learning even after 30 years.
RE: Help - oil pressure / flow on engine first start. - Neil D - 04-04-2021
Thanks for the advice. I've got it fixed.
The cause was a number of these,
One oil pump vane in upside down which looks like it damaged the cover plate of the oil pump and a bit of the brass dwarf then jammed one of the oil pump vanes in the compressed position, I think it was the one in upside down.
Vanes and springs swapped for a spare set.
Cover lapped to remove the damage.
Swarf removed from oil pump.
Checked for oil at the jet access plugs - all ok.
I now have oil pressure on the starter.
Just need to get the down draft Zenith and ignition timing sorted so it will run for more that a couple of seconds.
Thanks Neil
RE: Help - oil pressure / flow on engine first start. - David Cochrane - 04-04-2021
The cause of the wrongly-placed oil pump gasket could well be because of the highly misleading illustration in Austin's Lists of Spare Parts, which show the gasket between the cover and the body. These illustrations are not like a modern exploded diagram, but it's all too easy to assume that illustration shows how it should be assembled, especially if you're not familiar with how the engine should go together.
RE: Help - oil pressure / flow on engine first start. - Ruairidh Dunford - 04-04-2021
I suspect you could be correct David.
It is one of the reasons that I don’t think they are a good source for accuracy, interesting to look at however.