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MG MGB GT V8 Factory Originals Technical - Oil pressure

Just fired up the four litre for the first time.
Sounds incredible.
Everything seems fine apart from the oil pressure.
Ran at 2500rpm for 10mins as cam instructions with about 40psi on meter. Drop the revs back to about 1800 and the oil pressure drops dramatically down to nearly zero. The guage is very jerky maybe it is faulty as the engine stays quiet. How can I tell if my guage is OK, or what could be causing the drop in pressure.
I am running the same front cover and oil pump as I had on the 3.5 as it had only done about 10k miles.

Polished up the stainless RV8 manifolds before fitting and now they have gone a deep gold colour with the heat, looks superb.

Mark
Mark Rawlins

Mark,

No oil pressure is not the best news for you. I would first try to borrow another meter and check the oil pressure. If it is really dropping there are theoretically 2 possibilitys: 1 you pump doesn't build up pressure under lower RPM. 2 there is a "leak" in the oil system which drops the oil pressure at a lower flow.
If the pressure is almost 0 at 1800 rpm, the pump must be really bad and i guess you should have seen when fitting. So i assume there is a pressure drop in the system. Because it is so dramatically, you shoud check the by-pass valve near the oil filter at first. Maybe it is leaking. If this oke there should be somewhere a spot where the oil can get out very easily. To check this you could remove the distributor and get a tool which you fit to a drilling machine which gets the oil pump to work. Remove the valve covers first and see if there is a spot where a lot of oil comes out if not you could remove the inlet manifold. i never did it but it may be a good method.
Good luck, i hope you find the cause quick.
Regards
Peter
Peter van de Velde

Peter
Thanks for the reply.
Before starting the engine I used an electric drill to operate the oil pump. When it fired up the lifters became quiet straight away.
For my own peace of mind I have just removed the oil pump cover and checked the gears,relief valve and spring. All seems to be perfect. I think the next step is to try another guage.
On refitting the relief valve I overtightened the plug and split the alloy cover so I need one of those as well now!
Mark Rawlins

For a new/rebuilt engine (if this is the case) the pressure is too low when the MGV8 style of oil pump base (and pressure relief valve spring etc) is used. The pressure cold should be over 50psi settling down as the temp rises.

SD1 motors with the standard oil pump base with the integral filter were notorious for running pressures around 35 to 40 at best with often next to no pressure reading when idling. These engines always did 150K plus miles thrashed night and day without failures.

One common fault that displays the pressure readings you have is a pressure relief valve which has stuck open. Obviously you have some work in this area now, but I suggest you look somewhat closer. I have had several situations in the last couple of years where oil pressure problems on new;u built V8 engines in MGs has been down to the pressure relief valve and spring. Do not assume that because the parts were new that it isn't that because the cars I have looked at have used new parts and there still was a problem.

Rog
Roger Parker

The parts came today.
Oil pump gears, cover, relief valve and spring.
Started her up and Perfect.
Mark Rawlins

Mark,

Good to hear the engine is oke now. Have some fun soon!!
Regards
Peter
Peter van de Velde

I spoke too soon.

The next day I started the engine and had the same problem.
I took the oil pump apart again (third time) and noticed that the sides were scored internally and the ends of the new idle oil gear teeth were marked. Somehow the teeth of the Idle oil gear are touching the side as the gear turns. The way I see it is that small particles of aluminium were being scraped off the casing of the oil pump and catching in the pressure release valve preventing it from closing properly.
I rubbed down the internal walls of the oil pump with fine wet and dry and also the tooth ends of the idle gear. Flushed out thoroughly and reasembled not forgetting to pack pump with vaseline. Fitted a different pressure guage and started her up and 40psi at 2500rpm but no oil pressure on idle.( in fact I held it at 1500rpm and the pressure was up and down like a yoyo from 5 to 25psi ). Phoned a couple of engine specialists who said that the probable cause is worn main and big ends allowing too much oil to escape and thus less pressure.
Feeling nearly suicidal by now I removed the sump and removed two of the main bearing caps and one big end cap. All three bearings look to me to be perfect, no sign of wear, nice white metal bearing surfaces that dont seem to have done much work. AAAAAAAAAAAARRRRRRRRRRRGGGG.
The plan now is to rig up a temporary oil pick up hose that will reach the sump on the floor. wip out the dist
and get a mate to start the pump with a drill. I will be underneath trying to look for big leaks probably getting covered in oil in the process.

Has anyone any ideas what to do next this is really doing my head in.




Mark Rawlins

Mark,

Out of interest who did you buy your engine from

Paul
Paul Wiley

Paul

I bought the engine from a guy called N. J. Evans of Kempston Hardwick Nr Milton Keynes. He had five complete engines. He told me that they had come straight from the production line at landrover as special engines had been fitted in thier place.
They looked brand new complete with all ancilaries.
As i had to use the SD1 front cover I needed a new camshaft with dist drive. Sent the heads off to Peter Burgess and fitted piper cam. Everything inside looks really good, like new. Bought as a second hand engine with no guaruntee.

Just need to sort this problem then It will be on the road.

Mark
Mark Rawlins

Mark

I know that it is doing your head in but you have to tkat a deep breath -have another cup of tea or whatever and think before rushing around undoing this and that and destroying the evidence of the original problem.
I think that Roger is right and it sounds very much like a relief valve that is sticking open at idle-bouncing gauge needles are nearly always caused by a relief valve opening and shutting rapidly BUT you must be methodical in your analysis:
Check the gauge-if neccessary get hold of a bigger gauge from somthing like a model engineers supply shop,industrial air tool suppies , hydraulic supplies etc so that you have a more accurate baseline.
You must examine the pump more thoroughly-and also check the bottom of the sump! The only way the pump gears can contact the the sides of the oil pump is due to excessive wear esp of the bore of the main gear bearing-was the cover BRAND NEW when you fitted it to your previous engine? The only other reason for the scoring that you mention is the cam lobes or the follower bases breaking up and the little pieces of chill cast iron gettting trapped between the tips of the teeth and the pump wall.Check engine cleanliness(galleries),the cam lobes and follower bases.
The other super critical thing that you must check is the end float of the gears. If you contemplate the design of the pump you can see that excessive end float will allow the pressurized oil to just escape past the top and bottom of the gears. Check as per the workshop manual with a straight edge and feeler gauge. Please do not use any thing other that the proper cover gasket which is very thin and black in colour.My oil pump base came with incorrect length allen bolts and a green gasket which was way too thick at about 5-7thou. The gasket is critical to the end float and ultimately the oil pressure.
I used a brand new Flotec repro MGBV8 cover on my engine and haven't had problems with the relief valve.They can stick-there is a company doing one which has a spherical end to the valve which apperently helps-and which is also adjustable.Most designs of valve also have passageways to drain oil from behind the valve to prevent hydraulic locking.
Have you got any oil cooler lines /oil filter head plumbed in the right way around?
Check for air leaks in the suction side of the pump circuit-eg O ring at flange to block on sucker pipe and that the pipe has clearance at the sump bottom.
For the record my presuures generally are 55-60psi on start up and about 25psi at idle.

I hope that this is of some help and let us know how you get on....


Regards

John Bourke
John Bourke

Mark,

I initially thought you should check all the bearings because it could be that 1 was fitted which has excessive play. But if this was the case the pressure never would build up. Since you report good pressure for short intervals, i assume the cause must be found more in the direction of Johns very thorough ideas.
Regards
Peter
Peter van de Velde

Tried again this afternoon.
Bypassed the oil cooler. Checked direction of flow through Filter, fitted new filter. New Oil.
My antics underneath with the sump removed were suggested by a chap at Real Steel, he really had me believing that the bearings were worn and dumping oil.
In the end I didnt try and spot anything leaking as i thought oil would be dripping from everywhere anyway.
At least I now know the bearings are OK.
I took the oil pump base off again and could see no signs of anything wrong, no scoring or marks of any kind.
Started up after first priming with drill.
45psi at 2000rpm warmed up for a couple of mins then let the revs drop to 1000rpm now 5psi.
So far I think I have eliminated:-
The oil cooler, Oil filter, oil pump gears, oil,worn bearings.
The timing cover is obviously worn in respect of the oil pump housing.
Maybe the next step is a new timing cover.

Thanks to all for your help I will keep you informed.

I will be at stoneliegh by the way if anyone fancies a chat.

Cheers

Mark.
Mark Rawlins

This thread was discussed between 10/02/2001 and 16/02/2001

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