I've seen the same thing on my car and others have speculated that it was
the relief valve/spring. Mine were new. I don't remember it doing it before
the rebuild. I wouldn't worry about it...
Chris
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From: mgs-owner
To: mgs
Subject: MGB OIL PRESSURE VARIATION
Date: Thursday, June 06, 1996 1:35PM
I am soliciting NETWISDOM from you SOL partners, I have an interesting
phenomena to share.
I have recently completed my 76B restoration and part of that was the
the rebuilding of the motor.
The block was bored +20 over,the crank was ground -10, new cam, oil pump
bearings, thrustwashers, timing chain, gears, tensioner etc etc.
The cylinder head was reworked, new guides valves, seats, rocker shaft
springs,etc etc, oh I forgot to mention, new oil pressure relief assy.
The block was "tanked cleaned" by a reputable shop and they cleaned the
oil passages and replugged the ends.
I used assembly lube during assembly,torqued everything to the BENTLEY
specs. It other words I assume I have a NEW motor. Now we come to the
interesting and at least for me, puzzeling part. When I start the
the engine I get 80-90lbs pressure at 1500RPM, at idle 900 RPM I get
70lbs. at 2000-2300 RPM the oil pressure gauge is flickering quite
violently 25-30lbs variation. If I let it idle down pressure is rock
steady again. What is happening? Is the pressure relief valve opening
and closing causing this fluctuation, or is the pump cavitating?
I was realy concerned at first thinking I had screwed something up on
assembly, but the more I think about it the more convinced I am that
I do not have so serious a problem as no lubrication because of a pump
failure. When I was ordering parts I think I saw advertised a high
capacity oil pump and may be thats what I got, but that was a while ago
and I could not be certain that this is the case.
My guess is,that the observation of fluctuating oil pressure is caused
by the oil pressure relief valve opening and closing, but why?
Have I got a high capacity oil pump- is there such a thing?
Should I be concerned? What should I do, do nothing and it will go away?
Nah. Should I pull the engine and replace the oil pump? (I hope not).
Should I replace the oil pressure relief valve assembly? How about the
gauge, could it be bad?
One thing I did not do that has been eating at me, I did not bleed the
oil pressure gauge line, so could I be seeing the resulting higher
fluctuations because the column of air in the pipe is being compressed
and released as the oil pressure goes up and down at a lower rate? Nah!
Just what could be causing this? Should I try to use a more reliable
or accurate gauge to confirm what I see? Can anyone shed some light.
I am running castrol 10/30 oil and a "LUCAS" oil filter, I had no idea
they made oil filters, I hope this is not my problem.
Some of you more experienced race car specialists may have some ideas.
Please respond either direct or to the digest, which ever you feel is
more appropriate. Thank's in advance - John.
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John Bartholomew AMDAHL SAN JOSE CA. Usual disclaimers apply
69 BGT, 74 MGB, 76B restored, 79 MGB for sale, 72B daily driver.
408-746-6361 (07:00-16:00 PDT) via internet jdb70@amail.amdahl.com
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