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Re: Going to look at a 1971 B-GT: oil pressure problem

To: Mark Dawson <torchbone@bright.net>
Subject: Re: Going to look at a 1971 B-GT: oil pressure problem
From: Rocky Frisco <rock@rocky-frisco.com>
Date: Thu, 17 Jan 2002 12:53:37 -0600
Mark Dawson wrote:
> 
> I'm off in the morning to look at buying a B-GT, and had one question for
> the list. Since I've had an MG for a year and a half, I have an idea of the
> usual things to look for in terms of rust and whatnot, but the current owner
> says one thing that I don't know what to do with:
> 
> "I don't know about driving it a great distance. After about 25 minutes the
> oil pressure drops off. Now these MGs, they don't have oil pumps, they have
> springs and relief valves and stuff..."
> 
> ...yes. Well. Anyhow, what would cause the pressure to drop off, except for
> a leak? It must not be leaking, because the pressure is evidently back when
> he restarts.

My guess:

Heat-related: when the oil thins some with heat, the pressure goes
down.

Reason: Possibly the pressure-relief valve is jammed partly open. I
have had this happen after a heavy thrash in the Minis and once in a
Frog-eye.

I just remove the pressure-relief valve cap and spring and withdraw
the plunger. This can be hard if it's stuck. I usually can withdraw
it by using a wooden dowel sanded down to a fairly tight fit inside
the plunger. Once I actually had to use an oversized easy-out. In
the Minis it's more of a problem, since the transmission is in the
sump and that introduces a fair amount of swarf into the equation. 

We Mini folk often use a ball-bearing of the right size instead of
the plunger. Even so, I have had to remove and clean the ball and
valve area twice now because even the ball can be held off the
sealing ring if a bit of swarf manages to get in there and then be
trapped by the spring-loaded ball. Sometimes after cooling all
night, the higher oil pressure the next morning can lift the ball or
plunger, freeing the swarf to go on down the passages and into the
filter.

I would try to disassemble the relief valve and clean everything
thoroughly, then reassemble it and recheck the oil pressure.

-Rock  http://www.rocky-frisco.com
-- 
Red Dirt Rangers (Rocky on piano): http://www.reddirtrangers.com
JJ Cale Live (w/Rocky): http://www.rocky-frisco.com/calelive.htm
The Luggage Fan Club: http://groups.yahoo.com/group/luggage-fans

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