> I posted this message a couple of weeks ago but really havent seen
> any information that would answer any of my questions. So here it is again.
Sorry, I must have missed it. Here goes...
> I have a 67 mgb with a recently rebuilt engine. I belive I may have
> a oil pressure problem and thought I would throw a few questions out
> to anyone who may have some experienced similar problems.
>
> 1. What should I expect for oil-pressure out of a fresh motor? I am
> seeing 10-15 psi at idle and 50-60 psi at 2000rpm. I am using
> straight 30wt. When the motor is warmed up and the engine is at
> idle the pressure drops to 10psi.
That's at the low side of acceptable. I don't know where you're located,
but if the intel.com address means Santa Clara, run 20W-50 Castrol GTX all
year round and you can't go wrong. Do NOT run straight 50-weight Castrol
racing oil, or you'll blow your bearings when the weather drops below
60 degrees. In fact, I would advise against running a straight (single-
viscosity) oil under any circumstances other than pure track use, and
even there, modern synthetics and modern VI enhancers (no, that's not an
awk script) are almost as large an improvement in lubrication as modern
tires are in adhesion.
> 2. There also is about a 30-45 second delay before I see any movement
> on the oil gauge when the engine is first started. This seemed a
> little slow to me.
30 to 45 seconds is way too long. 15 to 20 is normal. You need to
use a wider viscosity range in that car, for starters. And apropos the
other discussions, are you running *enough* oil in the car? My Car-nak
the Great diagnosis of this (hey, don't knock it, I'm actually a Jedi
mechanic :-) is that the 30wt is too thick when cold so it takes too
long to get pumped to the bearings, then it's too thin when hot so the
pressure drops. The 20 part will help symptom 2 from your list, while
the 50 part will help symptom 1. (And if you say "But Castrol GTX is
so much more *expensive* than Flag 30-weight!", I'm afraid you'll have
to give me your car. It's the law. :-)
> 3. I also noticed that when I am running the engine at 2000+ rpm
> the gauge reading isn`t steady. The gauge reading bounces between
> 50-60psi. It seems to bounce with a fairly consistant cycle.
That's the rocker shaft. Who "rebuilt" this engine and what did they
consider a "rebuild"? What happens is that as the bushes in the rocker
arms wear (or as the rocker shaft itself wears, more commonly, because
the porous bronze of the bushings absorbs the oil and protects itself --
paradoxically, it's almost always the harder metal that wears when two
dissimilar metals are in contact), the gap between them becomes uneven,
tight at one part of the cycle and loose at another part. This shows
up as a fluctuating oil pressure gauge, common on MGBs.
If you are in Santa Clara, go to O'Connor Classics on Scott near
Central and buy a new rocker shaft assembly. They're $150. They
don't require a core, so you can buy the shaft and install it on
your car at leisure; takes about an hour and a half if you work
slowly. You will of course need to readjust your valves twice --
once cold (for initial settings) and once after the car has warmed
up. Remember that the big 9/16" nuts take a 40 to 45 lb-ft setting,
while the little 1/2" nuts take only 25 lb-ft, and they will strip
at the slightest provocation. (And if you *are* in Santa Clara,
call me at (408) 441-3141 and I'll work out an exchange -- I'll help
you install the rocker if you help me get The Green Car running. :-)
> 4. Do these symtoms sound like a bad oil-pump? I have already
> replaced the pressure-relief valve just in case it was the
> problem.
Not necessarily. I'll bet that the rocker shaft will cure not only
the wobbling gauge, but will also bring the rest of your oil pressure
up between 5 and 15 psi under all conditions. Going to the proper
weight oil will help too, *as will keeping it topped up or if anything
just slightly overfilled*.
> Any help would be appreciated. I have called several shops and
> haven`t got the same answer from any of them.
Well, note that diagnosing electronically -- whether voice or ASCII --
is always difficult. But the wobbling gauge is the key to my diagnosis
as the rocker assembly; I've had that problem and fixed it that way on
a couple of different MGBs. Tell us more about what "rebuilt" means,
though, as it has almost as wide a variation in meaning as "restored."
--Scott "Rebuilt means never having to say, `Hello, AAA?'" Fisher
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