Ed, I want to start by saying that IMO it's unlikely that your oil pump is
the problem. 99 times out of 100, the problem is excessive clearances
somewhere else (eg rod bearings, main bearings, etc.).
> Thereafter, at idle it will drop to 20 lbs.
There's nothing wrong with that at all, for a "middle aged" engine. My
current TR3A engine is "living on borrowed time", it's only carried about 5
psi at hot, slow idle for quite a few years now, with no problems related to
low oil pressure.
> During summer months I use straight SAE 50.
You might want to try the 20W50 in summer, it should give you slightly
higher oil pressure since it's actually thicker than straight 50 weight, at
temperatures over 100C (and the oil in the bearings should be over 100C).
> Is this normal to see when using 20W-50?
It's a general indicator of engine wear. I wouldn't expect to see it that
low on a freshly rebuilt engine, but IMO it's perfectly normal for an engine
with over 30k miles on it.
> Is there an adjustment (oil pressure release valve) that can be made to
> increase pressure at idle? How done?
No. There is a pressure relief valve that can be adjusted, but it does not
come into play until near the peak oil pressure.
The oil pump is a "positive displacement" design, meaning it puts out a
fixed amount of oil per engine revolution. However, the other end of the
pressurized oil system is effectively a fixed size hole (the sum of all the
bearing clearances and so on) that passes a constant amount of oil (for a
fixed pressure and viscosity). So, the oil pressure would always vary with
engine speed, without the action of the pressure relief valve. When the oil
pressure starts to get too high, the relief valve opens and shunts some of
the pump output back to the crankcase. The relief valve for a TR2-4 should
be set to 70psi, and attempts to turn it up higher will only lead to
increased oil leakage. Below 70 psi it's completely closed, and so cannot
affect idle oil pressure (unless it's over 70 psi).
> How difficult to rebuild the oil pump? I realize I need to drop the sump,
> etc.
Not bad at all. Be sure to inspect carefully and check the clearances per
the book. Also check the screen out carefully, if any of the wires are
broken where they are soldered to the tube, it's probably best to replace
the assembly. One of the "Tech Talk" volumes gives Ken Gillanders'
suggestion for reinforcing the screen, which I highly recommend.
> Is just the two piece oil pump repair kit all that is required
> for a rebuild?
Be warned that there have been a lot of inferior oil pump repair kits
around; I've heard numerous stories of rapid wear and/or failure with
catastrophic consequences. IMO as long as it can be brought close to the
specifications in the manual, it's far better to keep the original pump
components.
> Would it be better to pull out the pump, filter/mesh, etc and clean?
The pump is easy enough to remove once the pan's off, if you're going to
mess with it at all, I would certainly remove it. It's tough to check the
end clearance with it still on the engine in the car.
But before I'd mess with the pump, I'd change out the rod & main bearings.
The Haynes actually recommends doing the rods every 30k miles since they're
so easy to do and regular changes will help prolong the life of the crank.
The mains are only slightly more difficult to do with the engine still in
the car.
But for 20psi at hot idle, I wouldn't even bother with that.
Randall
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