Bruce :
On a TR4A, the line from the carb to the distributor is for the vacuum
advance, which is not active at idle. It's not a critical function, it's
only purpose is to improve gas mileage under cruise conditions. It also
helps a little with overheating and throttle response.
Your oil pressure does seem low, but it's not clear why. The most common
reason is probably worn bearings in the engine, but there are several other
possible causes that are all easier and cheaper to fix, hence worth checking
first. If the pressure is always proportional to the engine rpm, then I
would suspect worn bearings and/or oil pump, or something caught in the
pressure relief valve, or possibly too thin an oil. I've found that
multiple-viscosity oils sometimes lose their viscosity improver quickly in
my TR3 engines. But, if the pressure comes up to 45 psi and then stays
pretty close to that value, I would suspect an inaccurate gauge, or a weak
pressure relief spring.
I would suggest first trying a 'known good' pressure gauge. I found a cheap
mechanical pressure gauge at the local discount car parts store for $15 that
I use as a diagnostic tool (also good for checking fuel pressure on fuel
injected cars). If it agrees with your dash gauge, then try pulling out the
pressure relief valve (it's that big nut on the oil filter head with a
smaller nut and a slotted screw sticking out of it). Note the setting of
the screw (which adjusts the relief pressure) before disassembling and
cleaning it. If no problem is evident, put it back in the car, and turn the
adjustment down another turn. Also, try changing the oil, using the
recommended weight for your climate. If none of this helps, then start
planning your engine rebuild.
You can generally bring the oil pressure back up at least once, by dropping
the pan with the engine still in the car, and just changing the rod
bearings. I believe the Haynes recommends this as preventative maintenance,
every 30,000 miles. While you've got the pan off, pull the oil pump and
inspect it for clearances and for a cracked outer rotor. The end clearance
can be reduced by lapping the body down a little, either with some wet/dry
sandpaper on a sheet of glass, or with valve grinding compound and the end
cap.
Best, of course, is a full engine rebuild, but just changing the rod
bearings (and the mains, if you're adventurous) will likely extend the
engine's life for a year or two, while you save your nickels and dimes ...
Randall
59 TR3A daily driver - with a "poor man's rebuild" almost 3 years ago ...
Bruce Robertson wrote :
>
> Hello, I seem to have a problem with my oil pressure.
> My shop manual says that while driving at speeds over
> 30MPH oil pressure should be between 65-75psi I am
> running at about 45psi. Is this going to hurt my
> engine? and why am I low (is this a gage problem?) at
> idle I get about 15psi (which I assume is normal)
>
> Q#2 what does "the" vaccuume line that runs from the
> carbs to the distributor do??? (mine doesn't seem to
> do anything) my engine idles the same whether this is
> attached or not. is the vaccuume from the carb to the
> distributor, or the other way around, because I don't
> seem to have any suction in either direction. It also
> doesn't seem to make a difference if I block the hole.
> Is this only at idle?
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