There's still one thing I'm trying to clear up about the various holes
in my engine block. Between my oil pressure switch and oil pressure
relief valve is what appears to be an open "hole" in the engine block.
It's about the same size as the oil pressure switch/relief valve hole,
but there's nothing in it. Is this normal or should it be plugged?
Thanks,
Dwayne
-----Original Message-----
From: Robert M. Lang [mailto:lang@isis.mit.edu]
Sent: Thursday, December 20, 2001 6:37 AM
To: Dwayne Cooper
Cc: 6pack@autox.team.net
Subject: Re: A couple of things...
On Wed, 19 Dec 2001, Dwayne Cooper wrote:
> I'm still trying to get my '74 on the road and have come across a
couple
> of issues:
Okay.
> 1) I started rebuilding the carbs and in the process found out that
the
> hex adjusting "cap" for one of my adjustable metering needles was
> stripped out. I was able to remove it with a little work and promptly
> ordered a new adjustable metering needle from Moss. Unfortunately,
the
> new needle did not include the hex adjusting "cap". Does anyone know
if
> these are available somewhere?
I can't speak to this. I have wound up scavaging parts from other carb
sets in a pinch... I usually have at least two or three sets of carbs
hanging around.
> 2) My oil pressure line isn't attached to anything and I can't quite
> figure out where it goes. It looks like there's a hole underneath my
> oil pressure switch that could be fitted with the adaptor I see in the
> moss catalog, but I looked under the hood of a friend's TR6 recently
and
> noticed his was attached closer to the firewall. The spot where his
is
> attached has been capped off in my car. I'm also curious as to what
the
> oil pressure release valve does -- is it the longish bolt at the
bottom
> of the block underneath the oil pressure switch?
Okay - I have to make an assumption here. I think you are talking about
the oil pressure line to the pressure gauge in the cockpit. If so, the
tap
is on the side of the block towards the rear on the drivers's side (I
assume also that your car is LHD). If your tap is capped, you need to
figure out why.
The setup is that there is an adapter that goes into the block. The
adapter is 1/8 NPT into the block, and the other side is 1/8-27 BSP
(British Standard Pipe). If you don't have that adapter, you have a
bunch
of choices available to you - all are "plumbing projects", but fairly
simple.
Now you mention that your oil pressure switch is set up with some sort
of
adapter. The oil pressure switch goes into the block just beneath the
distributor. By chance, this is also an 1/8 NPT fitting. Either location
is probably okay for the oil pressure guage tap location, as they both
are
located on the main oil gallery along that side of the block.
If you want original - then you should use the rear tap location.
The oil pressure relief valve is more or less self explanatory. If
anything causes the oil pressure to go too high (defined by a spring in
the oil pressure relief valve, then the valve opens and allows the
pressure to drop. This is done so that the pressure is not too high
anywhere in the system so that you don't do bad things like hurt the
bearings or possibly collapse the oil filter (or burst it if you have
spin-on). As you might imagine, the process of oil pressure relief is
actually "dynamic", the valve opens / closes all the time that the motor
is running.
Pay attention to that valve! If it "sticks" you will do the following:
stuck open: the oil pressure will be very low - maybe 20 pounds max. If
you try loading the motor at all with pressure this low, you will hurt
your bearings (at best) or trash the bearings and possibly ruin your
crank
and/or the rods.
stuck closed: the oil pressure will be very high. This will cause the
oil
gauge to fail (when the pressure goes over about 110 PSI) and will
likely
cause other problems due to not enough oil _volume_. In fact, if the
orifice is completely closed, I think you only get oil to the main
bearings - bottom line: you don't want this any more than you want oil
pressure too low.
I know the above from my race car. I've had both problems - ironically
with the same valve. I was lucky and only fried one bearing and the
crank
was undamaged. If I'd been "stupid" and kept running the motor after I
heard the telltale rod know, things would have been much worse. I also
blew two stock Smiths gauges before I realized that the guages were
right
and I was being stupid by not tracking down what the oil pressure
actually
was! Had I been a bit more savvy, I would have connected a known working
guage to the motor and measure (in this case a guage that could read
more
than 100 PSI) to verify the actual pressure. Doh!
When you go inside the engine, pull the pressure relief valve off the
block and check it. For around $10 or $15 you can replace the plunger
(usually you need to do this because it gets "ridges" on it), the spring
(you don't necessarily need a "heavy duty" spring, BTW) and the copper
sealing gasket. Note: you can re-use the copper gasket provided that it
is
still flat and that you "anneal" it before reassembly. But make sure you
reinstall it correctly as this is a very important seal on your engine -
that thing fails, you can easily blow all your oil out very quickly, and
there's some large pressure numbers in that chamber (especially when
cold
or at higher RPMs).
If you have higher milage on your car, you might want to check the
status
of the oil pressure relief valve every year or two. The nice thing about
the TR6 setup is that it is fairly easy to access the pressure relief
valve..
> Thanks in advance for your help and advice.
You're welcome.
> Dwayne
rml
TR6's
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