[TR] Oil Pressure

[Brad Kahler]

This thread reminds me of a conversation I had with Kas Kastner at a race we
attended at Mosport a few years ago.

I was working on Susan's 1300 spitfire engine trying to sort out a low oil
pressure problem.  As is typical of these events I had plenty of help and
assistance from all of the other Triumph racers.  Of note was when Kas was
helping me troubleshoot the oil pressure problem.  During our conversation we
discussed the concerns of having to little oil pressure, especially at high
rpms (i.e. 6000 and up).  Obviously at higher rpms you don't want to see low
oil pressure and you would expect to see max pressure at that time, which was
what we weren't getting.  I asked Kas what he felt the top end limit for oil
pressure should be on Susan's 1300 engine.  He kind of surprised me when he
said if he had his druthers a high oil pressure reading of well over 100 psi
would be his choice (I don't remember the exact number but it was more than
you would think).  He agreed there would be hp loss due to having to run a
pump that high but his thought was a healthy flow of oil helped keep the
engine running smoothly and helped it survive in high rev conditions.

During Susan's last race at VIR this spring we noticed on the last day that at
idle her oil pressure had dropped to 20 psi or so when it used to be around 60
psi.  High rpm pressure was about 70 psi.  At that point we elected to put the
car on the trailer rather than risk the engine.  Such is racing.

Anyway, I always remember that conversation when I read threads like this
where people seem to worry about having to high of an oil pressure reading.  I
no longer worry about having to much oil pressure. When I see a drop from what
it normally runs THAT is when I start to worry.

You can interpret the conversation I had with Kas anyway you want, I know how
I've interpreted it...........

Brad


On Wed, Sep 16, 2009 at 12:58 PM, Randall <tr3driver at ca.rr.com> wrote:

> I was not aware of this valve, does
> it regulate the oil pressure in the engine or just to the gauge?

To the engine.

> If to the
> engine, could it be part of the reason I am seeing excessive leaking from
> my brand new rear main seal?

Could be, though I think it's unlikely unless your rear main bearing is
tired.  The rear main seal does not have to seal against the oil gallery
pressure, there is a big drain hole to carry away whatever oil leaks from
the rear main bearing.

> Right now, most of time, driving at 3000rpm yields a pressure reading of
> 80-90psi.

A bit high, but only a bit.  The book says the pressure relief valve should
open at 70 psi.  However, it doesn't immediately open fully, so the pressure
can rise above 70 psi if there is a lot of flow through the valve (as there
will be with a tight, cold engine).

Long time ago, I ran straight 40 weight oil even in the winter time.  Worked
well in the tired old engine, but after the rebuild it would peg the oil
gauge on cold starts.  Didn't seem to cause any excess leaks (but I did
switch to lighter oil at the next change).

The usual causes of leakage from the scroll-type rear main seal are excess
crankcase pressure; and clearances too large at the seal.  The factory
workshop manual appears to have a misprint on the drawing for the setting
mandrel, which of course has been copied many times over the years
(including the setting tools sold by some vendors).

-- Randall
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