[TR] Oil Pressure

[David Brister]

After an engine rebuild my TR4A oil pressure was adjusted on the bypass 
valve spring to 70psi hot at 2000rpm. This gave around 30 at 800 idle hot. 
After about 50k miles I noticed that after a long blast at 3500 revs in hot 
weather on a motorway on returning to "normal" driving the 2000rpm  pressure 
would have dropped to 40-45 and idle  5-10psi. This would gradually recover 
as one continued in normal road driving.

I dropped the sump and changed the big end bearings (which did'nt show much 
wear) and oil pressures returned to normal in all conditions. I have always 
used 20/50 or 10/40 oil. Which oil I use does'nt seem to make any difference 
to the oil pressure. Whilst I agree with Randall that you can drive safely 
with low oil pressure I believe that will cause the bearings to wear 
quicker, particularly the mains.

There is occasionally a drop in pressure from 70psi to around 30. That is my 
cue to stop and remove the oil pressure relief valve and clean the ball 
which has picked up a bit of muck between it and the seat.. When you have 
done this a few times it does'nt take much effort or time. (You have to note 
the turns needed to remove the adjusting screw). When I acquired the car 
Pete Cox told me that if the 2000rpm pressure dropped below 50 or so it was 
time for action.

YMMV of course,

David Brister,
1967 TR4A. 


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