Drooping Oil Pressure - 2016
Another technical article from the "Professor" aka Rob Bradford
Loss of oil pressure in our TR’s at any time is a sphincter tightening moment as it can so easily be terminal, but when embarking on a long trip with deadlines like catching a ferry a couple of thousand K’s away can quickly become quite distressing.
We were heading down to Melbourne for a Friday afternoon Ferry across to Tasmania so after driving for 4 hours we took a short break for the usual fuel and other stuff before heading from Grafton up through the Nymboida ranges on our way to Armidale, only to observe the oil pressure a tiny little bit lower than normal.
The tiny bit lower became just a bit more than a tiny bit as we progressed, with a loss of about 3 psi every 20 K’s or so. One can easily get fanciful when faced with this odd situation with all the possible causes racing around between the ears at a great rate. Perhaps due to having just finished a crank out installation of a new rear oil seal, was a bearing disintegrating? Or perhaps I had missed something out of the re-assembly process? Or, or, maybe deterioration of the oil pressure relief valve seat allowing the spring to gradually force the steel ball further into the seat until it finally bursts through.
Anyway by the time we got through the steep climb and hairpin bends there was a place to stop before all pressure was lost below 2000 rpm and time to take stock of our options.
I decided to take a look at the oil bypass pressure relief valve, so backed off the lock nut and gave the tensioner a 360 degree twist, which to my delight immediately provided 25 psi at idle and 65 psi at 2500rpm. Time for a cup of strong coffee and an ice cream to suppress the jubilation and disguise the concern about said seat regression in the valve housing.
We then made a stop in Armidale for a visit and conference with Rob Nunan who offered a spare housing assembly off his TR4, however the pressure was again perfect and operating quite normally so we concluded that perhaps the spring had been caught on the housing and stuck open or perhaps some dirt from the crank work had caused the problem and it was now cleared. I decided that we did not need the offered housing and we set off with confidence to Willow Tree.
Next day all went well, so confidence built until half way to Bathurst we again stopped for a tea break. It was time to freak out when on starting up again the oil pressure was down a couple of pounds and proceeded to steadily drop a few pound every 20 K’s until we arrived in Bathurst to visit the Olsen’s in a fine state of concern.
Chris took charge and called up Alan Mitchell in Orange who said “I have one in the shed so stay where you are, I will be there in 40 Minutes” Indeed, it took 42 minutes by which time we had the oil filter assembly removed and on the bench. It was quite clear by now that there was no seat regression as the housing is very robust, so it could only be the spring.
Installing Alan’s old original 1950’s spring brought instant gratification with everything working as normal again and allowing us to do the 4 hour dash to Wagga for our next accommodation without incident.
The car did Tasmania and back to QLD without missing a beat or the oil pressure deviating, which gave me the confidence to pin our woes on a failed T89 spring which was installed during the engine rebuild. The older spring was indeed much more consistent than my one had been as it took into account cold and hot running with the same steady reading. My one always wavered about a bit and gave different readings from cold to hot.
We have since checked a number of used springs and they all show the same wear patterns, which indicate the spring does bow a bit and rub against the housing in 2 places.
Whilst these units have clearly been working for many thousands of miles, I wonder how much wear on the spring is acceptable, so I installed a centre guide just to eliminate any sideways movement and also installed an old spring along with a pressure switch and warning light.
I can only conclude that some after- market springs made, who knows where, might not be quite as good as the original UK manufactured ones and I hope that anyone who experiences this gradual loss of pressure can now proceed to tighten up the adjuster with confidence until a better spring can be fitted. I doubt the spring will fail completely as the dodgy one still has enough tension to operate to complete a journey.
The other conclusion is that we have the most generous and helpful members in our club which makes all our journeys and events such a pleasure.