Oil Circuit Improvement

(a tip from France by Laurent Castel)

The first check after starting the engine of my TD is the oil pressure gauge. I used to have a very anguished long few seconds before the pressure rises above zero.

During these long seconds I suffered as much as my engine.

This agonising is over with the modification described hereafter.

Modern spin on filters often include a check valve which prevents the circuit from draining when the engine stops. T-Typers who are using the conversion kit take benefit of this valve.

But how anachronistic is this modern filter in the engine compartment!

This article offers a solution which keeps the period appearance of the filter by fitting an additional check valve in the oil circuit. Furthermore, the check valve, upstream of the filter and the pump, prevents the filter and the pump from draining.

Modern engines are also sometimes equipped with one or several check valves at suitable locations in the engine to get immediate pressure on bearings.

For the XPAG, there is one location which is easy to access and efficient.

The pipe between the oil strainer and the sump is the right place to implement the check valve. It is upstream of the pump and upstream of the filter. Therefore, only a short length of the pipe is prone to immediate draining instead of the entire engine and filter. The sump is easily removed without getting the entire engine out of the car.

I bought a ball type check valve with a Teflon seat. According to the local dealer, the valve is oil proof and high temperature resistant. No problem is foreseen for the oil pressure circuit. Actually, mine is installed since November 2014 with no issue. More than 1000 miles.

One very important criterion when choosing the valve is the very low tension of the spring. Some low price items are very strong and would need a too high suction to open. Choose a model with a spring so light that you cannot even feel it when pushing the ball. Good quality valves always feature that low pressure forward threshold.

I cut twice the horizontal part of the pipe and removed the corresponding length to insert the check valve. Then I had the threaded end pieces welded on both parts of the pipe. The valve had to be lightly ground at both ends to get enough clearance with the sump wall. Threaded parts are smeared with a sealing compound and the valve is then tightened until the original length is reached. I guess, usual plumbing Teflon strip might also be used. Double check the forward direction of the check valve indicated by an arrow on it. The arrow shall indicate the sump flange. Take the opportunity to clean the strainer. Install the whole assembly back in the sump with a new gasket between the flange and the sump wall. Sealing compound on the engine side of the gasket is an additional precaution.

The results are amazing!

When leaving the car parked for more than a night, the time to get pressure used to be about 10 seconds. With the check valve installed, this time is now reduced to 2 seconds, even when parked for one month. When parking for a few hours, I often get the pressure at first starter revolutions, before first explosion.

The XPAG will never dry and thanks you for it!

Ed’s note: Laurent’s car (TD29133) was originally registered in Birmingham. He has been keen to find out the history of his TD and his patience was rewarded when he was contacted by a previous custodian who owned the car from 1969 through to 1984. Laurent now has dates for engine and body rebuilds, together with mileages (it’s been established that the car has done 113,000 miles). The previous custodian also has lots of photos, the log book, instruction manual and still has some spare parts! A good result and it’s heartening to know that there are previous owners out there who take the trouble to help.

5 thoughts on “Oil Circuit Improvement

  1. Peter Jones says:

    Seems to be just the thing for my 18/80 too⎯here the pressure can take up to half a minute to move the needle at all !

  2. Damian Rowe says:

    There is a very small check valve we use in autoclaves with a stainless ball and a 1/8 BSP M-Fthread. Not sure without looking, but I wonder if it could be fitted into the suction pipe, right down in the pickup strainer. A short fitting could be brazed on inside the ‘cup’ part. They are a springless one that uses gravity to seal the ball. Will have to pull one apart to see what the seat is, but they handle steam at 135 C so cant be bad. Could also be fitted in the pipe to the head etc. Only about 25 mm long.

  3. Mike says:

    An interesting modification. I was told some years ago and have always followed this advice; after any longish period of engine inactivity,(overnight for example), turn the engine over without the ignition on until the OPG registers oil pressure, and then start it.

    • Steve Ball says:

      What a brilliant article, Laurent. Who knows how much engine wear will be saved by this idea? Merci bien!

      This reminds me of the series of factory modifications throughout XPAG/XPAW development that were intended to get the oil pump to prime after an oil change.

      Quoting Neil Cairns…

      ‘So at SC2/17670 and TD2/20972 the oil pump gained a priming plug. You could fill up the oil pump, and get oil pressure and not a heart attack!’

      Does anyone know what this filler plug looks like and could post a picture; even ideally a with and without picture? I would want to use it at every oil change on relevant cars .

      ‘At last, by drilling a small air hole up inside the oil pump, the oil pump was made self-priming. This was at TF/31263 and XPAW/5142. Changing the oil was no problem, oil pressure was instant on starting up afterwards.’

      Again this sounds like an important retro-mod worth doing at an engine rebuild but does anyone have a reliable drawing to allow us to get the Black and Decker out?

      The changes are here in Neil Cairns’ excellent article.

      The relevant items are XPAG mods 20, 25 and 30 but there are many other improvements mentioned that will be missing on many engines such as sump baffles to prevent damaging oil surge. Probably worth a read.

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