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MG MG Y Type - SU Dash Pot Oil

Which oil is best suited to use in the SU dash pot .I have various recommendations
Penrite
3-in-One multi purpose Oil
20/50 engine oil
ATF (automatic transmission fluid )
Mobil 1 15/50 motorcycle oil

I have been using the 20/50 engine oil .

Ed Winters
E Winters

Hi Ed,
Out of your choices, I would suggest 3 in one. Historically I always used Singer Sewing Machine Oil but have not see this around for many years. Possibly it is still available?
Paul
P M Grafham

The function of the oil is to dampen the upwards movement of the piston when accelerating.

The thicker the oil, the richer the mixture under acceleration, the faster the reaction to the throttle.
The thinner the oil, the weaker the mixture under acceleration, the more economic the car.

What follows from above is that the right oil choice also depends on what you expect from the car. For our sedate Y's, maybe even a thinner oil like a 10/40 multigrade could be the best choice.

The experiment is all yours I'd say?
Willem van der Veer

SU carb specialists Burlen sell dash pot oil.
Richard
R E Knight

For the last 10 years I have used 10 grade motorcycle fork oil. Comes in reasonable bottle size/price and works perfectly !.

As Willem says, if you want to adjust what suits you, vary the grade 5,10,15,20 are all available.

Happy Days

Tony
A L SLATTERY

Not only the grade effects the acceleration but I find that in slow moving traffic no oil in the dash pot causes surging or jerking on slow take up. The Stromburg fitted to my Ford Anglia with much softer engine mounts becomes a real problem in pulling away. I find just engine oil 20/50 on both Y and 105e seems right for my style of driving Bryan
B Mellem

Bryan,

With no oil at all in the damper, the surging or jerking is caused by the weak mixture on opening the throttle.
Other carburetors than the SU/Stromberg solve this problem with an acceleration pump.

The SU varies it's venturi with the piston reacting to the under pressure in the engine. The dampened movement of the piston causes a smaller venturi at a greater under pressure, causing the air going through the venturi to speed up and suck in more petrol than at a constant speed. Therefore the SU doesn't need an acceleration pump and is a very ingenious device through it's simplicity.
Willem van der Veer

The point I was making was as an extreme example of the effects of various grades of damping fluid starting from none, and was hypothetical. In my opinion the grade used in the carb dash pot depends largely on the dynamics of the car mass, the clutch operation, transmission tolerances, and smooth reaction. I just suggest its a matter of personal preference, sort of 'suck it and see' Bryan
B Mellem

The reason I bought up the topic about dash pot oil was because I have recently had my MG B tuned by a very reputable expert and he insisted that ATF ( automatic transmission fluid ) to be the best .
On my internet research I found all the recommendations as on my first post .
So my interest in finding out what the Y fraternity suggest as the most suitable dash pot oil .
E Winters

Very missleading for new y owners all these difffernt grades being quoted, your workshop manual and su burlen clearly state SINGLE grade 20sae oil is the correct oil to use
John mg0362 or in english UMG624
JC Jebb

When you think about it, maybe a single grade is the best solution.
When cold it will be thicker, providing some form of extra choke function that isn't needed in a warm engine.

I do seem to recall that in the factory special tuning booklets thicker oil was mentioned, maybe I'll do a search today to soften the 'very misleading'.
Willem van der Veer

Sorry John if you think I spread misinformation but in contrast to modern times where electronic ignition fires exactly and injectors always give the correct fuel air ratio our MG Ys stem from a time when things were more empirical. The ignition wears and is always slightly changing, the carburation varies with temperature and humidity, the butterfly shaft lets in air. I can go on at great length regarding the differences between one car of the same make and another, as I say what is fine for one may not work for another. Bryan
B Mellem

Having been driving and motorcycling since the early 1950s I can reliably confirm that multi grade oil was not available when the Y was produced and only in the mid 50s when visco static came on the market. In fact you carried out an oil change to thin grade in the Autumn and thick grade at about Easter when the annual decoke was carried out, and so the dash pot oil was changed as well. In fact some manufactures advised that the gearbox and diff oil be changed. I remember in very cold weather it became almost impossible to change gear until the oil warmed up. That is why many drivers stored their cars off the road during the winter months and saved on the road tax. It is quite impossible to compare motoring from then to now. It was a different world and I will say a different people. Bryan
B Mellem

Optimum damping is not just a result of the right oil. The damper pistons can vary a lot too. I have tried several different pistons (including new ones) in my s/c TC carby and the damping effect varied from light to heavy! A new piston did not have the heaviest effect! I don't know if pistons are all meant to be the same, but they certainly are not.

When I fitted the supercharger in the mid 70s, I used engine oil in the carby but still had to GENTLY increase throttle when accelerating, to prevent the engine from dying. Despite the heavy oil, there was not enough damping. When I fitted another piston, which had more damping effect, The problem disappeared.

Bob Schapel
R L Schapel

Liquimatic DII is an automatic transmission fluid blended from highly refined mineral oils and a high performance additive system. It is designed to meet the performance requirements of General Motors DexronŽ

This ATF has among its applications ,motor cycle fork oil so could it be suitable for use in the Jackel system and also the SU carb .

Ed
E Winters

This thread was discussed between 03/08/2016 and 08/08/2016

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