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MG MG Y Type - YA Carb Piston

I've stripped down and refurbished the carb, with no problems - I employed the old tactic of having a duplicate spare next to the "real" one on the bench to help keep track of tiny seals, retainers etc.
One question emerged : my YA came with a fairly heavy brass piston, still in lovely condition; but the spare, identical but of unknown origin, has a much lighter aluminium piston. Is either "correct", and what would be the relative merits of one over the other?? With thanks, John.
J P Hall

Ithink the brass piston is correct, that is, my 1950 Y also has it.

I have some spare aluminium pistons too, but these are used with a spring or a heavy iron(?) ring. The brass ones are earlier I would think.
Willem van der Veer

Hi John,
Have you read the SU Data Sheets in the Technical Data section of the IMGYTR website ?. Do the pistons have a part number perhaps ?. If you want to compare weights - I can do the same. William is correct - the light alloy pistons have return springs, the heavier brass or steel weighted pistons do not have return springs.

It would be nice if our cars had the original parts, but sometimes you have to make do with what you can get to keep it on the road.

Sounds like you are getting close to driving the YA again ?. Safety Fast

Tony
A L SLATTERY

Brass Piston John if you are using all the other original fittings!

Paul
Paul Barrow

Thanks all. I read that the brass piston, which is a beautiful piece, was found commonly on earlier (30s and 40s) Morrii, but was superseded probably for reasons of cost, by the aluminium version with spring pressure to replace gravity/weight. Both should do the job; but I must admit that the close fit and vacuum pressure is superior (in my particular dashpot) with the lighter ally piston. I'll have to buy a spring.

Tony, only close if you count completion of the mechanicals, running gear etc on the chassis to "test fire" stage. I'm just now looking to see if anyone has put down a basic guide to rigging up fuel, ignition, temporary oil pressure gauge and whatever else is useful. I can figure it out, but always happy to learn from the experience of others who have been there before me.
Just for fun, I will weigh the two piston specimens tomorrow at work. Will post for info.
Kind regards, John.
J P Hall

Update on weights of the 2 pistons : aluminium w/o needle: 100gms; brass with needle attached : 240gms.Probably take off 4 gms for needle. John.
J P Hall

This thread was discussed between 23/05/2015 and 26/05/2015

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