MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Weird SU Carb Piston

Had a little surprise this week when dismantling an SU H4 carb for a rebuild, and discovered a piston type not ever encountered previously. They don't have the normal vacuum passages, but do have a small hole in the side of the uppermost barrel. I regurgitaed an old thread over on MG Experience, but couldn't advance my search for its origins, and this is a reply I received to my enquiry to SU Burlens recently.

"Hi Mr Prior
These sort of pistons do not require a spring , they are termed as a weighted piston from an earlier design , then changed to the spring type which was more flexible in it’s range of uses , if the piston is tight it may not be in it’s original body as people do tend to muck about with these things . Piston and chambers are matched at the time of production to achieve the 3 to 5 second drop rate that was acceptable"

They haven't told me to which car it belongs and I am reluctant to re-use them so, I will have to put them aside until more is unearthed. Perhaps someone here has some information on them?

Maurie P






R M Prior

Hi Maurie
Did that piston have a donut weight on top of it--
They're called a weighted piston and were early pre-springed version and were used up to mid/late 60's- some real early minis still had them
Some earlier ones were brass-for weight then alloy as is yours and depending on what sized engine they were fitted to, some had a donut weight to act as a retarder, same as the later springed versions use different grade springs to adjust for engine size.
The old racer trick used to be to dig the weights out and turf them so the pistons opened up quicker--only for angry engines though-

Cheers
willy
William Revit

This thread was discussed on 01/10/2022

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.