MG
The Classic Marque

Update: Willie and Ralph, you were both right.
1. The tiny relief hole was clear to 20 thou (poking in s/steel locking wire), but the full hole size seems nearer 35 thou - so it benefited from a re-clean. Anyone know what the intended size of that hole was at manufacture?
2. Once I added much rubber grease to the seal edges etc, the difference was tremendous: careful poking down of the se...

Dont use water even hot water on it JP. Brake fluid IS hydroscopic and it will find every tiny last bit even when you think it is dry! Use a tiny dash of lanolin on it.

Check out and make sure the seal does not foul the breather hole in the reservoir ... per the Y and YT Workshop manual or you will experience limited return of the piston.

And summing up both posts with a question; ---

Will we be shafted by Russia or China first, or Russia and China together?

Mine seems to be like the YA version in the excellent NTG catalogue, Willy; the YB m/c is a different animal as you know.
I'm going to have another go, this time carefully poking down the skirt of that end seal as I ease the piston into the bore - and softening the rubber first with a bit of hot water. I suspect you might be right about the skirt jamming in the bore. Fingers crossed.
John.

JP Hall - have you read the section in the Workshop Manual on Dismantling and Assembling the Master Cylinder page L-3? It is all covered there.

If you do not have a copy of the WSM you can buy it on USB from YZ Publications along with a lot of other Y related manuals! $25US plus shipping - absolute bargain and a must have. Proceeds support the IMGYTR and keep this website subsidized and ...

All back together and ready for a test.But I came in for lunch, to prolong my optimism.

Here's a picture to remind all HIF-types (me included) how many bits and how many beastly connections there are.

This pic----although not MGYA is what i remember a YA m/cyl piston looks like

Hmm
The piston looks different to what i remember as normal
I'm certain they're much more recessed in the centre but having said that it should work.
I think the cup isn't compatable with the piston and just looking at it that cup on the piston appears to have a slightly recessed front edge that allows the sealing edge to jam down on the piston when you poke t in the hole-----maybe a l...

John, have you checked to see if the return hole in the bottom of the reservoir is clear, if this is blocked,or partially blocked,it will stop the piston from returning.Cheers.

I think that's the one, James. I did speak to Burlen, got the reassurance that I was ordering the right one (of three) for my H1 carbs, and the new valve and needle have just arrived - the needle with no damping piston.

Fingers crossed.