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MG Midget and Sprite Technical - Valve stem seals [again...]

Lots of smoke so just spent the afternoon taking off the head to have a look. I found that two of the "top-hat" style valve stem seals had shed their small tensioning springs, effectively stopping them behaving as "seals". One in each pair of inlet valves meant that the whole head was a mess of oil with pools on the tops of the pistons. Any one else had this experience, or found a good source of reliable seals? Thanks as ever.
Dave
David Cox

you took the head off....sorry to hear that, there are seveal options for replacing the seals without removing the head.

1st the most common that I have trouble trusting...fill the cly with compressed air, this will hold the valves shut

2.nd fill the clyinder with rope thur the spark plug hole, so the valves cant fall

3rd. rotate the piston to the top of each clyinder as you replace the top hat

4th tie a long piece of string to the valve and hold it up


me I do a combination of 3 and 4, but Ive only done this 3-4 times


I only had problrms with top hats when I purchased the car...not sence, the ones that come in a "payen" upper gasket kit seem to be pretty good....Being that you will NOW need a new head gasket. You cant beat the Payen kit...So Id try that, it comes with all the gaskets needed, and the top hates

Prop
Props Black Hole

I find removing the cylinder head by far and away the very easiest method to do stem seals.

Prop you will have to help me with this, I have tried the compressed air method and yes that holds the valve into its seat very well, however the problem I have with these methods is actually compressing the spring to release the collets!!! How have you managed that?
Secondly your string method for holding the valve up (not the rope in the cylinder) how do you fix this to the top of the valve whilst releasing the retaining collets?
Robert (Bob) Midget Turbo

Robert,
I have removed valve springs and replaced stem seals using rope inside the cylinder. To compress the springs I have what looks like a home made tool that someone gave me about 40 years ago. Shaped a bit like a tuning fork it is meant to hook under the rocker shaft and then you lever down on the spring cap enough to remove the collets. It works, but is a bit tricky to use as I don't think it was made particularly for A series engines and can slip off to one side if one isn't careful;.

I also just don't understand how one could tie a bit of string to the valve to hold it up whilst removing or re-fitting springs and collets!
Guy Weller

Guy,

The tool you describe sounds like that intended for FIAT/Lancia twin cams, work s very well for those engines. For A series I've used various including ones knocked up from plumbing fittings and gripped in a vice.
David Billington

all very interesting chaps but what about the seals??
David Cox

David,
It was given to me by an old chap who lived near Perranporth in around 1968 when I had an Austin 7 special. I had put a con=rod through the side of the crank case and he had various engines and parts that he let me go through for spares. Although the 7 was a side valve engine he was having a clear out and gave me load of old tools that he had, some from before the war.

David: The normal top hat seals with the little spring thing from the Payen kits seem to work well enough for me. But I do remember reading about some who have fitted ceramic seals. No idea what from though.

Guy
Guy Weller

KD make a tool for that specific purpose.. It has two legs that go into the coils at the bottom of the spring and then a screw top that straddles the to washer. then you remove the collets lift the complete compressed spring up-replace the top hat seal and reinstall the spring and collets. Unscrew the top and it will be back as before. Make certain that you use rope inserted inside the cylinder or you will drop a valve.
Sandy
SANDY SANDERS

The string trick is my own...a bit fiddly, run the string thur the springs off to the side, make a slip knot and chinch it down above the top hat, I use an old pair of spring pliars for doing B&S lawn mowers...looks like a tuning fork but has wide blades to catch both inner and outer springs...compress the spring remove the 2 collet pieces then the spring retainer, pull the springs off and the old top hat Off the string hold the string up...It may slip and catch at the top of the stem thats cool...hold valve remove string, put new top hat back on, put string back on fish string thur sides of springs...reassemble...use exacto knife to cut off string from valve stem...Done

Granted Ive never done it on the midget, just the toyota and mazda truck, but I dont see why it cant be done on the A-series


Prop
Props Black Hole

This thread was discussed between 06/09/2009 and 07/09/2009

MG Midget and Sprite Technical index

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