MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

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 Midget and Sprite Technical - valve guide replacement

Ok - so in a ham-fisted attempt to remove a stuck valve I've managed to break the top of the valve guide. Any recommendations on where to get a replacement fitted in the Christchurch / Bournemouth / Poole area?

I'm assuming the guide will need reaming and the seat re-cutting.

Thanks

Bob
Rob Storer

Best recommendation I can think of is to parcel the whole head up and send it to Peter Burgess.
Doesn't cost as much as you might think and totally worry free.
Greybeard

Thanks Greybeard, will give them a call and get a price.
Rob Storer

You could have a go at it yourself, especially if it's just one. You can buy guide drifts on ebay which should work ok with a bit of care and putting them in is easy enough. I've done a few recently and they didn't need the seats re cutting just a good grinding in. The A series ones I've done didn't need reaming, my Triumph motorbike ones did but I just used a Flex Hone in my drill and it worked fine.


John Payne

My experience is like John's. I've fitted a few sets of the standard cast iron guides and they didn't need reaming after fitting but it was a few years ago so what the quality (accuracy) is like now I don't know. Best if you can get a drift and use a press rather than hammering them in/out and useful to have a collar around the guide to set the guide height above the spring seat, the pressing in drift should be larger to stop against the collar. Don't know if they're available on ebay but easy enough to machine all required if you have a lathe or access to one or a mate with one. IIRC the guide height above spring seat is detailed in Vizard and maybe elsewhere and differs between small bore and large bore heads. Not sure about the need to lap or re-cut the seats as I have seat cutters so skimmed the 3 angles after fitting the guides.
David Billington

Thanks for all the advice. I was tempted to have a go myself but managed to find a local engineering shop that will fit a new guide, valve and recut the seat for a very reasonable price. Dropped the head off this morning, fingers crossed they'll do a good job.

Thanks again

Bob
Rob Storer

For anyone else reading this, I thought I'd share my method. Knocking the guide out is easy enough, using a drift turned down to pilot the inside of the guide. It should really be a hardened drift but I was too lazy to do that so used ordinary mild steel. You need a lump hammer to get the guide to move, knocking it from above into the chamber. The top of the drift splays out with the hammer blows but it will last long enough for one or two heads.

The official workshop manual says to drift the new guide in using the same tool. Do not do this - there is a high risk of cracking the guide. I usually put mine in the freezer and warm up the head so they are not quite as tight. I use a big bench vice to press them in. I made a short sleeve to go over the guide to act as a stop, and the same drift with a washer between the two. You do need to tap the guide in gently to get it started, before the full pressing job. Even with all this care, one of the guides ended up with a hairline crack and had to be replaced. Bronze guides will take a lot more abuse of course.

I happened to have a 9/31" reamer lying around so all guides are reamed to the correct size. I have recut the seats and checked them with marking blue.

Les
L B Rose

This thread was discussed between 05/01/2020 and 09/01/2020

MG Midget and Sprite Technical index

This thread is from the archives. Join the live MG Midget and Sprite Technical BBS now