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MG Midget and Sprite Technical - Valve seat crack ?

Further the unleaded cyl head thread below...

having decided to just get it functional myself and get it all back in pending Konversion. I now found a small crack in one of the inlet valve seats whilst lapping the valves in.

The engine is a 1500cc and the crack is small one right actually in the seat sealing area - doesn't appear to go into the chamber surface or valve port as far as I can see. Its on the ouside facing away from the valve bridge..

My plan was to clean it up and lap in the valve and live with it..
Any one any experience or knowledge of craking in this area on this head and what consequence may be .?

I will try for picture - but its so small and my camera doesn't have macro lens...
John Barber

Not good. Following is specific to MGB but is an excellent tutorial:

http://www.flowspeed.com/cracked.htm

FRM
FR Millmore

So what sort of mileage would you expect to do on this engine before the K goes in?

Probably quicker and easier just to buy a replacement head off ebay

Guy

Hairline crack in inlet seat is ok as it will not burn away. Hairline crack on ex seat bad as it will burn away. Solution insert for ex seat and weld it in situ if crack goes across to inlet seat. Not seen an inlet seat crack propogate after this treatment.

Peter
Peter Burgess Tuning

Interesting the crack I have looks like the ones in the third picture in the sequence which is on two exh seats. The crack I have doesn't go beyond the seat contact area as far as I can see. So it looks as though machining and fitting an insert could fix it. However I didn't want to spend anything on this engine as its coming out in a year or so.

Do you think it would last - and whats the worse that can happen..

Water leaks into the chamber ? and pressurised coolant circuit if the comb gases get through to the coolant circuit I guess.

For the moment the crack doesn't look big enough to extend through - so its a question of it lasting long enough.. However it my then be junk when I am finished...
John Barber

I must have been typing when you were Peter.

I have just realised the crack is on the small valve which is exhaust side ! the worse of the two options...

how long would it last do you think ?
John Barber

It will most likely just get bigger and burn the seat and valve out. Could get through to a water jacket, but will be noticeable well before that happens.

Peter -
Are you saying to weld the insert in to keep it from falling out, because of a still present crack? Or put the insert in, then weld the rest of the crack and the insert?
Either way, seems to me that welding on the insert is a sure way to make it loose, as Sean does for removal.

FRM
FR Millmore

Hiya

On CI heads we weld the insert in not on the crack area and from insert to valve throat (bowl) and only a small spot of weld. No heat build up or denaturing of the head or insert. We do not weld cracks. We weld the insert in purely as a precautionary measure. If the crack is severe we insert inlet seat too, if we are able to as some heads will not take both inserts.

Peter
Peter Burgess Tuning

This thread was discussed between 02/03/2012 and 03/03/2012

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