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MG MGB Technical - found this when i inspected head

I pulled the head because of car running poorly and thought i had a blown head gasket. Once off the car I started to clean up the head and discovered intake valve on number three cylinder seems to have sunk into head. Can anybody comment on how bad this acually is?
can it still be run, ETC...?

pistolpete

Pete, take all the valves out and inspect them and the seats. It could be low because the valve has been refaced too far, or the seat cut too far, or it has recessed. Unusual for an intake valve to recess itself.
Either way, needs fixing. Probably using a seat insert.
Art Pearse

some newer photos, help all to see it better.

pistolpete

Intake valves don't recede into the head because they don't see the same heat that the exhaust valves do. They are constantly cooled by the intake charge of air and fuel. It looks as if someone got a little too energetic when doing a valve job in the past. I would have hardened seats installed in the intake and exhaust ports. I did this to my head 20 years ago and have had no problems since. Also, the need to adjust the valve clearance seems to have been cut in half with the hardened seats installed. RAY
rjm RAY

Pete. As Ray notes, the solution is relatively simple. But, before spending any money on cylinder head modification, have it inspected for cracks--they are not uncommon.

If the cylinder head is in good condition and shows not cracks, the hardened valve seats that Ray mentions can be fitted, along with new valves. Definitely install hardened seats on all of the exhaust valves as they are the ones which cause the problem with these older cylinder heads originally designed to run on unleaded gasoline.

The intake valves do not require the protection of the hardened seats to the degree that the exhaust valves do. Again, Ray mentions that the intake valves are cooled by the incoming fuel/air mixture. They are, also, closed when the exhaust gasses are being forced out of the cylinder head, unlike the exhaust valve which is open with the hot gasses being forced around it. Hence, you will, definitely, want to use an insert on the intake valve for the number three cylinder, but might not need to have then installed on the other three cylinders.

If funds permit, all new valves and eight hardened seats, on a good crack inspected cylinder head, will give you decades of good performance. If the budget is tight, let your machine shop know and only replace what you absolutely have to. If you have both the time and money available, Peter Burgess performs magic on cylinder heads and his "Econo-Tune" cylinder head is one of the most useful modifications I have seen on a daily driver.

Les
Les Bengtson

As above but the smaller valve is the exhaust - not the inlet!
Chris at Octarine Services

I wonder, could it be a wrong-sized valve? The seat edges appear to still be there.
Regards
Roger
Roger T

I was going to say that too Chris. The recessed valve shown is an exhaust not an inlet. It looks to me like valve seat recession caused by running unleaded fuel.
Mike Howlett

Yes definitely a bad case of valve seat recession. How long have you used unleaded fuel and how was the car driven during that time. It's certainly time for valve seat inserts in the exhausts at least and fit a new set of guides when you are at it. Get the machine shop to cut you three angle seats when they seat the inserts.
Iain MacKintosh

This thread was discussed between 27/04/2010 and 28/04/2010

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