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MG MGB Technical - Inlet/Exhaust valves

This may seem like a very strange question but can you use an inlet valve from the 1500 head as an exhaust valve in the 1800 head? They are both the same diameter and the inlet valve will lap into the exhaust seat, but are they made from different materials.

The reason I ask is that my 1800 exhaust valves are stuffed and I have a set of 1500 inlets that are in excellent condition. I borrowed a valve seat cutter from a local servo so the seats are now excellent.

Cheers
Tony
Tony Oliver

Tony,
The inlet valves are probably made from a medium-carbon, low-alloy steel, whereas the exhaust valves are made from a high-alloy steel which is resistant to oxidation at high temperatures.
The stems of the exhaust valves would be a similar material to the inlet valve.
I suspect that you would have a very short valve life if you were to use the inlets as exhausts.

Regards,
David
David Overington

Thanks David. I was hoping to save $50 to 60 by not getting new valves. The old one are so badly pitted they would need re-facing, and they are only 12 months and 6000 Kms old. Something bad must be happening inside the motor.

Tony
Tony Oliver

Tony
If there is still plenty of material there which you would expect there would be on valves that have only traveled such a short distance I would get them refaced.
The usual cause of seat failure at low mileage is soft valve springs. You need to get them measured up on a spring checker and make sure the stack height is correct when assembling the head. Don't use inlet valves as exhaust valves-- they will burn out the first time you put them under pressure,if they get that far. Cheers Willy.
WilliamRevit

Tony do you have a piccie of the pitting? Valve set on valves suffer from carbon indentation until all the dents join up, is this what is showing? Especially when leadfree inserts are fitted.

Peter
peter burgess

No way can you use inlet valves as exhausts. Exhaust valves are made of stellite and capable of withstanding extremes of temperatures which inlets are not. In any event an exhaist valve has a 45 degree seat whilst an inlet has a 30 degree seat.
Iain MacKintosh

Thanks Gents. My camera is not really very good but I will try for a picture. I'll get the springs checked as well. I have not had hardened seats fitted

Iain. Mine is a '67 model so it may be different but all my valve seats are 45 degrees (45.5 to be precise according to the manual).

Tony
Tony Oliver

This thread was discussed between 28/10/2008 and 31/10/2008

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