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MG MGA - Exhaust Valves 1 and 4

I just pulled the head off my 1600 (am about to replace w/an early B head) and noticed that the exhaust valves for 1 and 4 appear to have led a much hotter life than 2 and 3. 1 and 4 are bright white, the way a plug that has been run too lean would look. Any ideas as to why this is? Since 1 and 2 are fed by the same carb, I don't think this could be a too-lean issue since the exhaust valves for 2 and 3 look fine - dark gray and dry.
My only theory is that 2 and 3 share a siamese exhaust port which might be more volumetically efficient in getting rid of the hot exhaust air, whereas 1 and 4 are on their own.
Is this something I should be concerned about as I install the B head?
thanks in advance
B Phillips

B,
You might have broken compression rings on number one and four pistons, allowing gas/oxygen charged gases to pass into the crankcase causing a lean mixture to fire off. Were you also experiencing crankcase pressure/blowby from the valve cover filler cap?

On my MKII, # 1 cylinder had low compression (50lbs), all other pistons were about 150 lbs. In number one cylinder, the three compression rings were totally gone. The longest piece of compresssoin ring was 2/3 inch long. Most pieces were about 1/8 inch long. The exhaust valve on number 1 cylinder was white compared with the other the three exhaust valves.

I pulled number one piston to convince myself it was the compression rings instead of the head gasket. The compresion rings just fell out as I pushed number one piston up and out of the cylinder.

Good luck,
Ray
Ray Ammeter

It's the siamese intake ports, not the exhaust, that make 1 and 4 leaner than 2 and 3. almost all four cylinders use a 1-3-4-2 firing order. Cut another way, that is 2-1-3-4. You get a "bang" every 180 degrees of crank angle. For each port, the "outside" cylinder filltime is 1/3 as long it's "inside" partner. 1 and 4 fill for 180 degrees while 2 and 3 fill for 540 degrees.

Fuel/air flow in a "wet" manifold so the real-world difference is less than the numbers apply. Still, 1 and 4 always run leaner.

Another tuning complication is "modern" fuel. It leaves fewer deposits than older fuel. I tune 1 and 4 to "tan-tinted"- not white but short of the classic light tan. At this setting, 2 and 3 are tan and I need to pull the choke for cold starts. Overall, a bit rich is better than a bit lean.

Hope this helps.
Bill
Bill Eastman

Ray and Bill, thanks for your input. I did a compresion test just before I pulled the old head; numbers 1 and 4 actually yielded the best nunmbers!
B Phillips

This thread was discussed between 14/01/2007 and 16/01/2007

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