Exhaust port

TCap

TCap

Member
Hi everyone. I pulled the exhaust manifold and intake manifold off the engine due to a cracked exhaust manifold. I noticed the #3 cylinder exhaust port on the block is clean while the others have carbon. Not sure why this is. Any ideas? Is it even a problem?
 
#3 doesn't have ignition, or compression..... could also be a slight headgasket leak to a waterjacket so the chamber is "steam cleaned"..... JMHO
 
I've done a compression check and all is ok. I've checked for spark and I know I'm getting spark to the plug. I was afraid it could be a head gasket leak. Is there any other way to check for leak before pulling the head?
 
I'm not surprised by this. IIRC, it is 2 and 3 that tend to have the 'best' combustion. One of the period aftermarket ads supposedly showed the advantage of a particular brand of manifolds (likening it to kerosene lamps out of adjustment which has some parallel basis in fact similarities.)

Still, though why No. 3 and not No. 2 the same. Is No. 2 a bit "lighter" than No. 1 and 4?

I think part of this difference is temperature. When cracks occur they seem to occur mostly on No. 2 and No. 3 valve seats, most frequently on the exhaust. But the temperature (and your hand on the GAV) probably the most direct effect on combustion efficiency.

It may be how you adjust your GAV? Maybe a little heavier on the mix? Too light tends to make for incomplete combustion and heat at the exhaust. But then again, go too rich and you're fighting the two outer cylinders and possibly making them MORE carbonaceous.

I would say if you're not seeing obvious problems with water in the crankcase, or excessive vapor out the exhaust, or bubbles in the cooling water neck then just keep driving it. It will tell you for sure when you've screwed up.

Joe K
 
T Head, If your crack was near that port, maybe enough oxygen got in to help "afterburning" in that port & cleaned it up. Sometimes we worry too much when it's our own car, like, "My car's supposed to NEVER break"! Bill W.
 
just a thought maybe you have a very slight intake gasket leak on #3 which would make that cyl run lean, not enough for an all out misfire but just enough to affect the combustion ratio. i would put it back together and run her and not get all caught up in other scenarios at this point in time....
 
Thanks for all the info guys. The plugs differ in appearance. Currently the 1,2 and 4 plugs are a little on the rich side but look ok (1 is richer than the others...). The #3 is pretty clean, light burn to it but basically looks unused. I'm hoping the cracked exhaust manifold has something to do with it. I will let you guys know what happens after I put the manifolds back on. I did check the valves and everything is working, no sticking.
 
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