I recently replaced the valve seals in my ’91 Formula (5.7L). I used compressed air to hold the valves in place. Everything worked good until I got to the #3 cylinder. When I applied air pressure to the cylinder you could hear the air rushing out of the cylinder. The air compressor could hardly keep up and the air was coming out the exhaust pipes. I assume this means that for some reason or another, the exhaust valve is not properly seating? I would think if it was rings, the air would come out of the crankcase, if it was head gasket, the two adjacent cylinders would have done the same thing or at least acted differently. I guess I was to be sure that’s the problem before I take the head off on that side and get an idea about what it will take to fix the problem before I tear into it. Also, can you test compression on the #3 cylinder without removing all the other plugs? I would like to check the compression of #1, 3 & 5, but don’t want to take out plugs #6 or 8!!! Any help would be greatly appreciated. Thanks.

-Chris

 

chris, you hit the nail on the head. you have a bad exhaust valve, or seat. assuming the rocker arm pressure is relieved, the only way for pressure to escape through the exhaust is by the valve

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85 IROC 350 11:1keith blacks,.555lift erson roller cam,1.5 crane roller rockers,edelbrock intake,holley 4150 750dbl pumper, nitrous oxide,full length heddman headers,true dual exhaust, 11"stall converter, 700R4, 3.73 locker