Head Replacement: June 2020

The right head on my 4.3L in my 2000 Chevy S-10 pickup finally decided that enough was enough; these were the original heads.

Valve Stuck Open

In the pic shown to the left, the exhaust valve for the #6 cylinder is stuck open. This valve is the one located at the very bottom of the pic. Notice that the other two exhaust valves are an off-white color while the exhaust valve stuck open is a dark burned color.

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Valve Video

The video shows all the valves operating as the engine is cranked over. The valves for the cylinder in question are the back two. The video shows them to be functioning normally.

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Diagnosis

A power balance revealed a problem with the right bank cylinder 6 and possibly cylinder 4. A compression test showed both cylinders 2 & 4 to have about 160 psi (good compression). However, cylinder 6 had 0 psi. During a cylinder leak down test, I could hear air coming out the tailpipe. When the rocker arm for the exhaust was loosened to allow the valve to fully seat, air still continued to leak out the exhaust valve. If the air leak (heard at tailpipe) would have stopped when the rocker was loosened, then the problem would have been a faulty lifter that wasn't seating all the way.

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Assembly

For the most part, reassembling the upper part of the engine is the reverse of disassembly with a few mentionable notations. First, be sure to use new head bolts if the engine uses torque-to-yield which this 4.3L does. Second, there is a torque sequence to the head bolts that must be followed. Third, the valves on engines with hydraulic lifters such as the ones on this engine are set at zero valve-lash. This means there is no gap when the nuts on the rocker arms are tightened up. These particular rocker arm nuts are torqued to 20 ft-lbs; make sure the valves don't start opening when tightening the rocker arms down. If a valve does start opening then rotating the engine to TDC for that cylinder should help keep it closed. Fourth, in order to set the valves the engine must be rotated so many degrees (57-63 degrees) either before or after TDC of the #1 cylinder. In other words, rotate the timing mark on the balancer (marked with white out in above pics) 57-63 degrees clockwise or counterclockwise away from the other alignment mark and then set the valve lash. It is best do so with the distributor in so that you don't lose engine timing, especially if you need to rotate the engine to TDC of a particular cylinder due to a stubborn valve that won't remain closed.