Thread: Chevy 350, zero compression. engine not starting

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Originally Posted by jerry clayton

I think you said he installed bigger springs-----------well as other things have showed up, I'm wandering if the rockers will even clear those retainers underneath side-- I would suggest that yu get a vortec vavle and compare the tip length to the ones in your heads. vortec valve tips were longer for the alignment dealie with the rockers------

JbRat, Jerry makes a valid point here. When you get the proper rockers installed, roll the motor over with a breaker bar/socket and inspect each and every rocker tip for missing the top of the retainer. If the side of the rocker that hangs down over the valve tip contacts the surface of the retainer, the ball game is over because the locks will be loaded/unloaded, loaded/unloaded, loaded/unloaded until they fail and you drop a valve or 3, resulting in destroyed pistons and cylinder walls and probably the heads as well. Have a buddy do the turning while you slide a small piece of plastic between the rocker rail and the retainer. I have measured the thickness of a plastic coffee can lid at 0.023" (twenty three thousandths of an inch), so cutting two of these pieces from a lid to slide between each rocker and retainer (one on each side of the rocker) will prove at least 0.023" clearance and that should be plenty. I'm visualizing the strips at maybe 1/2" wide, by 4" long. This will take some patience, so don't get in a hurry. There is a word that describes this checking and re-checking of parts for a specified clearance, it's called blueprinting. I'll bet that somewhere in the blueprints of the L31 heads, you could find the exact figure that the Chevrolet engineers specified for rocker to retainer clearance, but lacking that information, I'm of the opinion that ~0.020"/0.025" would be sufficient. The old saying is that a miss is as good as a mile, but taking clearance measurements with the motor sitting static is a whole lot different than taking clearance measurements with the crank twisting 5 grand or better.

If there is insufficient clearance, then you will need to change to longer valves made specifically for L31 heads or use locks that have the internal lip moved up in the lock to move the retainer down in relation to the tip of the valve. These are called plus 0.050" or minus 0.050" locks. Caution though, while using a minus lock gives more valve stem sticking up beyond the retainer, it also reduces the valve spring installed height and could contribute to valve spring coil bind, which usually results in bent or broken pushrods, but in extreme cases, could do mechanical damage to the lifters/camshaft if stout pushrods were used or if your personal kharma is S.O.L., or the increased valve spring pressure could take a toll on the lifter/lobe interface and roach the cam (actually the lifter goes away first, then takes out the lobe).

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