Don:

Another car racer. My goodness. Then you know that after the rockers wear a little bit the feeler clearance is less than the real clearance. And the only accurate way to set valves is with a dial gauge. And that rocker wear is why I say to use the 0.0015" thickness, if you insist on using a feeler.

I have not used a feeler on a push rod engine for a very long time, except for instruction or demonstration. I have a P&G Valve Gapper that has served me admirably for more than 40 years now.

I was racing Triumph cars when I got it, and I got it at the recommendation of a fellow named Rob Walker. If you have followed GP racing, Rob had his own private GP racing outfit. What's more, I bought mine from Rob. More likely you will remember Jo Siffert. Jo was Rob's principal driver, when he was killed Rob gave up racing.

Anyway. On the model four strokes it is impossible to have the valves too tight and start the engine. At zero clearance they will still seal when cold, and you will have the greatest duration possible, and also the greatest power. I've never seen the tight adjustment hurt the idle, but I have picked up rpm on the top end by setting them tight. And there is less hammering in the valve gear with a tight adjustment, and therefore the least wear.

Bill.