455 with Tuliped Valves

[brauzac]

Hi guys, hoping I can get some assistance with my 1972 Olds 455 big block. I recently had my engine rebuilt.. all stock except .60 over pistons and an RV cam (motor home application) during our 1st trip out and approximately 200 miles the engine lost power under medium load (incline) when we did a compression check, it had low readings in cylinders 2 (70psi) and cylinder 4 (130 psi) all other cylinders were good at 155 +/- 2psi. We pulled the heads and sent them back to the machine shop (no indication of blown head gasket anywhere) the machinist stated we had Tuliped valves on those cylinders. Here's where in stumped. The entire cooling system is new and oversized, cooling fans draw a serious amount of air and are completely shrouded new analog temp gauge read 205 deg when power was lost. Temp range stayed between 185 and 210. The spark is controlled by HEI distributor (new) and initial timing was 10 deg @1100 rpm. Total timing is set at 32 deg, spark plug gap is .045, We are using ported vacuum and have an new edelbrock 750 to boot. Fuel pressure is a steady 5.5 psi. Any assistance is greatly appreciated to determine what caused the cylinders to get hot enough to tulip the valves.


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[rcull]

The problem is heat as you probably already know. There could be many possible causes, here is an article outlining some: https://www.ms-motorservice.com/en/technipedia/post/valve-damage-and-causes/

You mention that it did run as hot as 210, which while not usually excessive, could be enough on a new motor where surfaces have not seated in well.

You could look at the valve seat, is it wide enough. While it is new, it may not make a real good contact and not move heat as well as it could a few miles down the road.

Most shops simply ream valve guides to fit, the heat does not transfer quite as well until a few miles have worn them to better contact surfaces.