Senior Tech Team
Join Date: Aug 2007
Location: The Sunny South
Re: 454 valve keeper fails, but valve not bent?
Update on the mystery valve keeper failure:
Did the cylinder pressure test. I am cautiously optimistic. The valves seem not bent. There is a small amount of airleak, I presume it is past the rings? Anyway, I compared the airleak noise of the suspect cylinder's pressure test to two other cylinders. Sound and minor amount of airflow seems identical in all three. Definitely zero air into the intake. No gas blowing back out of the carb, etc.
Found two bent pushrods on the cylinder in question. The exhaust pushrod was very slightly bent, but the intake pushrod was REALLY bent, up above the guide plate - almost like the valve was incorrectly lashed or something?
I am now questioning my valve lash procedure.
For initial startup I lashed the valves with engine running and rockers clattering, in the usual way. After the initial cam run-in, I relashed the valves following exactly the GM 1966 service manual's instructions for final valve lash on a flat tappet hydraulic cam in an engine that is at operating temperature
The camshaft is a typical "torquer style" hydraulic cam. Sorry, but I don't have the cam sheet (give me a break...it's been 10 years since I bought it, o.k?)
The specs that come to mind are something like .530ish lift and something like 260ish duration. I'm no cam guru, but that does not seem very radical, from my understanding. I bought what was advertised as a typical towing and torque 1500-5000 RPM usable range grind. Again, hydraulic flat tappet cam here.
So, presuming that I didn't screw up the lash order (I didn't, o.k? I was fanatically careful about that) does it seem possible that my valve lash was GROSSLY incorrect? I just don't get how the #2 INTAKE valve bent a pushrod, but not the valve?
I am at a loss. I used GM's recommendation for initial and final lash... paraphrasing my procedure from memory, it is the old:
1. At initial start up, with rocker nuts backed off, run engine with valve covers off. tighten rocker nuts until valve train noise just disappears; reinstall valve covers, then run engine for initial valve train wear-in seating
2. Operate engine for at least 15 minutes, until oil temperature is at operating temperature (VERY IMPORTANT says GM :-)
3. With engine temp stabilized for at least 15 minutes and with each cylinder's cam lobe at base circle in order <using the GM description for how to determine this>, remove rocker covers, loosen the rocker nut until one can spin the pushrod with fingertips.
4. Tighten the nut until the pushrod rotation just gets resistance. This is "ZERO LASH" for a hot engine after initial run in.
5. Then tighten 1 additional turn.
O.K. I cheated and only turned them 1/2 turn...