Re: V8 Cylinder head questions

Posted by Joe Hall On 2014/9/24 20:29:54

Not long ago, I installed a set of heads in the 56J that were rebuilt abut 10 years ago, and included hardened exhaust seats.

I decided to double check everything, but could not find stem height spec either, and decided that was secondary to closed valve spring length anyway (1.750"). I found most of the springs a little too long, with about .090" variance between longest and shortest. I shimmed each as needed, up to .090" in order to get them as close as 1.750" as possible.

For comparison, the old heads, at around 120,000 miles, had closed spring lengths around 1.800-1.850", which I attributed to valve recession.

The "new" heads now have close to 5000 miles on them and all is well, except one of the new Johnson lifters has a light tick that comes and goes at 2100-2500 RPM. I am hoping eventually to isolate it in order to keep from having to replace all 8 lifters on that bank.

In sum, I believe if we forget stem height and just focus on getting closed spring length to around 1.750", all will be OK. Though I suppose, if some bonehead machinist sunk the seats too deep, i.e. .100" or more, the hydraulic lifters could run out of their minimum range and the valves would not close all the way.