Packard Forum Index » V-8 (1955-56)

In going over my 352 heads that were rebuilt, I may have some of the intake seats touched up due to the way the valves contact the heads. This got me to thinking, is there a spec for valve stem height when the seats/ valves are ground? My engine guy is unlikely to have this measurement for a Packard.
Also, what is the likelihood of hitting water when installing hardened exhaust seat inserts. One of my "consultants" is worried about this.
Lastly, has anyone ever flow tested these heads with the Exhaust port crossovers on #s 3&5 and #s 4&6 filed w/ Aluminum and reshaped? This is worth a gain on Olds & Pontiac V8s, though I will not be pursuing this on my engine.
Just wondering in case of HP applications.
Thank You Gentlemen.

Forget the hardened seats unless u're running aluminium heads or plan sustained high rpm under extreme heat conditions. Doesn't matter even if running ss valves. SS valves in my 56 Exec and 25k+++ miles no problems. No hardened seats. routinely run in middle tn. at 70+ mph.

Quote:If he's a member of AERA, he'd have access to PROSIS and that has the stem height dimension.

Quote:

Yes, if one builds a high-rise single-plane intake manifold, uses a long-duration racing cam and builds four-tube headers, then filling the exhaust crossover will show slight gains in horsepower.

jack vines

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.

Seems to me that is way too much to be attributable just to valve seat recession, perhaps the valve faces were refaced one or more times as well which would add to the difference.

The hydraulic lifters have .250" travel, so they won't usually be the the problem.

As mentioned, if the seats are cut and the valves are refaced, then the net assembled result can be too little spring pressure. The spring height measurement is just a way for the guy on the assembly bench to make sure he's putting back in enough spring pressure.

If several shims are required, then sometimes it's necessary to grind the valve tip to get stem height correct. But that doesn't take into account if the camshaft lobes and/or rocker tips have been reground, block and/or heads decked. It's a multi-variable regression analysis.

jack vines

Here are a couple of notes for future reference: The springs I used were BBC springs, Sealed Power # VS 657. They are smaller in dia so the valve guide bosses had to be machined & the shop charged me $120 for that. The smaller spring required new retainers and that part was Comp Cams # 744-16.
The benefits are stronger and easy to source springs and hardened retainers. From vendors, new springs & factory keepers seemed to be a little more than $200 and my cost here was around $240.

Possible to machine only the BBC retainers to fit the Packard springs?????

Hi V8, actually the BBC springs are a little smaller diameter so you would need to add to the BBC retainer to fit the Packard spring. I understood that the factory setup was uniquely sized making mixing & matching difficult.
Just think of what Packard lifters would cost if Mopar parts did not fit!