Induction hardened valve seats (Duke,Joe Lucia?)

[Joe R.]

I have been following the discussion in another thread about a 327/300 rebuild, and I have a question about the induction hardened valve seats that GM apparently started using in 1973 or so.

My question is about the external appearance of the GM heads that have induction hardened seats. Back in 1976 I built a 327/350 using new GM head castings. I recall that a knowledgeable friend recommended a specific GM part number because "it has induction hardened seats." As I recall, these heads had the familiar double-hump casting feature on the ends.

Are the newer head castings with the induction hardened seats externally identical to the ones originally used for a 1967 327/300? If so, what model years or part numbers would qualify?

My 1967 327/300 presently has its original heads, based on the casting numbers and casting dates that are only visible with the valve covers off. However, when the time comes to rebuild the heads (not soon, I hope), it would be tempting to set the originals aside and rebuild another set that has induction hardened seats. I would only consider this if the external appearance of the newer heads was indistinguishable for judging purposes.

I realize that the need for hardened valve seats is highly debatable, and I have already concluded that the risks of installing hardened valve seats outweigh the possible benefits. However, I might consider using newer castings with induction hardened seats as a precaution if there is no downside to doing so.

[Duke W.]

Re: Induction hardened valve seats (Duke,Joe Lucia

I can't help with part numbers/casting numbers of heads with and without induction hardened seats. Induction hardened seats might creat a visual difference - like coloration - but I'm not sure.

You might also be able to get vintage heads induction hardened in the field after seat grinding, but you would have to have faith in the process and technician. A lot of "field procedures" quality can vary vastly more than a OEM processes, which usually have pretty tight control.

I think you're making way to much out of this. If you rebuild your heads with just a good lapped-in valve job, you can dope in some leaded fuel for the first few hundred or few thousand miles as "insurance", then occassionally after that, but if you paid it no attention I don't think you would wear out the seats again unless the car is a daily driver.

Duke

[Joe R.]

Re: Induction hardened valve seats (Duke,Joe Lucia

Thanks Duke. I'm not overly concerned with this issue, since the consenus seems to be that it probably does not matter much. On the other hand, if I have to rebuild my heads anyway and I could easily substitute a set of (possibly used) castings with induction hardened seats, I would consider it. I'm just not sure how to identify suitable castings and I'm not sure whether the difference is detectable during flight judging.

[Clem Z.]

Re: Induction hardened valve seats (Duke,Joe Lucia

the seat area has "blueish" tint to it. color is in the eye of the beholder BUT you can see the color change in the area of the valve seat

[Duke W.]

Re: Induction hardened valve seats (Duke,Joe Lucia

On a used head after you clean up the chamber and ports can you still see the color change from the induction hardening?

Duke

[Mark #28455]

casting marks

Didn't the 1969 and later heads all have accessory bolt holes, so would be an obvious deviation from original? The 041 heads also had a triangular casting mark. The later "double hump" service heads (492 casting?) had accessory bolt holes. I thought the induction hardened factory heads used a 76 cc chamber due to the low compression requirement for unleaded regular, and had a triangular casting mark or a step-like mark.

Mark

[Duke W.]

Good points! *NM*

[Michael H.]

Re: casting marks

Mark,

I believe you are correct on all points. I know that for a few years after the new design 69 heads were released, there was still one old part number for a head that didn't have the 3/8-16 holes/bosses on the ends but I believe that too was discontinued years ago. The induction hardened exh seat began at SOP for 1973 and all of the heads available for these cars had the large chambers.

[Clem Z.]

Re: Induction hardened valve seats (Duke,Joe Lucia

if you refer to "clean up" as polishing the chamber the color change will be gone. it is only on the surface of new heads. the only heads i have seen with this color change are new cast iron BBC open chamber ones and it looks like what you would see if you took a torch and heated it red hot and let it cool which is what happened only they used RF heating. it was done after the seat was machines because the seat itself was discolored

[Duke W.]

Re: Induction hardened valve seats (Duke,Joe Lucia

No, by "cleanup" I was just referring to cleaning deposits off the chamber, seats. and ports by hot tanking or other chemical means that would not disturb the surface mechanically.

My basic question is whether or not one can one determine if a used set of heads have induction hardened seats.

On the BB heads you referred to was the induction hardening done on both seats or just the exhaust seats?

Duke

[Clem Z.]

Re: Induction hardened valve seats (Duke,Joe Lucia

just the exhaust and it was a surface color change and i never noticed it on any other BBC open chamber heads except new ones. the hardness was noticable when i used a valve pocket reamer on the exhaust vs the intake.