1956 hardened seats?

[Lexi]

I am currently in the midst of having a 1956 365 Cadillac engine rebuilt. The re-builder does not believe the engine had been torn down in the past. While showing me the cylinder heads he stated that he saw evidence of the valve seats having been "flame hardened" by the factory. I was not aware that GM did this back in 1956. Because it is a Cadillac did GM perhaps engage in some sort of valve hardening process with these engines when new? That would be news to me. Would appreciate any input on this. Clay/Lexi

[Dave Shepherd]

Could be, seems unusual though.  The exhaust valve seat is the more common issue when running modern gas, was supposed to cause seat recession,, but I have never personally seen this happen.  I do know  early Chrysler Hemis had replaceable hardened exhaust seats.

[Lexi]

Of note is that these heads are the "2nd generation" ones from that year. Perhaps GM added this to the manufacturing process after the problems they had with the earlier heads that year? I had just never heard that this was done that far back. I asked how they knew they had been hardened and the re-builder said because of the purple color of the metal in the area in question. He was fairly certain that the engine had not ever been worked on since new as well. Clay/Lexi

[J. Gomez]

Of note is that these heads are the "2nd generation" ones from that year. Perhaps GM added this to the manufacturing process after the problems they had with the earlier heads that year? I had just never heard that this was done that far back. I asked how they knew they had been hardened and the re-builder said because of the purple color of the metal in the area in question. He was fairly certain that the engine had not ever been worked on since new as well. Clay/Lexi

Clay,

The only clue I can offer you about the valves is; “if you notice a thin casting around the stems of valve guides then those are the original ones.”

Is that considered to be part of the “flame hardening” can’t say for sure.    I believe GM did flame hardening, from what I've found is the GM used the process in the early 70s for unleaded engines not sure if it was done earlier.   

I’ve notice on both my sets of 1956 and my other set of 1961 heads the valve guides stems were covered with a thin layer of casting which I had to remove a bit from the top to place the cup oil seal, instead of using the standard “O” ring around the valve.

Just a bit of FYI.

[Lexi]

Will quiz the re-builder some more on this when I see him next. Unfortunately I probably won't see the heads again until they are assembled and on the block. Clay/Lexi

[Lexi]

Update for you detail oriented members & '56'ers': Was at the machine shop yesterday and chatted with the mechanic who worked on those heads. I asked again why he said they were "flame hardened". He replied that the color of the surrounding metal gave it away; purplish shades as well as swish like marks of color change (not always purple) as well. He also said that when he put a stone to it (the seats I presume), it was immediately clear that he was working with hardened steel. He could tell by the feel of how the stone worked the material. He also was of the opinion that the engine had never been disassembled. Despite the poor lighting & shooting conditions I took a couple of photos for those interested in this information. Hope the pictures show some of the metal color changes discussed. Upper right quadrant at about "2 o'clock" from the spark plug hole, and also valve seat area, note the shades of purple hue. Is more apparent in person when you can rotate the piece in your hand and catch the light just right. Image had to be compressed for posting on this site so hope it still shows.

In the past I have heard comments that 1956 Cadillac heads were of "cheap" quality. The machine shop people were amazed at the level of finishing in these heads. "Cheap" probably isn't the best descriptor to use, though that year of head (especially the early ones) were certainly plagued with design flaws, (and 'hot' running engines probably did not help). In the shop they showed me an early '60s Ford set of heads. There was no comparison. The Ford head combustion area was unfinished cast iron though Cadillac had highly polished this area apparently to assist in the retardation of deposit build up. Just another example of Cadillac's attention to fine detail. This discussion with the machine shop came up as they recommended not to install hardened seats as those OEM appear to be already hardened.

Perhaps worthy of discussion for those in the midst of a 1956 Cadillac 365 ci engine rebuild. To install or not to install hardened valve seats, (following a detailed examination of your cylinder heads first). Also note the close proximity of the intake and exhaust valve ports as compared to that of the Ford. Possibly another design element that may have contributed to premature cracking. The shop was slightly apprehensive about machining this area to accept hardened seats though they showed me a set that would work. Cheers. Clay/Lexi

Clay/Lexi

[Dave Shepherd]

Looking closely those seats look like replaceable inserts, ask the machinist about that.  Very nice finish in the casting.

[Lexi]

Hmmm... I will, though that matter never came up. Will try and follow up on that. Those in the shop were in awe at Cadillac's attention to detail in these castings. At first I thought they were fondling a girlie magazine centerfold, but nope, it was these Cadillac heads! If they never were touched, then again I wonder if this was done to assist in combating the reported failures of the first generation heads that year. I just did not think that GM did that sort of thing then. Clay/Lexi

[Jon S]

I don't believe any 365/390 had factory hardened heads. There was no one envisioning the removal of lead from gasoline in the 1950's/1960's. And why spend the extra money for no purpose.

[Lexi]

That is what I thought, though the evidence here suggests otherwise. Hence this topic. Today I was at my steering pump rebuilder and examined the parts from a power steering pump for my 1956 Cadillac. The rebuilder commented on the quality of materials used, even asking where I got it from as it appeared unused, at least condition wise internally. I assured him that it was well used. He showed me a heavy cast piece, (perhaps a valve body), that had evidence of "case hardening" as he put it, and pointed out the "wave-like" marks still visible on the steel wall. They are usually gone after much use he added, but they persist on this particular unit. Perhaps Cadillac routinely hardened various valve components even cylinder head valve areas, though the demise of leaded gasoline was not forecast at that time? Actually, there was a reason to harden them at least for that year because of the high failure rate of the first generation heads. The set in question is a 2nd generation set. I am not sure what changes were made to combat the problems experienced by the earlier heads (cracking), though perhaps flame hardening of that area was something done with that in mind? The big question is whether the engine was ever worked on once it left the factory. The machine shop said no. Bolstering their opinion is that the engine had very low mileage, reportedly 27,000 miles and sported what appears to be a lot of original Cadillac engine dark blue paint. So it is a mystery hence my posts. Clay/Lexi

[Jon S]

I know I researched the topic of case hardened heads relative to my 1958 30 years ago and concluded they were not. That prompted me to buy numerous cases of tetraethlylead while it was still legal to do so.

[Lexi]

The evidence here suggests otherwise for this example, hence the reason the rebuilder strongly suggested NOT to have hardened valve seats installed as they would be pointless, (the ones there are already hardened). I explained to them that their findings and opinions are contrary to what I have been told about this year of head. They were amused but unmoved. Although we must follow where the evidence leads, I do not feel that the matter is conlcuded. I will look further into this and see if a definitive answer can be found. For the time being I am now totally confused on this issue! I put this forward for others more knowledgeable to ponder. Clay/Lexi

[Jon S]

I'm anxious to hear their findings.

[J. Gomez]

Clay,

Hmm now you did it “opening a can of worms..!” 

You bring a good topic if Cadillac sought at resolving the issue with the early heads cracking by installing harden valve seat to reinforce the weak area in the second generation of ’56 heads by not re-casting a new set, before they got revamped in ‘57.   

The picture below are from my original ’56 head build was March 26th day and these are bad (as always at either of the two center cylinder) you can see the blue mark made by the machine shop. 

Now I can’t tell if the seat have the bluish color (I do not think so) since they were not touch after finding the problem, so I would guess these maybe the standard ones.

So my friend since you were the trouble maker on this topic, “tag you it” in the research.   

[fishnjim]

Unless you've owned the car since new, or have complete day one documentation, and depending on the mileage it's more likely they were repaired at some point.   
Hardened seats use a different metallurgy, so he'd have to analyze the seat material to tell if factory.   Eyeballs aren't sufficient.
Simply heating the cast/original seat with a flame won't accomplish hardening.   You have to apply a gaseous atmosphere to coat the surface to obtain a "case" hardened coating.   It's more likely they heated the head to accept the seats via shrink fit.

[Jon S]

Very few on this Forum have had their cars since new. I come very close in that my dad bought mine New and the engine has never been disassembled. I use TEL for both valve lubrication and octaine increase. BTW, I have no intention of removing my heads for inspection.

[Dave Shepherd]

Again, as in my Chrysler Hemi, it had pressed in hardened exhaust seats only, you could see this looking closely and the parts book listed exhaust seats only.  Sure looks like that in one of the pictures above.  Btw, agree with fishnjim.

[Lexi]

Yes, Jim I agree with your comments on metal hardening. Though with respect to the seats, I asked the shop if these are original or have they been replaced at some point in the past, (as Dave Shepherd suggested). They were adamant that they were factory and said they were integral to the head. As for case hardening, it goes back a long way. It was used extensively in the 19th century and other metal hardening techniques go back centuries. I know that heating the metal while exposing it to various compounds for the purpose of hardening the outer skin as well as some penetration, yet leaving an inner core 'soft' (to counter the brittle aspect of hardened steel), seems reasonable for this process. The degree of heat, penetration of carbon (as I recall), and time, if correct, yields a hard wear resistant contact surface without being too brittle, (hence the soft core).

Had the seats been replaced I know that sometimes an arc welder is used to change dimensions to assist removal, but the shop again was adamant that was not the case here and that the discoloration of the metal in the heads would not have been caused by that anyhow. As there is evidence of case hardening on my steering pump component, is it reasonable for GM to have used a similar well established technique to address cylinder head issues that crept up during the 1956 model year? Seems reasonable to me. The rainbow-purplish-brown hues observed in both head combustion areas are not restricted to the valve seats, but also to the surrounding chamber as well.

Perhaps most revealing is what I have NOT been able to find on this matter. A check of the index for the 1956 Cadillac Serviceman publication did not reveal any mention of Cadillac changing cylinder heads that year, though other 'ugly' matters are addressed such as hydramatic and over heating issues. Why the apparent silence on what seems to be a rash of head problems that year? I will check my 2 binders of bulletins and see if there is any mention of this. I know in the past other members have asked why the change of cylinder heads that year, but all I recall was reasoned speculation. Don't recall seeing any period GM bulletins or notices that detailed why the change took place and what was done to correct the problem. This apparent reticence is of interest in itself. My search for answers continues as I still find the matter puzzling. Clay/Lexi

[Lexi]

The February 1956 Cadillac Serviceman issue made note of "modified cylinder heads" (page 9), as being potentially installed on cars after engine number 033849. The reference was made in an article on "Detonation Relief". This was expanded on in an early issue of the Round Table publication. Will look further into that tomorrow and see if there are any references to what was modified on the cylinder heads. Clay/Lexi

[Jon S]

"Detonation relief" sounds like lowering the compression or redesigning the head as opposed to hardening the head. JMHO