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Old 12-16-2011, 11:30 PM
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Hardened valve seats in older Pontiac heads?

Hi all

Went and had a conversation with the machinist at the machine shop that is going to do the work on my Pontiac 400...he's very experienced with Pontiacs and has a good reputation, I feel comfortable letting him do the work on my engine...

He brought up something that spooked me a bit...he said that occasionally the older Pontiac heads like my '68 72cc's can be a risky proposition when trying to install hardened valve seats, because of the large valve size in them and the lack of substantial machineable material between the valve seats...cracks are a real possibility...

He said if it goes bad, the head is ruined....

Is it worth the risk? A new set of heads will really shoot my already growing build budget all to hell...Should I just have him do a 3 angle valve job on the existing seats and run lead substitute additives in the fuel? This isn't going to be a daily driver or anything...just a fair weather weekend cruiser...maybe a bit of bracket racing from time to time...probably less than 3000 miles a year...

Thanks...

Mike

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Old 12-17-2011, 12:29 AM
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Hard seats are installed into Pontiac heads all the time. Yours will not have hard seats originally, IIRC hardened seats began around '74.

But if you're only putting limited miles on this engine like you say, you can get by w/o hard seats for now and install them in the future if you wanted. A "Pontiac style" 3-angle valve job is fine, just stick w/the factory 30 intake seat angle. There were heads close to your '68 heads- like #45, #46 and #47- that could have either 30 or 45 intake seats. You don't want to go to a 45 seat unless that's what they were originally. It's always a good idea to actually measure the chambers of both heads to be sure of the size.
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Old 12-17-2011, 09:44 AM
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Thanks cobalt...

He says that he's pretty sure the seat angle in those heads are 30 deg., but he always measures them to be sure.

I'm leaning more towards not risking the heads by having him attempt to install hardened valve seats...finding replacements in my area would be real tough, and those particular heads are on the spendy side when you do find them. My build is aready planned around that head size, I'd hate to have to switch direction midstream....

are the lead substitute fuel addititives available today worth a crap? Which one would I want to use?
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Old 12-17-2011, 02:54 PM
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Quote:
Originally Posted by MJS69

This isn't going to be a daily driver or anything...just a fair weather weekend cruiser...maybe a bit of bracket racing from time to time...probably less than 3000 miles a year...

Thanks...

Mike
If you're doing low mileage....more important without hard seats is long drives at the edge of the speed limit on the freeways, where your exh temp is high. LOTS of miles in short increments is safer than a few LONG hi speed trips. 1/4 mile trips down the strip excluded. So, keep that in mind. I've had many of my old car's heads void of hard seats with no problems.
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Old 12-17-2011, 03:40 PM
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Your machinist is correct about the possibility of ruining the heads.. Some early pontiacs are VERY thin on the center exhaust seats.. Only way to do them is to use an undersized, shallow, seat then cut out to size.. Even on a good install, there runs the risk of the seat coming loose under high heat/overheat type conditions..
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Old 12-17-2011, 07:29 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com
Your machinist is correct about the possibility of ruining the heads.. Some early pontiacs are VERY thin on the center exhaust seats.. Only way to do them is to use an undersized, shallow, seat then cut out to size.. Even on a good install, there runs the risk of the seat coming loose under high heat/overheat type conditions..

He mentioned that as well....I think overall the risk outweighs the gain...I'm going to skip the valve seats and just use a lead substitute....
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Old 12-20-2011, 11:53 AM
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We install seats in Pontiac heads all the time. We do it ONLY when "recession" has already occurred, or by specific request. An exhaust seat (the 45) of .090-.100" will disappate heat just fine, and unless you're towing, hauling loads or a lot of "lugging", the heads should be fine.

We use SBI "J-Loy" seats exclusively. They've done their research, and we've never "broken through" when using their specs. We also use a seat slightly smaller on the ID, to allow a more modern "profile" on the seat. There's virtually no "room" in the stock port for a "venturi" seat, so if replacing the seat, the opportunity presents itself. SB1812-1 is the recommended replacement. It's 1/4" deep. We use SB1812-14, also 1/4" deep, but 1 7/16" ID vs. 1 9/16".

If the "press" or interference is correct and the metal "folded" around the seat insert, it cannot come out. If the shop is "gun shy" installing seats, perhaps better left to someone not so "worried". This is not a "Pontiac specific" thing, it's a "machinist thing".

Jim
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Old 12-26-2011, 02:21 PM
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My machinist said the Pontiac heads don't need hardened seats.

I am building a 68 406 for my 74 formula and the first build I did was with 76 6x4 heads that gave me 8.3:1compresson. The flat tappet cam went south on one lobe so now i have it apart again and I'm using 67 670 heads with 72cc chambers. I took them in to have hardened seats put in and said that Pontiac used very good medal and I wouldn't have any problem running unleaded fuel with them. He said go home and smile I'll get your money next time. On my engine I need 80ccs to be at 9.5:1 so I unschrowded the valves and polished the chambers to get to80ccs. Now I'm assembling the heads. So I better get back at it.
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