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Old 10-29-2002, 05:41 PM
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Post Hardened valve seats??

I have the chance to get a 71 nova engine cheap with a power-glide. According to the book the only 6 cylinder engine in that year is a 250 cid. It would basacally be to replace a 67 194 engine. I know the 67 engine doesnt have hardened valve seats would this 71 engine have them??

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Old 10-29-2002, 08:25 PM
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NOPE! Not unless they were changed once.Very few had hardened seats until 74 unleaded gas.
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Old 10-30-2002, 02:26 AM
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Actually they might. It was around that time that they started to convert over. I don't know enough to say for sure if the little six did, but I think some others were hardened that early.
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Old 10-30-2002, 01:24 PM
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don't know that it really matters on a street engien. I just tore down my 235 Chevy 6 for a complete rebuild after the 70,000 miles I put on it with the cheapest unleaded gas I could find and ???? miles B4 I got it 'cause the spedo was broken. The whole valve system looked great and the seats looked like I could have just rerun the valves without even lapping them. Perfect. Rings were another story! They had long outlived their useful life. I am installing hardened seats since it is cheap to do when rebuilding an engine but I would have no problem running an old engine on the street on unleaded.
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Old 10-30-2002, 04:54 PM
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71 did not have hard seats, if you plan on working the motor you will need to have seats installed, GM started to harden seats about 73 and the early versions were not good quality.
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Old 10-31-2002, 07:29 PM
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I still don`t have hardened seats in my 68` 041 castings, all I do is run lead additive. heads have been reworked 4 times, seats still look good.
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Old 10-31-2002, 07:38 PM
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I am in the middle of a 72 Pontiac. It shows 108,000 miles. The seats are original and look good. Worn, but eminently grindable. The car was owned by a farmer and had the @!$#% run out of it by his kids as it passed through the feeding chain. Don't think you need to worry.
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Old 11-01-2002, 07:21 PM
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I think it's kind of funny how machine shop guys like to push hard seats. They are not necessary unless you just plan on running the sucker all of the time, and alot of miles, maybe over 50,000 miles. It takes a long time for seat recession to take place from using unleaded fuel. Most hobby engines will never need hard seats.
Alot of machinists like to install them because 1:they create alot of revenue and 2: The seat cutters on modern seat and guide centers work best on a hard seat as opposed to a stock iron seat{less chance of chatter with the carbide cutter on a hard insert}, and it's convenient.
Also, an insert on a performance cylinder head can diminish flow to some extent, alot of the good shape of the factory seat area is gone once the head has been chopped for seats.
There are good reasons to use inserts, one of them being sunken valves from multiple valve jobs, or repairing small cracks ect, but I just never could see putting hard seats in unless just absolutely necessary.
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Old 11-02-2002, 04:26 AM
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I agree with the rest of the posts. I have four cars, all over 100,000 miles with no hardened valve seats, and they all run fine.
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Old 11-02-2002, 05:33 AM
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Ditto!
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Old 11-02-2002, 08:39 AM
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then why are virtually all heads since 1974 hardened? and why do i get at least one pair a week of early heads with the center exhaust seats receded or gone? exhvalve seats are a must with modern fuels!!!!! Why ain't i rich from putting in all these "unneeded" hard seats ?

[ November 02, 2002: Message edited by: BOBCRMAN@aol.com ]</p>
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Old 11-02-2002, 09:23 AM
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Bob; We aren't saying seat regression doesn't happen. It obviously is a problem as your experience shows but it isn't as pervasive as some people let on. I contend that if you have a pre-unleaded engine that is running fine, and has been for 30 years, don't buy more trouble than you need. It is likely that the engine will die of some other cause than seat regression. If you are hot rodding or towing with an engine like that, sure the seats are going to go away but so is the rest of the tired engine! However if it is your daily driver and it hasn't failed by now, keep driving. Why spend the money on a valve job/seat replacement when there is no sign problems? Also, if that is the only repair you do on an old engine, the fresh top end will likely put too much stress on the tired bottom end and VOILA! spun rod bearings!

As I stated in my previous post, by all means, replace the seats in an early engine being completely rebuilt. As you state, it isn't that expensive if the heads are already off for other reasons.

I think we are say the same thing only different!

Incidentally, do you see a trend in the type or model of engines seem to have valve seat failure. Is it a certain brand or size of engine? Does it have more to do with the amount of load beign put on it, i.e., hot rodding, towing? Have you ever repaired seats a straight 6 engine? Or is it just random? Sounds to me from your description of the center two valves on a V8 being bad that the higher temperature there (heat x-over passage, surrounded by other cylinders, etc.) may be an indicator. That may be why my VERY old and tired 235 straight 6 didn't show any signs of seat regression after ?00,000 miles in the cheapest gas I could find!
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Old 11-02-2002, 10:15 AM
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willys, the seat problem is random, 4-6-8 doesn't matter, though ford 300 sixes seem to be the worst for seats and cracks(thatwill bring down all the ford people on me, Hey i own some Fords!) all of the different makes have production runs with some problems, this is buick and chevy countryhere so we see lots of these. i have done 216-235 with bad seats, but these engines are pretty reliable upstairs. the biggest problems with the small block no seat heads is excessive spring pressure and a little guide wear and you have a time bomb.
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