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We're doing a head machine job on the 427 to plane the surface and stop exhaust manifold leaks. During this job, we're thinking about installing hardened seats and stainless valves, as recommended by our mechanic (his quote on seats and valves about $400-450). I've heard various opinions on the need for this in an old engine. I would probably install them if we were racing it or dragging it or running the engine hard, but we don't drive it like that. What do you lot think? I searched the forum about hardened seats and found some good info, but no real discussion as to the need for it. Thanks in advance.
 

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That's what I get, too. Lots of people repeating what they heard and some theories but not much else.
 

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If you are having the heads done, it's good insurance to put the seats in, but if you have a running engine, the only real difference with non-hardened seats will be reduced valve job life. You might go 60,000 miles instead of 100,000 miles, for example.
 

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While you have the heads off check the seats and see if they are recessed check the guides and how the valves faces look. Then just do the work that is needed. If you are not racing it and just cruising it don't spend the money if it's not needed.
 

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20 or so years ago I rebuilt the 390 in my 1969 Camper special. I bored it and had to replace a sleeve and valve job. I broke it in and drove it every day for 2000 miles. I took it on its first vacation carrying a 12 foot slide in camper. 800 miles into the trip I ran out of lead additive. I was pulling a hill in western Pennsylvania and it lost power and starting running rough. I limped it to my fathers house and I had almost no compression. I ended up shimming the rocker stands to get home 500 miles. Sunk all the valves into the heads. I always install hardened seats since then. I scored a cylinder and it burn oil after that. I learned my lesson.
 

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This is just highlighting the main points. If you want a bit more, along with a bit of sarcasm ;) try here and here. Ignition timing and rich running is what erodes valve seats, and why distributors without vacuum advance are "race only". Without a properly functioning vacuum advance, the engine is running effectively retarded and the exhaust valves literally get red hot. Sometimes you can even hear it ping at cruise from end-gas detonation at the hot valve. There's something to think about - adding timing to stop detonation. Whoda thunk?

The other common cause as stated is rich running, where the carbon prevents the valves from sealing fully, causing rapid gas-cutting erosion. Look at it this way - if unleaded fuel was the cause of valve seat erosion, then A) all classic car engines would crap-out rapidly, and B) hardened seats for unleaded fuel would be installed from the factory. Well, neither is true. We've had unleaded fuel by law since the mid-'70s and until aluminum heads, they made them the same way as the 1960s and before using plain cast heads with induction-hardened seat areas, without special seats.

There are other lesser causes that can combine to erode valve seats, but they are not from unleaded fuels. Testing has shown valves and engines are actually more prone to damage with lead, but that's a whole other subject. My 2¢ of suggestion is to do a normal rebuild on them if necessary, doing whatever they need to do the job properly. If they need new seats anyway due to valve sink or if grinding will cut past the old factory hardening, then fine. If not, don't spend the extra money doing them, and instead spend it tuning your spark and fuel to your specific engine at all RPMs and all loads. Your wallet will appreciate the increased MPG too.

David
 

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Unless the seat inserts you're having put in are Stellite ($$$) then there's no difference from what you have now. Plus you're cutting material out of the head and potentially weakening it. Standard insert seats should be used for repair only.

Most factory valve seats are induction hardened and should be fine unless they've been ground heavily.
 

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Unless the seat inserts you're having put in are Stellite ($$$) then there's no difference from what you have now. Plus you're cutting material out of the head and potentially weakening it. Standard insert seats should be used for repair only.

Most factory valve seats are induction hardened and should be fine unless they've been ground heavily.
Yes, Stellite seats are hardened. Most other seats are the same material you're carving out of the head.

Unless an engine is expected to see severe service (towing for extended periods of time under high load) it probably does not need hardened seats. A hotrod 'toy' pretty much never needs hardened seats. They don't encounter continuous hard loads for expented periods of time, and don't see that many miles.

I never installed hardened seats in my 289 heads, and those were used for 10-12 years running 10 second 1/4 mile times on the bottle... as well as thousands of street miles... and they held up great. Zero signs of recession.

I have seen a really nice set of ported heads ruined by a machine shop that tried to install seats... who hit water while cutting them out. It's generally a 'money making' up-sell by the machine shop in most cases.

Unleaded fuel came out in 1975. Engines made in 1975 or later should have induction hardened seats from the factory.

Good Luck!
 
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