425 NH Hardened Valve Seats

[55Super56R]

I bought a wrecked '66 Riviera, running 425 Nailhead and TH400 switch pitch, as a parts car for a 55 Super 2 dr hdtp. I am in the process of rebuilding the 425 and have had differing advice about installing hardened seats in the heads. A reputable local machine shop insists that I have to install the seats but my local Buick gearhead says that these old head castings have alot of nickel in them and the seats aren't needed. I also understand that the waterjackets are very close to the valve seats and it is quite easy to ruin a head when installing the seats.

The motor will be built almost stock - mild cam with stock springs, etc. as a cruiser motor for the 55 Super.

Any advice will be welcome.

[wkillgs]

The advice from the Nailhead guys on the internet say do NOT install hardened seats.
Friend of mine had a shop do his heads with the hardened seats.
I had my heads done there too, Shop told me I would ruin the heads if I didn't put seats in, but I'm stobborn, and said NO, I'll take my chances.

My buddy went to start his engine up for the first time, and found one cylinder full of water. Word is it was a leak from the valve seat insert.

So far, it looks like I made the better choice. We'll see how it holds up after a few thousand miles.

I bought a wrecked '66 Riviera, running 425 Nailhead and TH400 switch pitch, as a parts car for a 55 Super 2 dr hdtp. I am in the process of rebuilding the 425 and have had differing advice about installing hardened seats in the heads. A reputable local machine shop insists that I have to install the seats but my local Buick gearhead says that these old head castings have alot of nickel in them and the seats aren't needed. I also understand that the waterjackets are very close to the valve seats and it is quite easy to ruin a head when installing the seats.

The motor will be built almost stock - mild cam with stock springs, etc. as a cruiser motor for the 55 Super.

Any advice will be welcome.

[55Spcl]

wkillgs,
You were right in not letting the shop install hardened valve seats. Not only aren't they needed, but as your friend found out, the material between the valve seats and the water jacket is pretty thin by design. It's not uncommon for a machine shop to bore through into the water jacket and wind up with a boat anchor while attempting to install hardened seats.......

I rebuilt my 401 (2x500cfm AFB's, St-10 4-speed and a pretty hefty cam) about 8-years ago, without hardened seats, and put approx. 5k miles a year on it. I've travelled several times to Bowling Green, Ky. (about 800 miles each way) totally on Interstate highways , at 65-75 mph and running at 2800-3000 RPM; run around town locally; and have even gone down the 1/4 mile on occassion, and there's no sign of any problems vacuum, leak-down and compression tests all show the engine to be in great shape.

I also have a car with a Chevy 327 and one with a Chevy 235. Both those cars have been run for many years without hardened seats or any type of additives and there's no signs of any valve recession in either of them.

In general, I believe the whole valve recession question is, in most circumstances, much ado about nothing! We ran "white gas" (unleaded) gas in engines for many years, back in the 50's & 60's and never had any problems.
-Bob

My 2¢

[55Super56R]

Thanks to all for the advice on my 425 heads.

A couple more questions:

Is it necessary, or a good idea, to have the tops of the valve guides machined so I can use better valve seals on the intakes and exhausts - my '66 NH has seals on the intakes only now.

I've rebuilt Chevy's and Pontiacs for years and gotten used to having the ability to adjust each rocker to set the pre-load on the lifters. My NH rocker assemblies are nice and tight and no real signs of wear on the rocker tips - am I OK to reuse the stock push rods with new lifters or do I need to buy adjustable pushrods? How sensitive is the NH engine to minor wear in the valve train that results in slight variations in lifter pre-load?

Thanks