Re: 637 V8 gas engine
 

Wow Nice pic; I had never seen the factory exhaust on those engines. Do they have a four barrel carb and what does the air cleaner look like?
No rush just curious about the 637.

Re: 637 V8 gas engine
 

Great story on the fire truck Don!!!!

Re: 637 V8 gas engine
 

Hey Funky61 The picture of the engine on the flat bed has home made headers. They came with a cast iron exhaust manifold. I will try to get some pictures for you.

Re: 637 V8 gas engine
 

Only one weak point I know of on these engines is the crankshaft. The crankshaft on the 637 is not flame-hardened(called Tocco hardening or armasteel), instead, it is TUFF-RIDED, a chemical washed on hardener only penetrating .006" into the surface of the shaft. In order to provide undersize bearings, the shaft must be rehardened by either re-TUFFRIDEing the shaft, or chrome plating the journals. On this engine, please use a high-quality SAE30 or SAE40 engine oil (preferably diesel approved). The 305-351-379-401-432-478 gas engines can be resurfaced w/o going to the expense of this process.

Re: 637 V8 gas engine
 

I remember going through some manuals and GMC actually recommended a hardening process called "Tuftriding" after turning the crankshafts . When the crankshaft for my 478M was turned down I requested that it be rehardened, was no problem with my machinist he sent it out for that but told me there was a newer process that superseded Tuftriding which is "Nitriding" and that's what was done on my 478's crankshaft:upyes:

Re: 637 V8 gas engine
 

These engines only came with a 2bbl, the same Bendix/Stromberg WWC carb used on all 401, 432, 478 as well as he 351E and all other Magnum engines. You would think a 4bbl would be more appropriate for an engine of 637 cubic inches. I think a Holley 500 carb would be the first upgrade to do.

Re: 637 V8 gas engine
 

glad to know that there is a more modern method of rehardening these "TUFFRIDED" shafts, Pete. How satisfied were you with the nitride rehardening of your 478M-L/D????

Re: 637 V8 gas engine
 

Lewis, ten years ago I took a class in metallurgy and it mentioned a hardening process called Nitriding, so I can say I'm very happy the crankshaft on my 478 go this treatment topped off with Clevite bearings. I'm real hard on my stuff so the bottom end will hold up fine, my biggest worry now is those hollow stemmed sodium filled exhaust valves, I should have addressed the issue when the heads were built, specially when I was told these engines are notorious for sucking up valves from over revving, that's why GMC put governors on them. So a move in the future will be to replace those exhaust valves with something better:upyes:

Re: 637 V8 gas engine
 

pete, somebody in the old forum/club replaced his valves with ones from a cat diesel engine. I don't remember who it was, but at the time I thought it was a great substitute.

Re: 637 V8 gas engine
 

That is a unique exhaust manifold. I wonder if it came from some sort of a stationary engine application.
Rod J
Issaquah, WA