637 V8 gas engine

[65GMCKV4000]

This followed me home. :upyes:

[LEWISMATKIN]

IS THIS CRACKERBOX A '67 OR A'68????:coolphotos::coolphotos::coolphotos:

[65GMCKV4000]

1966

[65GMCKV4000]

Try this again. 1966 GMC Crackerbox FE model with 637 V8

[65GMCKV4000]

Front view.

[WE7X]

WOW! What a find.
Looks to be pretty decent.
How far away did it come from?
Rod Johnson
Issaquah, WA

[2-Ton]

A lot of folks have heard about the 702 twin 6, but very few know about the 637 Magnum V8.
The 637 replace the 702 twin 6 in 1966.

I have one in a 67 GMC COE fire ladder truck.
About 15,000 miles on it and it runs great.
Sucks gas like there is no tomorrow.

Parts are hard to find.
Fuel pump quit on me a few years ago and cannot be found anywhere.
Mounts on the front top of the motor and has about a 14 inch reach arm on it.
Ended up mounting an electric fuel pump at the tank.

The pictures and story here.
https://www.stovebolt.com/gallery/king%20don%201967.html

Don

[Funky61]

Great Story on the Fire Truck purchase! Would you mind posting a close up photo of the V8 emblem I see on the front, Thanks.

[65GMCKV4000]

Rod, a friend of mine told me about it. It had been on Craigslist awhile back and it never sold. It came up again and I jumped on it. Came out of Colville WA and before that Idaho. Here is a picture of the emblem.:upyes:

[65GMCKV4000]

I also picked up a 637 this spring out of California. I got it freed up, but haven't got it running yet. I also got two emblems with the engine from California. Good to have the extra parts.

[Funky61]

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.

[65GMCKV4000]

Great story on the fire truck Don!!!!

[65GMCKV4000]

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.

[LEWISMATKIN]

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.

[bigblockv6]

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:

[bigblockv6]

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.

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.

[LEWISMATKIN]

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????

[bigblockv6]

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:

[LEWISMATKIN]

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.

[WE7X]

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

[LEWISMATKIN]

and while dad's shop was open and in it's original location, I ran across a guy who had a 637 overhauled. He took his shaft to Graves Plating in Florence, Ala., and had it chrome plated. It was running fine at the time, but that was about '80-'81.

[bigblockv6]

Louis, a few months back I bought a set of those valves, though the seats are the same diameter the stems are shorter than the GMC valves. Evidently it would require the valve springs. This won't work with my setup since I'm running a custom ground high list cam with longer Ford 390 valve springs. The correct way for me to go is with some custom Manley stainless steel exhaust valves:ahhhh:

[LEWISMATKIN]

how much shorter, Pete??

[2-Ton]

Yep that the engine, But the picture does not show how really big it is.
The emblem is the same as Mine has on both sides of the cab.
No pictures of the engine, but once you get past the pirate ship and skin you will see a few other GMC's that could be for sale.
https://www.flickr.com/photos/149052261@N05/

Don

[bigblockv6]

Most likely the original exhaust manifolds cracked and replacements were impossible to find so someone fabricated their own.

[bigblockv6]

how much shorter, Pete??

I'll get the measurements out tomorrow when I get back home and I'll post some picks of both the Cat and GMC valves for comparison.:thumbsup:

[LEWISMATKIN]

thanks, Pete!:biggringmc::biggringmc::biggringmc::biggring mc:

[BobBray]

Neat and very rare truck! The only gasoline powered 'Crackerboxes' were the '66-'68 FE/DE versions with the 637. To my knowledge the 702 V-12 was never a regular option in the 'Crackerbox', though it was in the L series 'Steel Tilt'. There were Toro-Flow 637 powered 'Crackerboxes' as well, I would imagine those are just as rare.

[LEWISMATKIN]

bob, some of the DW & DL did have the 702 in them. At least that is what my parts books from that era state. It was also in some of the DB cabs.

[bigblockv6]

I'll get the measurements out tomorrow when I get back home and I'll post some picks of both the Cat and GMC valves for comparison.:thumbsup:

The valves are 1/2 inch shorter over the stock GMC valves as you can see in the pics. It's possible there may be longer versions, if not I'll just go with some Custom Manley stainless steel valves:upyes:

[BobBray]

bob, some of the DW & DL did have the 702 in them. At least that is what my parts books from that era state. It was also in some of the DB cabs.

Yes, those were the Steel Tilts, not the Crackerbox aluminum tilt cabs.

[BillT]

Interesting truck. Never heard of a 637 in a Cracker Box before. I just flashed through the replies real quick and didn't noticed, but what kind of Trans does it have?

[BillT]

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.

The Crankshaft can't be that weak, lol.

The '71 9500 I used to drive had a 637 V-8 Gas with a 10-Speed Road Ranger behind it. I was the 2nd driver of the truck. The first driver was old school 5-Speed, 2-Speed and never learned to shift the RR properly. He did fine Up-Shifting, but never learned and probably never even wanted to learn how to Downshift a Non-Synchro Trans. I rode with him a few times and could not believe how he would lug the heck out of it, which we all know wreaks havoc on a Crankshaft. I would always joke saying that the Crankshaft is going to end up on the front seat someday.

Anyway, I left the company after about 3 years. Then one day saw the truck when it was about 15 years old, for sale as is by another owner. And guess where the Crankshaft was?

We would haul some heavy loads with it. Probably up to 48 or 50,000 on a 46,000 GVW truck. It's amazing how long that Crank actually lasted.

[65GMCKV4000]

It has a 10 speed transmission.

[BillT]

It has a 10 speed transmission.

Just curious, is it actually a 10-Speed Fuller Road Ranger?

[65GMCKV4000]

Yes I think it is.

[BillT]

Looks like it is. Now what is interesting, if the Engine and Trans are both original to the truck, this means that you have only the 2nd Engine-Trans combo that I have ever seen, as well as ever heard of, since I first saw our truck that got delivered in April of '72.

All the 637's out there that I know of are either 5-Speeds, 5-Speed/2-Speed Rear or have 2 Sticks.

Would love to go for a ride in your truck sometime, but we are about 2500 Miles apart, lol.

[65GMCKV4000]

BillT
You are welcome anytime to come out here and go for a drive in the crackerbox. I also have a 62 GMC 7000 with the 702V12 you could take for a spin too!!

[POWERSTROKE]

I was never around any Crackerbox GMC's but the guy Dad drove for the longest hauling livestock had two L-series Steel cab GMC tilt cabs, one had a Working '5th, from high 3rd you went to low 4th, low 5th, shifted the axle to hi, and 4th, then 5th in high. The other one had a conventional 5+2. Both either had 401 or 478 engines. Later on he bought a Chevy C70 with a Toroflow diesel that had the cab of a GMC B series. Bet that's a pretty rare truck today! It was actually Dad's favorite truck once he disconnected the exhaust stacks from the top rear corner cab mounts, they set up a deafening vibration in the cab, but the truck had fair performance with the BIG V-8 Toro-Flow, 5+2, power steering. At that time his other two trucks were Emeryville's, climbing up and down into and out of them got old, Dad let the younger drivers run them.

But anyhow, Awesome fire truck. Bet you could make good money washing 2nd, 3rd, and 4th floor windows, cleaning gutters, pruning trees, etc. I'm not a fan of ladders!

The Crackerbox was the epitome of a minimalist truck. Minimum cab, short wheelbase, big engine and transmission. I drove a couple TransStar's, a CL9000 Ford, never got into the Astro 95 or White Road Commanders my company had, all their tiltcabs had bunks. Put lots and lots of miles on a pair of RoadBoss 2's and an S2200 Binder.

[BillT]

BillT
You are welcome anytime to come out here and go for a drive in the crackerbox. I also have a 62 GMC 7000 with the 702V12 you could take for a spin too!!

Appreciate the invite. Wish we were closer, lol. Nice collection of trucks there. Tell me more about the GMC in the middle. Looks like it has a Heavy Front Axle with the Wide Fenders on it.

[BillT]

one had a Working '5th, from high 3rd you went to low 4th, low 5th, shifted the axle to hi, and 4th, then 5th in high.

That sounds like a Clark 5-Speed Trans. I had one in the '62 6500 and in my '67 7500. It liked it as I could go through 9 Gears and only have to downshift the Rear twice.

[65GMCKV4000]

It is a 62 4000 with a 305 V6, wide fenders and very large front end. Was a brush rig for the local fire department here where I live. Has 15K original miles. 1000 gal water tank with Wisconsin engine driven water pump. The truck was originally a 2 wheel drive, converted at the dealer to 4x4.
I also have a 65 KV4000 with wide fenders and the same front end and transfer case.

[LEWISMATKIN]

The Crankshaft can't be that weak, lol.

The '71 9500 I used to drive had a 637 V-8 Gas with a 10-Speed Road Ranger behind it. I was the 2nd driver of the truck. The first driver was old school 5-Speed, 2-Speed and never learned to shift the RR properly. He did fine Up-Shifting, but never learned and probably never even wanted to learn how to Downshift a Non-Synchro Trans. I rode with him a few times and could not believe how he would lug the heck out of it, which we all know wreaks havoc on a Crankshaft. I would always joke saying that the Crankshaft is going to end up on the front seat someday.

Anyway, I left the company after about 3 years. Then one day saw the truck when it was about 15 years old, for sale as is by another owner. And guess where the Crankshaft was?

We would haul some heavy loads with it. Probably up to 48 or 50,000 on a 46,000 GVW truck. It's amazing how long that Crank actually lasted.

Very true, very true. However, I was speaking from a repair standpoint, not a longevity standpoint. Dad's shop replaced a number of crankshafts in the Toro-flows while a GMC dealer for Georgia Highway express. They would not had to have been replaced if they had been Tocco-hardened. I have seen only 1 637, and it was in a steel tilt cab. The other 637 I only know from speaking to the owner at the time. When I look at the repairability of an engine, I look for things such as the design flaws, like the type of hardening on these shafts. I can't for my life understand why these crankshafts (gas & T-F 637 and T-F 478's) weren't tocco hardened.:banghead::banghead:

[LEWISMATKIN]

Yes, those were the Steel Tilts, not the Crackerbox aluminum tilt cabs.

Bob, the D-cab was the aluminum cab (crackerbox).:thumbsup:

[LEWISMATKIN]

Yes I think it is.

Road rangers of that era would more than likely been the RT-610 or RT-613 series transmission. These trannys are rated at 600 ft lbs of torque and were found behind many gas-engine trucks of all major brands of the day. This one looks like the RT600 series of Fuller transmission.:coolphotos::coolphotos::coolphotos:

[2-Ton]

Anybody know where to get a fuel pump for one?
Mine went out a few years ago and I ended up covering the hole with a plate and mounted an electric one on the frame.

Napa books all said discontinued.

[POWERSTROKE]

That sounds like a Clark 5-Speed Trans. I had one in the '62 6500 and in my '67 7500. It liked it as I could go through 9 Gears and only have to downshift the Rear twice.

Yes! I'm sure you are correct about them being a Clark. Dad took the Whole Darn Family sometimes, Mom rode Shotgun, my Sister and I traded between the sleeper bunk and sitting on the doghouse. The truck tended to jump out of 5th, and got "Tarp Strapped" into 5th so rolling hilly roads were driven like a roller coaster, just shifting the 2-speed.

Too bad GMC didn't Tocco harden the 478 & 637 crankshafts. International Harvester Tocco hardened crankshafts in the old Farmall H & M model farm tractors. Some just months away from 80 ( eighty ) years old are still running regularly with the original crankshaft. I've only ever seen ONE broken M crankshaft and heard of one other. Undersize main & rod bearings are NOT common in them.
Company I used to work for Nitrided lots of parts. Biggest advantage of Nitriding was the low temperature the process exposed the parts to, nitrided parts needed little if any finishing after nitriding. Depth of hardness was not real deep but deep enough. If crankshaft was reground nitriding would have to be redone.
Chrome plating crankshafts was common, but not used much anymore. On a stressed part like a crankshaft pealing the chrome off was a possibility. A plasma metal spray technique would be better, but enough heat is put into the crankshaft all the journals would have to be reground.

[BillT]

Road rangers of that era would more than likely been the RT-610 or RT-613 series transmission. These trannys are rated at 600 ft lbs of torque and were found behind many gas-engine trucks of all major brands of the day.

Right, I believe the RR in my '71 9500 (J-Model, Conventional Cab btw) was an RT-610.

[bigblockv6]

Too bad GMC didn't Tocco harden the 478 & 637 crankshafts. International Harvester Tocco hardened crankshafts in the old Farmall H & M model farm tractors. Some just months away from 80 ( eighty ) years old are still running regularly with the original crankshaft. I've only ever seen ONE broken M crankshaft and heard of one other. Undersize main & rod bearings are NOT common in them.


I know GMC Tocco hardened 401 and 478 crankshafts back in the 60's, I have a factory shop manual that mentions it. In the 70's Tocco process was replaced with Tuftriding according to my factory parts manuals, they recommended after turning the cranks to have them Tuftrided, the posibility Diesel versions didn't have this process. When I had the crank turned on my 478 I told the machinist to have it tuftrided he told me that process was replace with Nitriding so that's what was done on my 478 crank:upyes:

[2-Ton]

Really!
No answer to a good question, on where to find a part for a 637?
The 637 replaced the Twin Six.
And no one has any advice on how to find a new fuel pump?
Do you even know where it is mounted on the 637?

[Funky61]

2-Ton;

I've gotten some parts from EBay a few times and even went to NAPA and asked the Guy to look in his Old catalog stash as opposed to the computer. I've had several "New" pumps fail because I guess they were too old stock and the diaphragms would break.

Is the old one rebuild-able?

So in the end, I went with a Carter electric and no more problems.

https://www.summitracing.com/oh/parts/crt-p4070/overview/

*PUMP LOCATION-I think some one mentioned the fuel pump is located on the top front of the engine mounted up with the arm pointing down looks like.

[2-Ton]

Thanks Funk
I did the same thing.
NAPA pulled the old hard copy out and showed me where it was discontinued years ago. Thought about taking the arm off and putting it on another pump.
But went with an electric pump.
The old pump is not rebuildable.

And yes, it is mounted on the front, top center of the engine with the 12 inch arm vertical.

Story of the truck here.
https://www.stovebolt.com/gallery/king%20don%201967.html

Don

[Michael S. Wilson]

I'm the one who has the running 637 on youtube. The pump you see on the engine is actually for a v6. I simply changed the arm like Two Ton suggested. I do have a couple of those pumps now if someone needs one. Not sure how long they sat on the shelf though.

[BillT]

I believe I put your video on the boards over at Heavy Haulers on the '67-'72 Chevy truck site. We have some 637 fans over there as well.

I'm also the one that used to drive a 637 V-8 Gas in a GMC J-9500. It was a '71 model with the very rare combo of a 10-Speed Road Ranger behind it.

[Michael S. Wilson]

I've never driven anything with a 637. I need to get this one I have into something. I'm going to try and get a HEI from a Buick 340 on it. I got some extra adapters from We7x.

[bigblockv6]

You would need an HEI from a Buick 350, the 340 was long discontinued by the time the HEI was introduced.

[Michael S. Wilson]

You're probably right. I got one on Ebay that fits them all the way back to the 215. It was probably for a 350.