The Stovebolt Site Forums The Shop Area Engine Shop Model 94 on a 248

I just bought a 1953 GMC 350-24 from a family friend that has been sitting for MANY years. I’m looking at what it’s gonna take to get it running, and have found that it has what I believe to be a 248ci engine in it, and I’m guessing the factory manual transmission.. From what I have read, these came from the factory with a Zenith Carburetor on them? This one appears to have a Holley 94 mounted on it… is it worth rebuilding this one and keeping it on it, or should I look for a Zenith? What are the pros/cons of either?

If it's got the 3 bolt throttle body, it's probably a Holley 94 from a Ford flathead V8- - - -239 cubic inches. Pretty good carb, and the calibration will be "close enough" to use on the 248. It's nowhere near the quality of the Zenith, but it's not a bad carb. I ran them on my 47 Mercury with a 255 cubic inch bored and stroked flathead and 11.25:1 compression.

The first 3 digits of the stamped engine number on the machined pad behind the distributor gives the cubic inch displacement of a GMC inline six- - - -228, 248, 256 (rare) , 270, or 302.
Jerry

Thanks for the input.
I ordered a model 94 rebuild kit so that I can clean it out appropriately. Going to pick up the truck from my property down south and bring it to my house this weekend… now for the fun of seeing if I can get it running and then finding wheels that won’t kill the neighbor kid if he looks at them wrong… hah I’m sure I’ll have more questions but for now that answers one of the many!

Works progress,

Make sure and check the SN as Jerry suggested before ordering any parts, all GMC’s look the same.

Ed

Ed,
Will do. As soon as I get it to the house I will knock The Who knows how old crusty grease off her and see what she reads!

I’m excited to get started on it! Now to find some replacements for the widow makers… what a nightmare that seems to be!

Thanks for your guys help! I’ll update here when I get a S/N off of the block.

Also, if it is in fact a 248, it does not have a starter attached… is the starter of a GMC 248 the same as one used in a 235 or is it a different starter altogether for the GMC engines?

Both the 1929-54 Chevrolet Master Parts and Accessories Catalog and the 1939-54 GMC Master Parts Book list part number 1107108 an available starter in 1953 (GMC has LOTS of starter options), si I'd bet they are interchangeable. I found new brushes, brush springs, bushings and starting motor drive (Bendix) at my FLAPS 5 years ago and did a poor-man's rebuild on my GMC starter. Under $15. DON'T use Emory cloth to clean up the armature because the abrasive dust left behind conducts electricity. Use regular sandpaper instead.

That "Holley 94" could be a Holley that was used on larger GMC trucks with 302 engines in the early-mid 50s. Would be an easy swap if you had the manifold too. What is the casting number on the manifold?

As both Jerry and Bill mentioned, look at the intake manifold.

Does the manifold have three holes for mounting the carburetor, or does the manifold have two mounting holes with a three hole to two hole adapter.

If it is a three hole manifold, and you like Holleys, go for it.

If it is a two hole manifold, and the carb is sitting on an adapter, don't do it!

Jon

I won’t have the truck home until Saturday from my other property, but the pictures I have show me that it has a three bolt carb, then there are what appears to be a couple of adapters stacked up that are for the vacuum lines (it’s a 2 speed rear end). One has a egg shaped cover plate facing forward… the tag on the carb says Holley, has 2328076 stamped into it, and also says what I think says LIST-660-1.

Just guessing- - - -once you have access to the truck, pictures will help- - - -that "egg-shaped" cover is probably a governor. Big rigs with 2 speed axles need to be protected from over-revving in the lower gears. I'm going to speculate that the engine might be a 270 or maybe even a 302. There were a huge number of military surplus 270's available dirt cheap after WW II, and a lot of trucks that were manufactured with smaller engines got retro-fitted with 270's during the 1950's and 60's. 302's came along in the 1950's as the biggest of the small and medium duty truck inline sixes. Unfortunately, hotrodders burned through the supply of surplus engines, and survivors are scarce and E$$$$pensive these days.
Jerry

I have some pics…
How do I post them? I don’t see a button to be able to attach them.

The valve cover has GMC stamped into it. That led me to believe it was a 248, but there is a spare cylinder head in the truck that has 302 casting numbers…

Holley List 660-1 was original equipment on a 1955 GMC 302.

Jon

Figured out the pictures! I’m learning the site.

She’s a little rough, but worth saving. Fairly complete. Used to belong to a guy that owned a sand and gravel business… my dad worked for him at 15 years old in 1969. This truck was one that he drove around and it had a dump bed on it.

Thanks Carbking!
I’m ignorant with these old big bolt trucks… vacuum rear end and all that is new to me. can anybody describe or point me to some literature on the Governor (if that’s what’s under the carb), as well as the other stuff under the carb?

I might have some service manuals that cover governors in general, but maybe not that specific one. Those Firestone RH-5 "widowmaker" wheels will need to be swapped for something safer before you put the rig on the road. They lock together with a tiny lip in the center of the wheel, and they're notorious for separating as the tire is being inflated. The wheels aren't simply dangerous, it's also illegal for tire shops to service them. If those rear hubs have 10 lug bolts, I need a couple of wheel centers (not the complete wheels) to use for a tractor project I'm working on, so please consider sending me a private message before you scrap them. Thanks!
Jerry

Yessir, I am just wondering how the Governor actually works and any quirks with making it work properly is all…
As for the widow makers, I’m aware. I think I posted on a previous reply that that was gonna be one of my hurdles is finding wheels that will fit to replace them with. I’ll let you know if I decide to part with them, but they WILL be replaced.

The same small diameter 10 bolt lug pattern is used on a lot of 19.5" tubeless wheels, but those tires look a little out of place on the older trucks because of the low sidewall profile. To make the rig a "roller" while you're working on it, you might check out salvage yards that have a few retired Class A motorhomes in their inventory. That lug pattern is pretty common on the bigger motorhomes.
Jerry

Here is a link to manuals on the governor:

Holley literature

Jon

Any plans for the Task Force?

Thanks for the link to the Carb books!

The ‘56 is next on the list after the ‘53 gets back on the road, but it’ll be a pretty extensive/expensive build.
I want to build a big flatbed for it that acts as a rollback truck to haul other cars on… but I’ll make the bed look age appropriate as much as possible. This ‘53 is just gonna be a Hay hauler/cruiser.

Also, thanks HotRod Lincoln for the thoughts on the motorhome wheels…. I see the P30 trucks seem to be a popular swap for axles/wheels among these older 1.5/2 ton trucks.

Got the truck back home today, and while cleaning out the seat high pack rat debris and such I opened the glove box to find the ORIGINAL ARIZONA TITLE!!! It says the truck is a 1951, not a 1953. It says the model is a 353-24C as I had originally expected, and it is a one owner vehicle. I will clean off the block casting numbers once I get it off the trailer and we will see if it is the 248 I expect it to be…
Also, I originally thought it had RH5 widow makers on it, but they appear to be 3 piece lock ring wheels…

I cleaned off the block numbers after we unloaded the truck today, and it is a 302!!!! The numbers on the block by the starter says 30267699…
Do the rest of the numbers mean anything or just the first 3?

Outstanding! Glove box contents usually end up being shredded mouse nest material. The rear wheels in your photos certainly look like RH-5's but they aren't very clear. The usual RH5 identifying features we look for are a flat raised area about 2" wide in the barrel section of the wheel close to where the center spider attaches to the barrel, and a solid bead flange without a lock ring on both sides of the rim.
Jerry

Have you looked at the engine number. The 3 bolt manifold was only offered on 302 engines. The three bolt will fit the 1952 270 engine that had the big port head, but the 270 engine was not offered with a 3 bolt carburetor. Your engine may very well be a 302 someone transplanted into it. Are you sure that it is actually a Holley 94. A Holly 94 had port vacuum which worked with the Ford Load A Matic distributors. However the 94 can be converted to run with manifold vacuum.

The carburetor on the right is a Ford Holley. The two on the left are GMC Holley

https://photos.app.goo.gl/huYaXYVgMown5nwR9

It really wouldn't surprise me if that isn't a 302 engine. Well, I now see in your last that it is indeed a 302. Anyway, take a look at the photos. I really doubt that you have a Ford Holley.

Fortunately these are lock ring wheels! Lucky there!
They do look like a RH5, but no split, and they are lock ring. If they match the fronts, they are 3 piece lock ring wheels.

Found it still has a PTO attached from when it was a dump truck too… might be handy to have for future attachments!

The engine turned over with a small pry bar on the flywheel through the starter hole pretty easily, so that’s a good sign!

So, now knowing it’s a 302, anybody have a part number for a 12V starter for this bad boy? I need one. It’s a 2 bolt starter like a 235, but I don’t know what tooth count it needs.

Also, I guess I need to start a build thread for this truck and quit posting everything under this one?

Before putting a 12v starter on it decide if it has the proper flywheel ring gear (168 tooth) for a 12v starter.

Do you have a 6V starter for it?

It currently has NO starter.
Is there any easy way to tell which ring gear it has? I’m guessing just start baring it over and counting teeth?

168 teeth = 12 volt. The 6V ring has 139.

I've been running my GMC 228 six volt starter on 12 volts for 40,000 miles with no bad effects. I'm careful not to leave it engaged long. It spins the engine over real fast!

Easy to bar over if plugs are out.

Ed

Distance between 10 teeth on a 168 tooth (12 volt) GMC flywheel is 2.363"

This one is from a '57 GMC 152 with a 270 engine.

Thanks Bill! Good idea!

Drop the dust cover off the bottom of the bell housing and mark one ring gear tooth with chalk or paint- - - - -then bar the engine over and count the teeth. 139 for 6 volt engines, 168 for 12V. The original engine would have been a 6V system.
Jerry

Quick math (assuming the OD of the 6v [139 tooth] ring gear is approximately the same as the 12v gear) computes to about 2.86" from tooth 1 to tooth 10. Yes, you still have to drop the dust cover, but much easier and less prone to a counting error that hand cranking the engine and counting each tooth for a full revolution.

While some may consider this post an exercise in semantics, I feel it is somewhat important.

The carburetor on your GMC 302 is NOT a Holley 94; it is a model AA-1, with a Holley List number of R-660.

The so-called "Holley 94" is also a model AA-1, and several different List numbers were used.

The main venturii of the so called "94" is 15/16 inch, which works out to 0.94 inch. A "94" is cast on the end of the carburetor, and for years ALL model AA-1's, many erroneously, have been called 94's.

The main venturii on the GMC AA-1 is actually 1 1/16 inch, so significantly larger than the "94".

Hope this post offends no one.

Jon

Good point, Jon. The 1955 Ford 272 V8 Holley with the 3-bolt throttle body also used a 1 1/16" venturi. When I installed one on a 239 cubic inch flathead V8 bored oversize .080" to 252, it was overcarbureted and had a nasty flat spot if the throttle was opened too quickly.
Jerry

Thanks for the reply gentlemen!

The carburetor does have a 1-1/16 cast into the side of it! That was a full on lesson on Holley carbs and that’s exactly the type of learning I am here for and my reason for being here. I am hoping the carb rebuild kit I ordered will fit it. It says AA1 on the box…

Thanks for the input! I like not only knowing the difference, but also why!

As far as the starter and the flywheel goes, it still has a 6v battery in the footwell box… I’ll crawl under it when I get some time and measure the section of teeth as suggested. I’m thinking that I may have a 6v starter laying around for a 235 that may fit this if I’m lucky… it’s just not a foot lever starter.. it would work for now if the flywheel is appropriate…

As long as we are talking Holley AA-1 carbs. I'm planning to use one on the 302 I have waiting for my '52 GMC. Here is Holley's spec sheet for the AA-1.