The Stovebolt Site Forums The Shop Area Engine Shop Repowering an AD 1 ton

I have been running a 235 in my 3800 for many years and for the past 20 yrs it's carried a camper and lately pulles an 8,000 lb trailer. It's got an SM420 and a Spicer 3-speed brownie. It's been hopped up to what I feel is the max for a reliable road engine. It has a lot of miles on it but runs well. But it's pretty slow on the hills. It'll now just keep up with loaded log trucks on the hills. Rebuilding a 261 doesn't seem like enough bang for the buck.

Other than a 261, the most popular option seems to be a small block Chev V-8 and I'd be starting from scratch except that I have a SM465 trans, Aluminum bell housing flywheel and clutch. There is a bell housing on craigs list that the seller says is for tri-5 chevys. The picture shows angled motor mount pads. Being that the truck is constantly run loaded I'd like to keep the factory cross member. I read the Bell housing tutorial but it's not clear if the angled bell housing will work in AD trucks.

Questions:

1) Any better options for engines than a Gen I small block?

2) Will an early small block bell housing save the cross member?

3) Anyone got a set of the 265 exhaust manifold that'll clear the steering gear?

The 465 has a bigger shoulder on the input bearing retainer, which requires a bigger hole in the bellhousing. I doubt if the tri-5 V8 housing will accept the 465 trans, but the 420 you have behind the 235 will handle anything except a beaned-up big block V8, IMHO. You'll need a 3-bolt starter nose cone that bolts to the bellhousing, not the block. I believe any truck crossmember from 1954-up will have the angled mounts. You might want to consider a 400 small block engine- - - -it's got a longer stroke and more torque than a 350, and as long as you run enough radiator and keep it cool, it's very reliable. The exterior dimensions are the same as any other small block engine, and the 265 exhausts should bolt right on, as well.
Jerry

Hy 1Ton_tommy if you can locate a transmission crossmember from a 1954 or 55A and swap that into your chassis that will give you the angled mounts you need for the V8 bellhousing and keep your chassis basically stock, hope that helps.

With some fiddling with front motor mount and radiator mounting you can run a GMC 302 six cylinder, and bored a little over is even bigger yet.
I think less work to install than a V8.

I have a complete 1954 3pc Hydramatic crossmember if that will work for you.

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When someone advertises something for a tri-five it is generally for a 55-57 car. They look similar physically but the truck mount positions are different. A bellhousing from a 55-59 V-8 and 63-67 V-8 and 6 cylinder trucks will work with a SM420 transmission. (60-62 use a hyd clutch slave cyl and are different). A 68 to 72 truck bellhousing would have the larger hole used for an SM465.
Fred

One can also easily bore out the 465 retainer diameter to 5.125"

Ed

Thanks for all your informative comments. I really appreciate it.

I suppose the choice of transmission depends on what bell housing I can find.

What is the difference between the car bell housing for the tri-fives and the truck housing?

Can I cut and weld a little on the existing cross member and use the truck bell housing? I'll PM Yellowsub about his cross member if that'll really work. I only worked on one hydramatic six and that was forty years ago so I don't remember much about it.

Using the SM465 would save me overhauling the SM420 but would create some additional headaches, like boring the bell housing If I can't find a later truck housing but more than that there is the e-brake ratchet bolted to the side of the 420. On the other hand maybe it's best to bore the bell housing to ensure concentricity with the pilot bearing. That would mean using the 465. I've read that some BHs are a long ways off from the factory and then when you start swapping BHs and blocks it compounds the problem. I may have that problem now as the input bearing on the 420 is noisy after about 100K miles.

I haven't looked closely but I don't think the 465 has bosses for the e-brake lever. Plus I'd have to rework the brownie linkage as it's bolted to the 420. So if I can use the 420 that sounds like the way to go.

My whole project is complicated by the disappearance of auto parts stores. There are now no full line jobbers in north Seattle - Not even NAPA. They all closed up. My favorite parts men have all retired and the countermen now can only look up something by application. So it's up to me to know what year/model various parts were used on. Try asking the computer jocks for a series 1320 u-joint and you'll come up with a blank stare. Sigh.

I re-read Fred's post so the car/truck bell housing question is answered. Thankyouverymuch.

Grigg, I have toyed with the GMC idea for years but parts for those are rare as hens teeth when you're on the road somewhere. We got stuck on Escalente, Utah this fall with a 98 Suburban and had to wait four days for parts (fuel pump). The hiking and weather was good though.

I'm trying to get far away from electronics and use field-reparable equipment. The 98 Suburban is not that. The 51 3800 is; though it's noisier and more work to drive. The 235 setup was great for years as NAPA had anything you might need; like ignition points in Dawson City, Yukon -- in stock. No more. That was 1999. The Suburban is now bedeviling me with its PassLock security system. What it we had been 50 odd miles down the gravel, dead-end Hole In The Rock Road when the pump crapped out. There's no work-around for that or the PassLock and it's a long walk back. We actually did go down that road and nothing bad happened till we got back to Escalante. Whew!

My choice would be the inline 292 motor, bolts up to all the V8 tranys, lots of power and easy to get parts for. My limited experience with GMCs while a great motor the heads on most are cracked and hard to find.

Best of luck

I am building a 1949 1 ton dump bed with a gmc 302 and the 4.11 from. 67-72 Chevy truck. Retaining the 4 speed and hope it will all come together. Will take my chance with the 302 as it is a totally rebuilt motor in a crate coming from an army surplus warehouse. I suspect though I will still fall behind the logging trucks on the hills around here.

Since you are always hauling loads, an NP-540 series 5 speed trans will be more useful, no matter what engine you use. Looks just like a 435, just 4 shift rails, OD version while rare, has a big gap where they put the OD, not very useful with a load.

Ed

I think I'll start collecting parts for a V8 swap.

Seems like the place to start would be that 54 Hydramatic cross member. PM me if you've got one.

Then a bell housing, starter to match. Flywheel has to match the motor, I've read. The change came in 86? Right? Any downsides to using a 86 or later small block? I don't want something I can't use carburation on. I suppose I should buy a small block interchange book. Can anyone recommend a good one?

A 400 small block would suit your needs to a "T" IF you can find one that will clean up at 0.030. They just can't take much overbore. A second option is a 377 or 383 stroker kit which one can find on ebay for as little as $400. This gives the longer 400 stroke in a much easier to find 350 block. For your app a cam that was near the same specs as the the one for a 366 big block would work good---all low rpm torque. IIRC (no guarantee) I turned some front bearing retainers down to fit the smaller bell housing hole. Had to use socket head (Allen head) bolts that may have been shaved a bit. You just need the left side 265 manifold. With the flat log type exhaust a 2bbl carb would handle all the induction one needed. A Rochester from a 455 Pontiac or Olds would work good and are reliable with easy to find parts. Our tow vehicle for years was a 51 GMC with a 500 Cadillac engine and it was great so I know big cubes and a long stroke works. The V8 choice for you is the right one in my opinion.

One can also easily bore out bellhousing to 5.125" to fit larger retainer.

Ed