The Stovebolt Site Forums The Shop Area Engine Shop Working Truck Engine Choice

Hey guys! It's been a while since I've posted, but I've got a 1951 2-ton Chevrolet grain truck that I still use on the farm for hauling wheat in the summer and fall. Been in the family since nearly new. In 2018 I adjusted the rod bearings, and none of the shims are left. I was hauling grain this fall when it developed a rod knock so I've got it in the shop for engine work. I think I've got three options, and I'm trying to decide which to pick.

1. Keep and rebuild the original 235 dipper cup engine. I like this idea because I'm a purist (for the most part) so keeping the original engine appeals to me, especially since everyone says the dipper cup engines don't hold up over time. This one lasted 70 years and 93,000 miles hauling 18,000 lbs of grain in every load, and even hauled combines to North Dakota and back to Oklahoma 7 or 8 times. So I'm fairly convinced they hold up.

2. Find and rebuild a full-pressure 235. Most would say this is the best thing to use for longevity under high load conditions.

3. Find and rebuild a 261. I like the idea of this, just for the extra power. Not that the 235 is underpowered, but a little more power never hurt anyone.

Just curious to see what others' opinions are, or any other recommendations.

People also say to drop in a 350, which I know would be cheap and be a horsepower boost, but as a guy told me once, "A 350 is a bellybutton engine...everyone has one". I'd kinda like to stay with the inline 6.

Thanks!

It would depend on how far from "original" you're willing to go. The 261 would be almost a drop-in fit, depending on which year of engine you can find. A 54 or early 55 261 will even have the correct water pump position, while the late 55 to 62 engines will need a relocation plate to use the 216 style high mount pump. The flywheel, clutch, and everything on back in the drive train won't change at all. If you're willing to do a bellhousing and center crossmember swap, plus some front motor mount tweaking, you could even fit a 292 in there. Have you inspected the early 235 crankshaft from the knocking engine yet? If it's still round and isn't scored, a swap to a new set of rods will put you back on the road with a simple engine rebuild. There are still plenty of reconditioned Babbit rods out there- - - -I can usually find several sets on Ebay, both standard and undersized, at pretty reasonable prices. Building a spray-oiler engine isn't terribly difficult once one gets past the "Babbit rod" mystique. Scrape-fitting the rods for a good fit and setting the oil clearnce with shims isn't rocket science-- - - -some of Dad's mechanics in the 1940's and 50's could barely read and write, but they knew how to fit rods!
Jerry

I have not had the crank out for inspection yet. I spent this weekend removing the transmission, in two weeks when I get back to it I'll lift the engine out and begin disassembly.
Would it be possible to line bore the block and rods to do away with the shims? I know that's been done on most similar-era farm tractors that used shims on the mains and rods.

As far as getting away from original...I'd like to keep the foot starter, so would that rule out the 292?

There's a set of insert-type rod bearings that require boring and honing the rods that eliminate the shims. Then the crankshaft is precision ground to fit the bearings with the correct clearance. The problem with that is that the conversion bearings are getting scarce and expensive. A friend who runs a specialty machine shop claims that .020" undersize bearings are impossible to find, and 10 and 30 under are getting outrageously costly. IMHO, I don't remember ever seeing a standard diameter conversion bearing. Egge Machine will sell you conversion rods and bearings but your checkbook will need CPR after dealing with those folks!

I use a different procedure to eliminate the Babbit bearings in the spray oiler rods. The rods can be machined to accept a very inexpensive bearing for a Perkins 3 cylinder Diesel engine that's used in several small Massey-Ferguson tractors and similar pieces of equipment. The bearings are less than $10.00 apiece. Then regrind the crankshaft .060" undersize to fit the standard size Perkins bearing. Since the crankshaft is solid with no drilled oil passages, regrinding that small doesn't hurt a thing. Any automotive machinist worthy of the name should be able to do that. There are plenty of main bearings and adjusting shims available, so there's no need to line bore the block. I also machine the back of the block for a full circle lip seal to eliminate the leaky and troublesome rope seal. A spray-oiler engine isn't some sort of boogeyman- - - -remember that we won WW II with untold thousands of trucks equipped with them!

A "fake" foot starter can be made by mounting a push button starter switch for a Farmall cub tractor to the floor and attaching an original pedal button and rubber accordion boot to it. Use that switch to energize the 292 starter solenoid. Also- - - -brand new 292 combine engines can be purchased form a supplier who gets them from a factory in Mexico!
Jerry

I have an engine identified by a member here as follows:
That's a 235 made between 1957 and 1962 for the passenger cars with 3-speed transmissions.

T = Tonawanda Engine Plant
8 = Month (August)
06 = Day
A = Regular 235 for passenger cars with 3-speed transmission

There is a tag attached to the block that indicates that it has been rebuilt in the past, bored oversize, crank ground, etc.

I never ran the engine but was told that it ran.

I don't know that it is worth anything but you can have it if you want to come to Wisconsin to pick it up.

Jerry, when you use the Perkins bearings, do you bore and hone the rods to eliminate the shims as well?
Personally I kinda like the idea of the line boring the block just to get away from the adjusting shims, but is that method prone to having problems?

WICruiser... I appreciate that offer! However, Wisconsin is a pretty good stretch for me, so I believe I will try digging into my engine first and see what all it needs.

I just checked Ebay- - - - -search "216 Chevy connecting rods" and you'll find a bunch of them listed. 216 and 235 rods interchange since the stroke difference on the 235 is compensated for by the taller engine block. There are also conversion bearings available there at a killer price- - - -just over $100.00 a set. Every size BUT .020" undersize, including STD, .001 and .002 under. I just might scavenge up a couple of sets at that price while they're still available! The 1937-47 rods can be fitted to the 48-53 engines by narrowing the big end width to fit the crankshaft journal. Chevy went to a narrower rod in 48.

Now, here's a bit of trivia- - - -a set of WAY undersize Babbit rods like .030 or .040 under can be honed to a bigger size on a Sunnen hone. If you need 20 under, for instance, a set of 30 under rods can be honed to the bigger size. I've also figured out a way to put a 250/292 oil pump in a spray oiler engine, which will flow close to twice the oil volume of the smaller pump. You could have a real oddball that way- - - - -a spray-oiler with real oil pressure!
Jerry

Yes, I have a fixture that mounts to the carriage on my lathe and I bore the rods to a close fit for the insert bearing with a precision boring head in the spindle, then finish-size it with my Sunnen hone. I drill a hole in the bottom bearing to line up with the dipper cup hole in the rod cap. Since the main bearings are already insert types, using the shims allows the oil clearance to be adjusted to a minimum, and readjusted for wear if necessary. Most machine shops absolutely refuse to try to line bore a stovebolt engine since there are four different size bearing bores. I have a portable line bore machine that bolts to the oil pan rails which makes the job a lot easier- - - -set up four cutters and do the job with one pass, but old geezers like me who are willing to do that are getting harder to find every day. I can either convert the rods to fit the original style insert bearings or the Perkins bearing- - - -it's the same amount of machine work either way. Drop me a PM for more details if you want to- - - - -the moderators get their drawers in a wad when people try to do business on the open forums.

Edit- - - -another sneaky trick when rebuilding an early 235 is to replace the cast iron pistons with 54-62 235 aluminum pistons. They're a drop-in fit, and the lighter pistons don't hammer out the Babbit bearings as quickly. The engine also accelerates better with the reduced reciprocating weight. It's not even necessary to rebalance the crankshaft since an inline six is inherently balanced to begin with, regardless of the weight of the pistons.
Jerry

If you intend on keeping this truck a few years you might consider sorting out the install on a 56 and up motor. Particularly if you can find a good running example. No shims, neoprene rear main seal, improved oiling, little little higher compression, easier to find parts for, more power.

People also put Pinto overhead cam 4 cylinders in Model A's- - - - -mostly because they don't have the skill or the incentive to do things the "right" way!
Jerry

At first I thought about just building a 235 to the Corvette specs to get 140 hp out of it but it seems some of those parts are pretty pricey and hard to find.
I would like to get an 848 head but I don't think those will work with my early model engine.

That is why you might consider a later 235. All of the passenger car 235 motors from 56 through 63 were specified for at least 140 hp. None ever actually came up to that specification but they were and remain very good reliable runners. Car motors have hydraulic cams and lifters, neoprene rear main seals, no shims on the bearings, precision main bearing and rod bearings, full pressure oiling to the motor, 848 head for higher compression, improved oiling, all that in a package that most people would not recognize as a later motor in your truck.

Can you rebuild a splash oiler and get another 90K, quite possibly. And that is what you might like to do. But in terms of getting a little more bang for the buck, the later motors are the ticket I think. They are in fact the last evolution of the 235 that Chevrolet had been steadily improving with the last improvements coming in 59 or so. Its a hard call I know. Maybe the better question is going down the road a few years, which motor will be easier to maintain and get parts for, which will work better for your needs. I dont think there is a wrong answer here. Your gut will tell which way to go.

I wish my 258 cubic inch "216" was a little closer to being ready to run. Hauling the kind of load that truck does would work better than anybody's dyno run to give it a workout! Doing a basic rebuild on the spray-oiler 235 for now, and building up one of my 290-something cubic inch 261's with a 4 3/8" stroke for later on might be a good option. That one's going to have H beam connecting rods rated for 600+ HP, and around 9.5:1 compression.
Jerry

Boy, if you build that 290 cube motor I would happily copy the build, lol. What do they say, Imitation is the highest form of flattery. I still have one more unmolested 261 block waiting for an adventure

The same basic approach can be taken with a 235, but the displacement tops out somewhere around 270. Same long stroke, same rods, just a somewhat smaller bore size. The head would probably need a little milling to get the compression up where it needs to be. I really detest domed pistons- - - -they mess with the flame front travel across the piston crown and create hot spots and pressure spikes that lead to detonation.
Jerry

You have my attention sir and I am all ears for both as I have a couple of 235 motors also looking for new adventures. That, and to be able to get a 6 into the 270 cube arena without having to hunt down a 261 block, that is a real benefit.

Some of my off the wall ideas are a result of growing up around a race engine shop in the early 1950's where doing things like offset-grinding crankshafts and relocating cylinder bore centers was just a matter of course. That must have made a lasting impression on me. The old flathead Ford V8 could be bored 1/4" oversize by someone who knew what he was doing, and a 1/2" increase in stroke length was done routinely. A 239 cubic inch engine could go to 300 or so without a great deal of effort. Welding or brazing material into the combustion chambers could get the compression up into the 11:1 range, and methanol plus some oxidizers was the fuel of choice. The lobes on an Iskenderian "404" camshaft looked almost square, with a big flat area at the top, and they used a special radiused bottom lifter that required block modifications to keep them from rotating. No, those engines didn't last long, but the ran like they had a demon chasing them! They also did all that on only three main bearings!
Jerry

These are some really neat sounding ideas, getting that many more cubic inches out of a 261 and 235.I'm working on learning more about the machine work and the precision instruments for getting everything exactly right. I feel like right now I know just enough to be dangerous, and I put too much faith in machinists to get everything right for me to assemble. Especially on the "non stock" things.

I've heard of people boring out Ford model A engines (they're basically half of the flathead V8, right?) to fit Farmall M tractor pistons, which I believe have a 3.8 or 4" bore. Not sure how long they lasted, but heard they made a fast coyote hunting wagon.

You make a good point here. My gut tells me to rebuild my spray oiler. Now whether that's a stock rebuild or do something like Jerry's talked about with a larger bore and longer connecting rods, etc...I haven't decided yet. I don't know if a spray oiler would be a good candidate for that, simply because of the extra stress placed on the bearings and lack of full pressure lubrication.

Question for anyone: Is it true that Oldsmobile/Buick/Cadillac engines of the same time frame had pressure-lubricated rods?

Chevy was way behind the times with their 216/early 235 oiling system. The Ford flathead in 1932 had pressure lubed rods, and so did Chrysler's flathead sixes in the 1930's. Charles Kettering designed the Olds/Cadillac OHV V8's that came out in the 1949 model year, but I'm pretty sure Olds, Cad, and Buick had more sophisticated oiling systems in their previous line of engines. Changing the stroke on a spray oiler isn't impossible, but I won't be doing it!

There's nothing really wrong with a spray-oiled engine, as the faster it runs, the more force the oil has to enter the dipper cup on the connecting rod. The only time the "dippers" actually feed from the troughs in the pan is at idle when there's not enough oil volume from the spray nozzles to reach the middle of the crankcase. Just keep the bearing clearances adjusted right and the old style rods will outlast insert bearings. Original equipment GM Babbit alloy is as hard as woodpecker lips- - - - -it dulls a high speed steel cutter bit when I'm machining rods for insert bearings. Reconditioned rods usually have a softer alloy bearing material than OEM rods.

Fun and games!
Jerry

I think the shim-for-clearance concept is pretty cool. But doesn’t shimming (or removing shims) make the rod journal something less than round? I guess it’s not enough to matter?

The Babbit isn't completely round to begin with- - - -there's a tapered area on both the rod and the cap at the parting line that's a few thousandths bigger. (just like an insert bearing- - - -they're not round either, where the soft metal meets the crankshaft). Bolt up a connecting rod with a bearing in it off the crankshaft sometime and do some measuring.
Jerry