The Stovebolt Site Forums The Shop Area The HiPo Shop Almost a 261

Since 261 engines are pretty scarce and somewhat expensive when they do become available, how about this - - - - -let's make the much more readily available and less expensive 235 into an engine almost the same size- - - - -and maybe give it a torque advantage over the 261 in the process?

Here's my idea- - - -the same stroke increase that's available by offset-grinding the 261 crankshaft and using 292 connecting rods can be done with the 235 crank, and as an added benefit, the slightly shorter 292 rod will allow the original 235 pistons to be re-used with only a slight bit of machining to keep the pistons from hitting the cylinder head. An added advantage will be a piston deck clearance of zero- - - -not the lower deck height of the stroker 261 with the Cadillac pistons. If the 235 block is bored .080" oversize, the cubic inch displacement comes out to 257- - - -"almost a 261", and with a longer stroke to boot! For the really adventurous, there's a recycled NASCAR tool steel connecting rod that's available on Ebay pretty regularly that would allow an even longer stroke to be used by offsetting the 235 crank journal further than is available by using the 292 rods. I haven't done the math on that one yet!
Jerry

LOL!!

Jerry, you're always trying to find a way to reengineer the wheel, or in this case, the engine. Don't get me wrong, I love what you're doing. Keep up the good work.

I am willing to bring my truck over if you want to test your engine when it’s completed!

Well, I did the math- - - - -the NASCAR connecting rod allows a stroke of 4 3/8" instead of the 4 1/8" that's possible with the 292 rod, but the 235 piston is too short to work well. I'd need to find a piston that's 1/4" taller between the wrist pin and the top. I think I've figured out a work-around for that, at least for a short-life prototype engine to do some dyno testing with. If the numbers look good, custom pistons could be made, but that increases the cost of building the engine considerably. One dimension that would need to be monitored closely would be the clearance between some of the rods and the camshaft, but I don't think that would present a huge problem, even if a little extra clearance had to be ground into the cam between the lobes. There's already a flat spot there on the cam core.

A 235 bored 60 over with a 4 3/8" stroke comes out to 270 cubic inches! That one ought to have enough torque to pull stumps- - - -of Sequoia trees!
Jerry

In the interest of healthy debate; what would be the advantage of going that route versus tracking down a usable 292? I'm way out of my depth here so be gentle. :-)

No Larry, Nooooooo.
Just messin'
For me, the 216/235/261 look is too iconic to go with a 230/250/292. If I were to go away from the 216/235/261 (and I have), I would go with a small block V8. Going with a 350 is not any more work than going with 292. A 235/261 is a direct bolt-in.

Larry, the main advantage is having an original-appearing engine compartment and not having to modify motor mounts, bellhousing, driveshaft, etc. An added advantage is being able to outrun/outpull all your buddies with a "stock-appearing" engine that doesn't need to turn high RPM's to do it. Stroker engines put the power where it does some good- - - - -low and midrange RPM's. The stovebolt cylinder head design pretty much makes high revs impossible, so putting a grass-cutter stroker in there makes a lot more sense.

The round track racers have a saying- - - - -"Horsepower is good to brag about, but torque wins races!"
Jerry

Or "Horsepower is how fast you hit the wall; Torque is how far you move the wall"

SimS

What diameter and height piston would you need for this setup? Last time we had this discussion, I remember searching some different things that were pretty close to the right dimensions (either too tall or too short).....but that was based on the 292 rod length.

I'm working on a modification to the 235 piston that involves moving the wrist pin lower in the piston with an offset bushing. The NASCAR rod has a smaller diameter wrist pin than the stovebolt rod, so a bushing would be required anyway. By opening the pin bore up to 1" diameter and offsetting the new pin hole in a bronze bushing toward the bottom, the piston comes closer to the top of the cylinder. I'm in the process of machining such a piston now. If a prototype engine with that setup survives dyno testing, a custom built piston with the proper compression height could be commissioned.

The ideal piston for this application would have a 3 5/8" bore and a compression height of 2 9/32" (2.281") The wrist pin diameter of the NASCAR rod is 0.787", but that can be dealt with by putting a bushing into the pin bore of a piston with a larger pin hole. I'm adapting a set of 305 Chevy pistons with a .927 wrist pin to that same size rod by making bronze bushings for the pistons.
Jerry

How about a jig to Re-sleeve lifter bores while you're at it? Jesel or Chrysler style lifters may be a good alternative.

That wouldn't be a difficult conversion- - - -just use an ACME thread jackscrew and an air impact wrench to press an undersized sleeve into the bore. Getting one machined that would shrink to the right diameter when pressed into place would take a little tinkering to avoid having to bore or hone the sleeve after installation would be the tricky part. On hydraulic lifter blocks, the position of the cross hole would be critical. A dingleberry hone like one for brake cylinders could be used to do the final fitting for a good slip fit with minimal wobble.
Jerry

Did a bunch of googling and looking at different piston options last time we talked about doing the "Cadillac 261" stroke job on a 235.

My googling skills have let me down today. But I remember looking at the early Toyota 6 cyl (2F, I think) and seeing some commonalities. If memory serves it was about the right bore, but maybe a bit too short or too tall on the compression height. And now I can't find the dimensions again. And then again, I might just be misremembering completely.

Since the original Toyota Land Cruiser engine was a virtual clone of a stovebolt, that doesn't surprise me. Those parts are getting pretty scarce and expensive, however, since far fewer of them were produced than 235's.

Hmmmmm- - - -that 2F is an interesting engine- - - -4.2 Liters (256 cubic inches) and brand new (not rebuilt) carburetors on Ebay are less than $100.00. They're progressive linkage 2-barrels with a manual choke and vacuum operated secondary barrels. That sounds like an excellent option as a replacement carb for a stovebolt with an intake manifold modified to accept a single 2-barrel.
Jerry

Yeah, the fact that they’re a pretty close copy is what set me to looking in the first place. Wish I could find the dimensions. Now it’s bugging me.

Gmc 248 piston is a bit too fat and a bit too tall.
https://egge.com/part/egg-1000-l2021-6/

Don’t seem to be a lot of pistons with that much compression height. At least not common ones.

My brother-in-laws' family collected Toyota Land Cruisers.

Some had engines that looked like 235s, and some had engines that looked liked 230s/250s.

Jerry, how much does a set of custom pistons cost?

I did some poking around and found a couple things that might work for you (based on specs you gave to match with the NASCAR rod) with some modification. But they aren't exactly cheap.

Packard piston - thttps://egge.com/part/egg-1000-e152-8/
The overbore options get you into the range of a 235. Not enough compression height. Could you cheat that much out of the crankshaft offset grind to compensate?

Flathead Caddy piston - https://egge.com/part/egg-1000-e107-8/
Again, the overbore pistons gets you into 235 range. Closer on the compression height. Not sure how that chamfered top would affect compression.


John Deere 2010 piston? - Don't have the part # handy and couldn't find a compression height. But it's 3.625 and certainly looks like it might be "tall" enough. For that matter, lots of old tractor pistons have a taller appearance (comp height seems to be the tough part of the match, most auto pistons are shorter)....and there might be something out there in the tractor world. I haven't found any literature that lists the specs.

Custom pistons tend to be pretty pricey, and the tool steel rods from Carillo, Pankl, etc. are over the moon! There are several sellers on Ebay that recycle slightly-used engine parts from NASCAR race teams. Those parts are generally around 10% of their original cost- - - -a set of $2K rods for $200.00 or so. They use a very small rod journal, which allows a crankshaft to be reground way off its original centerline, increasing the stroke. Flathead Ford hotrodders were doing the same thing 60 years ago, using 85 HP engine rods to increase the stroke of the 4" Mercury crankshafts to 4 1/8", or even 4 1/4" by doing a little welding on the rod journals. We made 3 9/16" strokers for 350 Chevy engines the same way- - - -using 2" diameter rods for 283 engines and grinding the 2.100" crank journals a little off-center. The rods I'm looking at are 6.450" long, with a 1.850" crank diameter. That allows the stroke to be increased from 3 15/16" to 4 3/8" by offset-grinding the center of the stovebolt crank journal, and creating a shoulder that keeps the narrow rod centered, like the "Cadillac" stroker does with the 292 rods. It would take some creative machining, but that long stroke should make ridiculous amounts of torque. Increasing the old flathead's stroke by 3/8" made then torque monsters, especially when running 11:1 compression on alcohol!
Jerry

long stroke is really helpful! When my 1950 DeSoto died in Montana years ago, we found an engine out of a combine (mopar flathead 6!) that had 30 more cubic inches (265 instead of 235) and it was all stroke. That was fun on gravel roads!

I had a 51 Chrysler business coupe with that engine my senior year in high school. Once I figured out a way to lock out the fluid drive and get the power to the transmission without a lot of slippage, it became a fun ride!
Jerry

Well, boys and girls- - - -I am now the proud owner of a modified 292 connecting rod! By adding a bolt-on spacer to both sides of the rod cap, the rod will center up on the 235/261 crankshaft journal without doing that Rube Goldberg-looking stepped down crankshaft regrinding job. The spacers are machined from a big flat washer which is cut into two pieces, and they are attached to each side of the rod cap with three flathead screws, and machined and ground to the proper width. Since the only function of the spacer is to center the rod cap in the crankshaft journal, nothing needs to be done to the rod itself. The spacers are approximately .100" thick, which makes the rod cap the same width as a 235 rod. Just regrind the rod journal to 292 size, and offset it to make the stroke 4 1/8". With a 60 overbore, the 235 becomes a 255, and the compression goes up about one ratio. "Hello, torque!" Now- - - -just gotta do the same thing five more times! I haven't decided yet if I'll need to do a little low-temperature silver soldering to make sure the spacers stay put. If I was planning on building a high-revving race engine, definitely- - - -but since the whole purpose of stroking is to increase low-RPM grunt, doing a bunch of high-speed stuff is sort of pointless.
Jerry

Low rpm grunt sounds good.
While out on my usual Sat cruise I always hit a spot where I have to slow down for a curve then start up a moderate incline. The 216 grunts but just doesn't have that "low rpm torque" to make it all the way to the top, which necessitates a upshift to 2nd.
A good low rpm torque monster could possibly do away with upshifting all together LOL. Keep pushing those envelopes, shame I've already got my 235 built.

Disclaimer: I can't think of any good reason why anyone would do what I am about to describe. Maybe to retain an original looking engine, with some significant "hidden" performance upgrades, in a very original truck. I'm not sure that would qualify as a good reason. Just having a random thought.

Jerry has demonstrated that it should be possible to apply this "stroker" concept to a 235 with the 292 rod.

Could the same thing be applied to a low pressure/dipper 235 with some modifications to the rod? I'm not up on all the journal dimensions and how the dipper actually affixes to the rod cap.

Changing the stroke on a dipper engine would involve some major re-engineering, as the height of the dipper troughs and the angle and position of the spray tubes would have to be altered. Chevy service departments had a whole bunch of measuring tools and nozzle-aiming jigs back when these engines were daily drivers, and the minor stroke change between a 216 and a 235 required a different oil pan, and different setting gauges. The dippers are stamped sheet metal items that bolt on between the rod nut and the cap. One sneaky trick that I've seen used occasionally was to use a tapered punch to widen the dipper so the oil from the squirter tubes had a bigger target to aim for. The troughs are only used for lubrication at idle- - - - -once the RPM increases, the dippers actually intersect a stream of oil that's shot across the pan near the bottom of the stroke. If the squirt tubes aren't aimed properly, the oil stream can miss the dipper and cause a bearing to fail at cruise RPM- - - -bad juju!
Jerry

Yeah, scratch that.

I was thinking mostly about getting the dipper on the rod and having the right hole to get oil from dipper to the bearing. Forgot about the stroke changing the relationship to the trough.

The conversion I'm working on to put Massey-Ferguson tractor rod bearings in stovebolt Babbit rods will require drilling a couple of holes in the bearing to match up with the dipper hole and the spit hole in the upper section of the rod, and possibly machining a shallow groove in the middle of the bearing. The advantages will be much lower bearing cost, and the ability to salvage "worn out" .030" undersized crankshafts.
Jerry

OK- - - -I re-ran the numbers- - - -It looks like the 4 1/8" stroker modification to the 235 works with NO piston alteration whatsoever, and the piston will end up .011" below the top of the block, closer than it is on even a stock stroke 235. The 292 rod is just enough shorter than the 235 rod that it keeps the piston from sticking out the top. Here's a comparison:

Stock 235:

Piston compression height: 2.035"
Rod length: 6.813"
1/2 stroke:(3 15/16 stroke) 1.969"
Original block height: 10.969"
Piston below deck: 0.057"

Stroker 235 with 292 rod:

Piston compression height: 2.035"
Rod length: 6.760"
1/2 stroke: (4 1/8" stroke) 2.0625"
Block height: 10.969"
Piston below deck: 0.0115"

All that would be necessary to make everything fit would be to put a bushing in the piston end of the 292 rod to accommodate the 235 wrist pin! Teflon or aluminum buttons in the ends of the pin would make it full-floating, and eliminate the need for any sort of wrist pin locks.

Jerry

Dumb question:

Does the stroke change necessitate any adjustments to valve timing? I'm assuming as long as the offset crank grind is indexed properly....TDC is still TDC.

No, changing the stroke only affects displacement- - - - -it makes the engine a bigger air pump and increases the compression somewhat due to more cylinder volume being squeezed into the same combustion chamber. That would allow a slightly more radical cam to be installed, (like the Corvette/261 cam) but it doesn't necessarily have to be done.
Jerry