The Stovebolt Site Forums The Shop Area The HiPo Shop 247 cubic inch 235- - - - -

Here's a modification that just about any machine shop can accomplish on a 235, with modern parts and a crankshaft that might be considered "junk" for a conventional rebuild. A big block Chevy V8 runs a connecting rod bearing that measures 2.200", considerably smaller than the 2.312" stovebolt rod bearing. Those "worn out" 235/261 crankshafts that have been reground .030" undersize and worn out again can be reground to use a big block V8 connecting rod and bearing, and there's a custom length BBC rod that's 7.1" long. That rod, and a crankshaft that's had the stroke changed to 4" instead of the original 3 15/16", plus a set of 92MM pistons for a Japanese diesel engine can be massaged together to get 247 cubic inches, a pretty good compression increase, and the engine still looks completely original from the outside. "None of the above" is a drop-in fit, but it's pretty much routine work for anybody with the unmitigated gall to call himself a "machinist"! Another option instead of the diesel piston for the same setup would be from a 223 cubic inch Ford inline six, produced from 1952 to 62. Both pistons are approximately 3 5/8" bore, and they're almost exactly the right compression height to work with the above rod/stroke combination with just a little bit of tinkering on the wrist pin diameter and compression height.

There's also a 96MM diesel piston with the same design that will work on a 261 stovebolt. With a 4" stroke, that one gets 269 cubic inches. Pistons for a 265 Chevy small block V8 will also work with that rod/stroke combination on a 261. With a 4.25" stroke, a flathead Ford V8 connecting rod, and a .060" oversize 265 Chevy piston, the 261 gets all the way to 291 cubic inches!
Jerry

The same 4" stroke crankshaft/big block Chevy connecting rod setup can be installed in a 216 engine by narrowing the thrust bearing web to 235 dimensions, and using pistons for a Ford 170 cubic inch 6 cylinder engine. With a .060" overbore, the "216" becomes a 237 cubic inch, and has full pressure connecting rod oiling.
Jerry

Jerry,

Would you comment on a couple of aspects of such a rebuild:

1. Projected torque increase (not expecting specific ft-lbs, just general terms i.e., mild torque increase, significant, pull your house around the block ...)

2. Durability. If we're whittling metal off, how would this impact this engine's ability to stand up to the average (whatever THAT is ...) use we Stovebolter's make of our rebuilt engines in our driver trucks? Will our grandson's still be driving this engine 20 years from now? Does this increase fragility or can the good ole 216 block take it?

3. Your idea of who would be interested in this sort of a rebuild -- Somebody like Otto (hard driving all day every day around the the Atlanta beltway) or NAPCOMan (preserving the original but worn out engine to get the truck on and off the trailer as you collect AACA trophies) or someone inbetween (most of us ...keep the original engine but be able to cruise comfortable in modern traffic and not have to rebuild the engine again within our lifetimes)?

4. Projected costs. To me, if you're going to rebuild an engine -- especially a babbitted 216 --- parts is parts and you're going to pay for machining and part anyway. Your projected build seems to involve replacing unobtainium parts with more readily available, perhaps even "Off the shelf," parts ... parts may even be less costly your way? Machine shop bills would probably be a wash -- roughly similar either way?

All in all, I think we have a really cool tech tip here.

John

All good points, John. GM inline engines (not just stovebolts) such as GMC, Buick, Pontiac, and Oldsmobile from the late 1940s and early 50s were all massively over-engineered. For instance, those main bearings that get progressively larger toward the flywheel end of the engine turned out to be an unnecessary, and expensive method of getting the job done, plus they added an exponential level of difficulty to a complete rebuild. Ditto for the connecting rod journals- - - - -they're way oversize for the job they need to do. Changing main bearing size is doable, but it involves machining operations that most shops either aren't equipped to do, or they just refuse to because of the labor time involved. Changing stroke and rod journal size is a much simpler job that only involves one machine- - - -a crankshaft grinder. Stroker engines have been around for many decades- - - -my father was doing it on flathead Ford dirt track engines in the early 1950s. By reducing the size of the connecting rod journals and offsetting the centerline, more stroke (and torque) can be built in- - - -sometimes a LOT of it. There's also a small, but significant reduction in turning friction with the smaller rod bearings. The 1/16" stroke change involved in the engines I have described above increases torque- - - -it won't be massive, but it should be noticeable- - - -especially on the 216. The primary advantage is to enable the use of decades-newer, new, not reconditioned parts like the big block Chevy connecting rods. Also, manufacturing tolerances and metallurgy have improved pretty dramatically since the 1950s. Modification of other internal parts is also possible, such as adapting to different (less expensive) valve lifters, roller bearings in rocker arms that reduce internal friction power loss, and solid state ignition systems that actually work (NOT Pertronix!)

To the "numbers-correct" restorer with a library of dusty parts and service manuals that Fred Flintstone's mechanic once used, these modifications won't appeal to him at all. For the weekend cruiser or the guy who still does real truck stuff with his rig, the advantages should be worth the effort- - - - -a one-time "bite the bullet" expense to build an engine that ends up with more power, more accessible (and probably less expensive) rebuild parts- - - -all inside an engine that still looks "original" to the casual observer. That sounds like a "win-win" situation to me!
Jerry

One comment. When I modified my 216 to take a 235 crankshaft and rods, I needed to grind clearance flats on the camshaft, because the rods hit it every other revolution of the crank. Not a big deal, and maybe the half a tenth smaller BBC rods will clear even with larger stroke than a stock 235 crank. But rod to camshaft clearance is something to look out for.

Good point- - - -there's plenty of material between the lobes on a stovebolt cam to reduce the diameter a bit if necessary. Here's the rods I'm planning to use on the 216 I have in progress. The only modification it looks like they will need will be a smaller bushing to adapt to the Ford piston wrist pin. They're narrower than a stovebolt rod, but thrust washers around the wrist pin will keep the rods centered on the crankshaft journals.

www.ebay.com/itm/318726769217?

Here's an extremely high dollar- - - -high tech buildup of a 261 that incorporates a lot of the same ideas I'm using- - - - -and it demonstrates the durability of the stovebolt basic block and crankshaft design. "There's no substitute for cubic inches- - - - -and cubic dollars!" My build produces a bigger displacement, less exotic engine- - - -using mostly off the shelf parts, at a fraction of the cost!

www.trifive.com/threads/turbo-charged-261.250714/?utm_source=bing&utm_medium=organic

Jerry

Hold on -- To your point about the "Numbers Correct" restorer ... The numbers he (or she ) is concerned with are the casting numbers, date codes and serial number on the outside of the block. If we're doing all this on the *inside* of the block and thus unobservable unless one disassembles the engine to check everything on the inside (which, to my limited knowledge, is not a part of AACA judging ... ???), anything done on the inside would not alter the originality of the block itself -- it would still be "correct" to the truck, ja? It would still be Grandpa's original engine in Grandpa's original truck to the casual (and even the not so casual) observer? Perhaps an AACA or VCCA member (Tiny?) could offer a viewpoint here.

It seems to me that what you are talking about here is not only entirely doable and opens up a world of affordable driveability for the average restorer, but may even be an avenue open to all but the most fanatical of restorers.

To all of us with "original" trucks -- who wouldn't want to keep that original 216, but have it modernized and improved on the inside to enable modern driving pleasure?

It's brilliant, I say. Brilliant!

BTW- - - - -the same approach also works on MOPAR engines LOL!
Jerry

Haven’t read this all word for word, but I didn’t see anything mentioned about the better designed rear main seals Jerry has mentioned in the past. Nothing worse than having a great old truck but having to keep a drip pan or cardboard underneath.

If I was in the market for a rebuilt Stovebolt, I’d be way more interested in what Jerry is proposing than an original.

John

That rear seal modification will definitely be part of the upgrade. I'm in the "dreams and schemes" phase of planning a modification to the GMC 228-302 engines to use a modern 2-piece neoprene rear seal instead of the rope seal they were designed to use. That will require some machining to the back of the block and the rear main bearing cap to use a bolt-on 2 piece seal holder. I'm also in the process of designing a drill guide fixture to put pressure oiling passages in a 216 spray-oiler crankshaft.
Jerry

I think that will be a tough endeavor. Missing the big lightening holes in the crank pins will take some noodling. You may have to drill from both ends and make the holes meet in the middle.

I'm planning on installing a piece of heavy wall steel tubing across the hole, brazed or tack welded into place- - - - -probably a cut-off piece of small block Chevy pushrod.
Jerry