The Stovebolt Site Forums The Shop Area Engine Shop Update on my engine build.

I wound up going with 1950 Chrysler 250 CI pistons in 0.080 oversize (about 0.015 oversize of the 216 bore) with the 235 crankshaft and rods in my 216. I had a machine shop bore the block to fit the pistons and it cleaned up nicely, being standard bore. They also narrowed the #3 bearing journal to fit later 235 main bearings and bored the rear main journal area for a full circle seal. The also ground the 235 crank to 0.020 undersize.

I've gotten the main bearings fitted to the crank (took a few shims to get the clearance right), and today tried fitting a piston. The good news is that the piston crown sits about 0.020 proud of the deck, and the head gasket is 0.079 thick. Allowing for a little compression of the gasket, the pistons should clear the head without issue. The bad news is the skirt of the pistons is just a bit too long to clear the crank counterweights at the bottom of the stroke, so I'll hit up a friend with a lathe to trim the piston skirts down a touch so that the crank will go all the way around. I think I lucked out on which cylinder I picked as some of the cylinders have more clearance to the crank. It would have been bad to get them all in with rings, etc. and then find out the crank wouldn't turn. The 216 pistons have slipper style skirts, but the Chrysler pistons are full skirt like the 235 pistons are. I'll trim them to the same length as the 235 piston skirts to be sure they clear.

So the engine assembly is on hold for a bit until I get the pistons trimmed up.

What is the triangular cut in the piston top?

That's to indicate the front of the engine. Here's a cross-section from the 1955 2nd Truck Shop Manual that shows the notch.

I'm not an engine builder, but it looks like you have things under control. Man with a plan. Nice.

Machining .020" off the piston crown won't weaken it, if you choose to go with a zero deck height. The "front" notch is considerably deeper. The Japanese Diesel pistons I'll be using with a stroker crankshaft and 7" long GMC or flathead Ford V8 connecting rods have a crown around 1/2' thick, so the deck height can be adjusted with no danger of a piston crown blowout. Looking good so far- - - -I'm glad to see somebody thinking outside the box on these old engines! My bored and stroked "216" is going to end up around 258 cubic inches.
Jerry

Why a groove and mot just am arrow or something? Does it serve a purpose in operation?

Jerry, I don't think I'll bother trimming the top of the pistons. I'm pretty confident there won't be any interference.

Otto, No idea why that notch was selected. It's been that way for years. These pistons have an expansion cut on one side of the skirt (the one that gets less pressure - opposite the side that gets forced against the cylinder wall on the compression stroke.) Some pistons have offset pins for a similar reason. You'd have to ask the piston manufacturer for a real answer.

Pistons with a "front" indication- - - -notched, "F" cast into the wrist pin boss, or something else, almost always have an offset wrist pin. That allows the thrust face of the piston skirt to be firmly in contact with the cylinder wall before the spark plug fires. Put one in backwards, and there will be a very noticeable piston slap at idle.
Jerry

Make sure to check to see how much intake valve to piston clearance you have. I've heard of clay being used for this.

Kevin, looking GOOD! Just curious, have you considered cc'ing the heads and doing the math to calculate the new compression ratio? I suspect stock was in the mid 6 range (6.7). Always thought 8.0 or so would be nice, of course the bottom end would need to be up to snuff but you've taken care of that potential weak link.

RonR

ps, you do know that the addition of Mopar parts will be good for at least a 20% HP bump!

Looking good.

Remind me. Are you modding this engine to do pressurized rod oiling?

Very impressive. Definitely thinking outside the box.

Yes, plus a displacement bump with the 235 crankshaft. (230 cubic inches) I've got a couple of 216 conversions on the drawing board with increased bore and stroke, that gets a stock-appearing 216 up to 250+ cubic inches. A 235 with the same modified crankshaft and diesel pistons goes to 270 cubic inches and a 261 goes to almost 300.

A 216 with a 90.5 MM Mitsubishi K4N diesel piston and a 4 3/8" stroke 235 crankshaft goes to 261 cubic inches.

www.ebay.com/itm/164222309615?

That requires a LOT of creative metal butchering, though! Of course, beating your buddies pulling a long hill in high gear with a stock-appearing "216" is priceless!
Jerry

Yes, the impetus for this was that I burnt out the #1 rod last fall. Figured it was time to fix the babbit rod spray oiler issue once and for all. This should be a dependable engine once it's put together. This build is requiring a bit less "creative metal butchering" than Jerry's builds.
The one unusual snag was the piston skirts interfering with the crank counterbalances. Should be a relatively easy fix once I track down a lathe to use. One good friend has two of them, but neither is operational at the moment. Will be trying a different source. I could take them to the machine shop and pay for them to be cut down, but the friend route is better.

Cool. What was the idea in using the Mopar piston?

Jerry had suggested Buick 215 CI pistons. I looked at them but the piston crown was 1/8" below the deck and they have a dish in them, reducing the compression ratio quite a bit. Egge Machine came up with the 1950 Chrysler pistons. They had them in 0.080 oversize which turned out to be about 0.015 OS for the 3.5" standard bore of a 216, and the piston pins were slightly smaller than the 216-235 pins, so I sent them a set of pins and they fitted them to the pistons. That eliminated the need to bush the small ends of the connecting rods. Also, as mentioned the piston crown turned out barely proud of the block deck, so maximizes the compression ratio. Of course if the 216 block had already been bored, I'd have been out of luck, as the Chrysler pistons would have been too small even in 0.080 OS.

The Buick 215 pistons would require a longer rod to reach the top of the block, such as a GMC six (248, 270, etc). 85 HP flathead Ford V8 rods are also the same length, and a LOT lighter weight. The GMC rod runs the same size crankshaft journal OD as a Chevy stovebolt, but it's about 1/4" wider at the big end. It's 7" long. Milling the GMC big end width down to match the Chevy journal width gives a builder a better choice of pistons to use because of the longer rod length. BTW- - - - -I just bought (stole) a set of used 270 GMC rods and domed pistons from an Ebay seller who had no idea of their value, and I won't have a use for the pistons for any of my projects. They're available for horsetrades!
Jerry

Turning the skirts isn’t a hard job or a long one
Probably 2 hours.
Wouldn’t take much longer to shave .010 or .020 off the top.
Might want to weigh them when done

14 inch lathe with a good 3 jaw and a little self confidence and you’re good to go

I'm working on my friend to get his lathe put back together. It's pretty low on his list, unfortunately. I've offered to reassemble it for him when we can get together.

How much needs to be trimmed off the piston skirts? A disc sander and a pretty simple wooden holding jig would do the same job with a minimum of setup work.
Jerry

I haven't checked that closely, but the pistons that came out of the 235 should give me a dimension to shoot for (from the pin hole to the bottom of the piston.) The one piston I had installed just barely interfered. These pistons have a fairly heavy boss about 1/8" above the bottom of the skirt, so thinking trimming down to that point might do the trick. I may look into using an angle grinder. The suggestion to weigh the pistons to match them is a good one as well.

You could also do it on a mill I can think of at least 3 ways to do it on a mill.
Jig and a router would also work, your regular carbide wood bit will eat aluminum all day
Without taking any damage.
Make a box the piston will fit tightly in drill a cross hole to put your wrist pin in to hold the height,
So it doesn’t try and pull out of the box you get the Idea.
Think like a machinist if you have the tools at hand if not think like a furniture maker.

That will get the skirt cut down then just check the weight

My triple beam scale is accurate to +/- 1/10 gram. I weigh the entire reciprocating assembly- - - -piston, wrist pin, and rings, find the lightest one, and file, grind, or machine each of the other pistons to make them all match. A dollar bill weighs almost exactly one gram. I also have a ball bearing holding fixture to weight-match the ends of the connecting rods to the same tolerance, including the rod bearings, for big end weight matching. That's standard procedure on race engines.
Jerry

So while I was at the machine shop to talk about rebuilding my broken 7.3L, I mentioned needing to turn the bosses in the pistons down. He said, I can do that for $100, so I jumped on it. I picked them up yesterday and started installing rings, pistons and rods.
As my luck has been lately, I ran into another snag when the rods for #'s 3, 4 and 5 interfered with the camshaft. I checked the others and they clear by at least 12 thousandths. What I'm going to do about that is turn the camshaft down just a touch in the areas where the rods swing by. Rough (forged) measurement of the cam diameter is 1.2" so I'm thinking I can safely trim off 0.15". That's probably less impact on the balance of the rotating assemblies than grinding the spots off the rod caps. I'll run it out to the machine shop and see what he says. If it's another $100, I'll have him do that.

235 cam cores have flat areas between the lobes to account for the longer stroke, so that would be another option. Does the interference happen between the rod cap itself and the cam, or the bolt and nut assemblies? I'm planning to run the 261/Corvette cam in a 216 by turning the bearing journals down to 216 size. Those cams already have the long stroke relief built in. I'm putting 3/8-24 Helicoils in stovebolt rods, and using ARP style 12 point rod bolts that give the bolt approximately twice the thread engagement as a conventional rod bolt and nut. Obviously, I'll recondition all the rods after installing the super strong bolts to assure the bore is round and the right diameter.
Jerry

Jerry, the last one I checked (#4 I believe) only interfered with the cam every other revolution of the crank so the cam is presenting a little bit higher in that revolution (cam isn't completely round between the lobes - higher forging marks are evident.) Numbers 3 and 5 I think interfere every revolution as there's a band around the cam there that's higher than rest of the cam.
It's hard to see exactly whether it's the rod itself (not the cap as the rod is closer to the cam) or the bolt head (which is ground to help miss the cam) is hitting, but I believe it's the rod.

Grinding flats on the cam would be an option, but I'd need to reinstall the cam (already removed it) and mark where the clearance is needed, then remove it (again) to do the grinding. And not knowing just how much to grind off might make that a long process. I think it might be easier to just turn the cam surfaces between the lobes just a bit.

[on edit] Your idea of helicoils in the rods would get the bolt head on the cap end and out of the way of the camshaft.

Got hold of a 235 camshaft and ground matching flats on the 216 camshaft going in the engine. That didn't take nearly as long as waiting for the machine shop to turn the camshaft down for rod clearance. Got the camshaft reinstalled and the last two piston/rod assemblies and checked for clearance to the cam. All were good, so I can proceed with engine assembly. I need to order up valves for a valve job on the head, so that's the last thing that will go on.
Here's a couple pics of the clearance flats. They're not pretty, but the rods don't hit now.

Good on ya for being innovative! Since Melling is apparently back in production on their 261 clone cam (CCS-1) I'm planning to acquire some of those cams and modify the bearing journals to fit the 216 block. That should solve the rod clearance problem as well, since those cams are profiled for the 235 stroke already. I'm still in the R&D process for getting a 216 steel core cam ground for a roller lifter profile. I'll turn down the areas between the lobes with my lathe before sending the core off to have the roller lifter lobes ground. A thin sleeve pressed into the lifter bores on a stovebolt block will make mechanical roller lifters for a big block MOPAR engine fit.
Jerry

Sometimes builders machine the camshaft bore on a Cadillac V8 (425-472-500) a few mm and then use a Ford 429 cam blank. What would be the harm in machining the smaller 216 block bores out to the larger 235 size so it could take the stock larger cam and bearings?

Tronman, that would take more machine work, and the 235 cam I have is basically trashed. A little angle grinder work took care of it.

Jerry, FYI, cutting the cam down to 1" between the lobes will give you the clearance needed on the 261 cam.

The cam fits my lathe and I have a steady rest and a couple of tool post grinders- - - - -the block doesn't! I'd have to custom make a bunch of accessories for my line bore machine to enlarge the cam bores in the block. Also, I'm not sure the 216 has enough material in the block to do that.
Jerry

Ahh, that makes sense. I wasn't asking so much for this specific installation, just in general because it seems like the 235 cams are a lot more common. However at least they can be ground down and the lobes still fit through the holes.

Cadillac were kinda chintzy on the original cam diameter, so machining the holes a few mm larger could allow for more lift. Now you can get roller cams, so it doesn't matter as much. At least there's plenty of material in the Cadi block, so no worries there.

I'm also working on a roller cam core design- - - - -two pieces of steel shaft material, spliced together with a machined-down piece of a stovebolt cam with the distributor drive gear on it. They will be heated and shrink-fitted to the center piece, then tapered pins will reinforce the coupling. The two blank areas will be machined for the maximum possible lift on the lobe locations and left completely round, to give the cam grinder people as much raw material as possible to work with. The size of the third bearing journal will establish the max diameter possible for the core lobes. Since the cylinder head design prevents high RPM performance, I'll be going for rapid valve opening and maximum lift, to enhance the low and midrange torque capabilities.
Jerry

That sounds really cool! How come regular camshaft cores can't be ground as roller? (In other words, why do you have to make something like you plan to)?

Roller cams require a steel, not cast iron core. Schneider says a cast iron roller cam will fail in a matter of minutes after starting the engine. They've tried it! The only forged steel cam cores for stovebolt engines are for the 216 and early 235 engines, and they have the small diameter bearing journals. It would be possible to press sleeves over journals and machine/grind them to 235 size, but the roller lobe shape would be limited by the 216 lobe size. By making a completely round lobe the diameter of the #3 cam bearing, the cam grinder would have a much larger core lobe to work with. Comp Cams uses a similar procedure to grind cams for NASCAR engines, with a solid steel billet with a distributor drive gear machined onto one end. A few years ago when I got a tour of the Comp factory, that billet sold for $3500.00- - - -before grinding was done! Stovebolt cams present a problem, because the drive gear is in the middle of the cam, not on one end. Hence the necessity to use two billets, spliced onto a gear salvaged from a junk camshaft.
Jerry

Back on topic.

I cut the spray oil tubing and the dipper troughs out of the pan. They aren't needed with the full pressure oiling on the rods. See pic 1.
Today I tried fitting the oil pan on the engine and found it wasn't going all the way down. I first thought it was the oil pump pickup, but that didn't make sense, since everything there was the same as when the engine ran. The only thing that changed was the oil pump itself. I scratched my head a bit and finally discovered the one of the oil pan baffles was hitting the inlet fitting on the oil pump (circled area on pic 2.) I smeared a little gasket sealer that was handy on the baffle and put the pan in place and rocked it a little. Some of the gasket sealer transferred to the inlet fitting (arrow on pic 3.) So anyone fitting a M29 high capacity oil pump in a 216 will need to cut a little bit off the forward baffle. A little grinder work will take care of it by cutting a little crescent out of the baffle for clearannce.

"I love it when a plan comes together!" All these little tweaks are good to know- - - -you might want to consider detailing the process in a tech tip once the job is done. I've found another rod and piston combination that might work with the long stroke crankshaft- - - - -a 170 cubic inch Ford six has the right compression height with a stock stovebolt 235 rod, with the big end bushed down to use a Jeep CJ-2 or CJ-3 rod bearing. That will allow a 4 5/16" stroke and puts the piston very close to the top of the block.
Jerry

I got a notch cut in the oil plan baffle to clear the oil pump fitting and got the pan installed.