The Stovebolt Site Forums The Shop Area Engine Shop Saving a "worn out" 216 crankshaft

Here's another one of my off-the-wall ideas- - - -most people think that once a crankshaft gets reground to .030" undersize or so, it's junk. "T'aint necessarily so!" How about finding a smaller-diameter bearing to adapt to the undersized crankshaft? I've been kicking around the idea of adapting Babbit bearing 216/235 rods to a more available, less expensive bearing than the one that's being used now, and I believe this idea would also useful for salvaging some crankshafts that might be discarded otherwise.

A Federal-Mogul 2015 CPA rod bearing that fits several Massey-Ferguson tractor engines can be fitted to a bored-out 216/235 Babbit rod, and actually requires slightly less material to be removed from the rod than the regular insert conversion requires. Here's "the rest of the story" as Paul Harvey used to say- - - - -The M-F rod journal is approximately 1/16" smaller diameter than the Stovebolt crankshaft, so those "trash" crankshafts that have been scrapped before can now be reground to -.060" and run a standard-diameter Massey-Ferguson rod bearing! 600+ HP NASCAR Chevy V8's run Honda rod bearings that are much smaller diameter than Chevy OEM bearings and stay together, so why wouldn't a low-speed, low torque stovebolt six be able to do the same thing? As soon as I get my rod reboring equipment up and running, I just might offer somebody a resized crankshaft/rod setup as a test bed.
Jerry

Sounds very interesting.......

A bearing set for a 3-cylinder M-F engine is $15.00 on Ebay- - - -that would be 30 bucks for a set of 6! How does that compare to the conversion bearings Egge Machine sells?
Jerry

The only thing I have heard about cranks getting ground is the thickness of the hardening on the top surface. It may all be rumors, but after .030" the crank surface can become softer if the hardening didn't penetrate. Again, thats what I have for years. But I agree with saving older parts, and a low hp engine surely wouldn't hurt a crank with the limited use they get.

I think its definitely worth looking into. I'm not sure there is a down side unless maybe the -0.060 grind is starting to get into some metallurgic property that is undesirable on the crank. Even then, it will probably still last nearly as long as a normal rebuild would. I suppose the other issue would be needing rods that haven't been converted to the usual inserts, if you already have them and are needing a rebuild.

I seriously doubt that a stovebolt crank got much, if any surface hardening, even when brand new and standard diameter. Getting a surface hardening job to penetrate more than a few thousandths would be quite a chore. Even the race cranks we paid big bucks to get nitrided only got hardened about .005" deep or so.
Jerry

Way back in dinosaur times when I was a kid and WWII was happening parts and tires were non existent so shops would grind a crank till it was round and then pour Babbit till the hole in the rod could made to be the same size as the crank. The engines were very low compression/rpm and the roads of that time set an automatic low speed limit. Don't know why a smaller crank pin and bearing would be a problem. The smaller the journal the slower the surface speed and less heat from friction. I'd give one a try in an instant. Would be interesting to set a crank in V-blocks and have a hydraulic ram with a pressure gauge read out to see at what point of under size journals the crank becomes more flexible.

Well Jerry, I figured you would start climbing the walls in a few days after your hand surgery, and I think I am right. I don't know enough about machining to even try to sounds intelligent, but the idea of mixing/matching/machining obsolete parts is a very creative idea and a great way to repurpose good parts. I would love to see you "test" the idea.

The advantage of a steel-backed bearing over simply increasing the thickness of the Babbit should be that the soft bearing material is at a minimum. That, plus the slower surface speed of the smaller diameter journal should allow the modified engine to live at somewhat higher RPM. Add a set of lightweight aluminum pistons, and the old babbit-pounders ought to be able to keep up with traffic for a change! Add the high volume oil pump conversion I'm working on, and things could really get interesting!
Jerry

Go for it Jerry. I like "interesting" things. Thinking out of the box is where a lot of the great things we have today came from......easy does it on the wrist though. (Telling that to Jerry is like talking to a wall.....they don't hear a thing)

Jerry, good luck! The one good thing about my 261 project being stalled as I wait for parts is that maybe your high volume oil pump will be ready before I button up the bottom end!

Matt