I'm sure I knew about this odd bearing set up many years ago. But never having the chance to actually work on one of these engines, this little fragment of knowledge got pushed aside and replaced with piles of equally useless information. However, some recent research into something completely unrelated refreshed my memory of this unusual bearing arrangement. And then that lead to visualizing how two connecting rods can run on a common pair of double-width bearing shells. But then things got a little murky again. I know how the crank pin is machined and finished into a smooth, load bearing surface. But how does the I.D. of the big end of the connecting rod get finished to the same type of surface?
I had one in 1960, I believe if my memory is right 29A rods on a Merc crank, Michigan silver cadmium bearings= full floating. I had a L block, 50 Merc crank, bored on eighth = 276 CID
Just like polishing the Crank surface. The Rod is honed just as any other rod then a much lighter compound stone for final sizing.
This post is more of a question than it is adding info to the thread. In 1960 I was 16 and got a short lived summer job as both a gas jockey and apprentice mechanic. One job I was assigned was to pull the flattie V8 from a late ‘30s or early ‘40s ton and a half truck. Then, disassemble it for the shop owner to overhaul. From prior limited experience I knew the general characteristics of common engines. What I dimly recall discovering when I pulled the pistons and rods was the very style of rod bearings mentioned above. Single double width rod bearings that were free floating on the crank journal and inside the rod big ends as described in @ClayMart post. I had never seen that before, nor since in a flattie V8. I do recall the truck was just an aging farm truck and otherwise absolutely ordinary. Am I having a ‘false memory’ experience or where some/all flatties so equipped in the era that truck was produced? Ray
Flathead Fords used floating rod bearings from late '36 up through '47 truck/'48 cars when they went to modern insert bearings with the 8BA engines.
I was looking at bearings for a build lately. I think i have this right, the floating bearings for 59AB motors are like $420, the insert bearings were $140. It seems we found uses for all our leftover 8ba cranks and rods, folks should throw one of those in and save almost $300 on bearings. Same for new cams, those seem to have gone up in price again, saved money getting a good cam reground.
Some of you Kids crack me up. Prices have nothing to do with Cost to make or do no matter the item. Life is just a Numbers game. You tell me I have to pay my workers more per hour, I have to raise the cost of what we make. I sure as Hell am not going to dig that extra raise money out of my own Wallet. Nothing changes except the Numbers.
The 59AB engine in my '47 Ford had full-floating bearings. I was driving it one day and engine started knocking. So I limped it home. Drained oil, lots of bearing pieces came out in the oil. Uh oh. Pulled engine. Rod bearings had delaminated. Machine shop said it was because aftermarket bearings that were in the engine were junk. They found some quality ones. They also told me the rods and crank were not damaged at all and I was good to go with new bearings. New bearings, put engine back together, ran great.
Those floating bearings were almost in destructible if set up correctly. Setting up clearances was a pain in the ass in my opinion, though. They ran pretty loose ( .004 - .005 combined) compared to the precision inserts. They came in under size to fit the crank and oversize to fit the rods. Now they are hard to find in any size and expensive. If the engine is a 59AB with 3 1/16" original bore size the 8BA crank and rods will fit right in. You do need to use the earlier main bearings, though. The width of the tang on the bearing shell is wider than the 8BA. To use an 8CM Mercury crank and rods requires an over size bore to keep the rods from hitting the cylinder at TDC. You can use an 8BA cam but you have to use the matching timing gears with it. The thrust is different between the two.
I think I recall an article or maybe a question in a tech column in an old magazine about converting the SBC to full floating rod bearings. My take now is that was more about the good reputation of the full floating set up than any deficiency in the original SBC oiling system or bearings.
@Dan Timberlake I seem to recall a similar article in one of the old magazines but it was done to one of the early hemis.
The full floating bearing surface contacted each side at half the speed. I’d guess that is why racers in the 50’s installed them in engines they didn’t originally come in (info from Bruce Lancaster years ago).
The idea of honing the rod ends to size makes perfect sense, like reconditioning connecting rods on a more conventional later model engine. Though when I think of honing I tend to think more of a cross-hatch finish like in a cylinder bore. Fine for seating piston rings but not ideal for running against a bearing shell. But with a fine enough stone run with the right tension and at the correct speed I imagine you could end up with a finish like what you'd see on the crank journals. Nothing I've found online so far though really shows the finish on the I.D. of the rods, or even says much about it.
There was a special machine made for honing the Ford rod big ends. It did a great job and the rods looked like new. The machines were probably only available to Ford dealers and authorized rebuilders. Over size bearings were available in several sizes. I have a nice set of rods for a 221 cu. in. engine that are .008" over size. That was one of the standard offerings when the bearings could be purchased.
It has to. If you leave a course cut of hash marks it will be like a file against the bearing surface and you'll soon be back inside the motor again.
Well surprise, surprise! Our friend @Mart from Mart's Garage also gives us a demonstration of working with Ford's floating bearings. Mart also approaches it mainly as a "touchy-feely" procedure. But then this ain't exactly "rocket surgery" here, is it? If you want to go directly to the floating rod bearing stuff, skip ahead to about the 18 minute mark.
Some floater history and info about the stroker cranks The full floating bearings in Ford flatheads began in 1932 with the first production flathead V-8. The Ford flathead connecting rod bearing surface was nicely ground like the crank journal. The early flathead V-8 crankshaft rod journal was 2 inch diameter with a stroke of 3-3/4 inches the 2 inch rod journal size continued into the early 40's. When the Mercury 4 inch stroke crankshaft came out in 1949 the rod journal diameter was larger. Racers quickly figured out if the Merc crank was off set ground down to the 2 inch journal size the stroke was increased by 1/8 of an inch thus making a 4 -1/8 stroker crankshaft. Now those early floater connecting rods and bearings could be used on the now stroked Merc cranks using regular Ford parts. The best of those early connecting rods was the 21 A rod. The holy grail engine combination in many Hotrods and race cars in the day included the 4 -1/8 stroked Merc crank and a set of 21a floater rods. Heck even today the set up is still sought after. Ronnieroadster
Well, cut off my legs and call me Shorty! I had no idea the early flatties were built like this. I didn't think I was going to learn anything today. Then BOOM, I learned about full floating bearings. Goodnight.
I know! Wouldn't that like to dunk your hat in the crick? The more info I find on them, they also seemed to see some usage in aviation and motorcycle engines. Probably more so in the past than present.
This is what I have in my '40 Tudor. 4 1/8" stroke and .125 over bore. Comes out around 286 cubes. 8ba block with '48 and earlier type Offy heads and Offy 4bbl intake w/ WCFB carb. Early Mallory dual point 8ba type distributor. Runs strong, tons of torque. Dave
I was thinking main bearings in late '37, that went from babbbit to insert. My bad! Thanks for the correction Ron.
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