chaos.lrk.ar.us!dave.williams (Dave Williams)
hotrod  11 Jan 93
- I've been reading a pre-WWII book on auto mechanics, and it has a
  thorough discussion of how to pour and fit Babbitt bearings.  I'd always
  thought that, y'know, you just flipped the engine over, took off the
  pan, and poured it in somehow.  Nope.  First you get to chisel the old
  Babbitt out, then you clean endlessly because any water or oil will make
  the new metal bubble, then you clamp this wierd fixture across the main
  web and put in a plug approximating the crank journal diameter (and
  they're all different, do the thing is a "universal" fixture which
  probably worked about as well as you'd imagine).  Then you heated the
  Babbitt in your furnace and poured at red heat.  After it cooled, you
  cracked the pouring fixture pieces loose and had this big wad of metal
  (hopefully) stuck to the block, with fins, flashing, and drools of
  escaped metal run down into the rest of the motor.  You got to spend a
  while trimming off the excess, and then you got to repeat the entire
  process for the rest of the bearings AND their main caps.
- Assuming you got through all that without Babbitting your foot or
  setting anything afire, you got to fit the bearings.  In a large shop
  you'd have a line boring machine available, much like large shops do
  today.  A smaller shop might use a reaming stand and fixture.  If you
  were in a small town, ye olde mechanic probably had to scrape the
  bearings to fit.  This meant using metal scrapers, which were shaped
  more or less like scalpels or midget fancy butter knifes, and carving
  the soft Babbitt metal to a reasonable fit to the crank.  Once the crank
  would actually go in, he'd use Prussian blue to find the high spots,
  scrape, blue, scrape, etc.  Of course, scraping too much would require
  starting over again, so he'd be very careful.  Oh, yeah, he also got to
  cut the oil grooves by hand, too, to the pattern required by the auto
  manufacturer.  Not cutting the grooves would be a bad idea, since most
  Babbitt bearing engines used dippers and splash lubrication rather than
  pressure oiling.
- Once he had about a 75% fit between the crank and bearings, he'd clean
  everything off, bolt the crank in, and (if he was a perfectionist) would
  lap the crank in by running it with an electric motor.  Then it all came
  apart again so the rest of the engine could be assembled.  All in all,
  it sounds like a full day's work, and one requiring a fair amount of
  specialized machinery (and that's even assuming the crank didn't need to
  be turned due to flat spots or taper wear, which the book assures us
  happened often).
- Nowadays we simply wipe everything out with a paper towel, pop in new
  bearing shells, mike the crank to make sure it's round, and use a piece
  of Plastigage to make sure the bearing manufacturer didn't have a QC
  problem.  Voila!
- Ah, the good old days...

[email protected] (Dave Williams)
fordnatics  03 Jul 1997
- -> Could you please explain to me exactly what a babbit bearing is?
- Babbitt metal is a low-melting-point bearing alloy.  It was developed long 
  ago, predating the automobile, by a guy named Babbitt.  There are several 
  types of babbitt metal, originally with a numeric designation, though the 
  SAE babbitt designations are used now.  Babbitt metal is still used today in 
  many insert-type automobile bearings. 
- When someone refers to "babbitt" in general, they're usually referring to 
  the old style "babbitted" main and rod bearings.  Chevrolet was the last US 
  auto manufacturer to abandon babbitted bearings.  Even the flathead Fords 
  had gone to inserts by then. 
- Take a block, flip it upside down, and drop a crank into the bare block.  
  Bolt on the main caps.  Use some special fixtures to hold it up off the 
  block, more or less centered in the main bores.  Dig through a *big* box of 
  special fixtures to add side plates to each bearing journal.  Now drop your 
  block of babbitt into the melting pot - looked a lot like a reloader's lead 
  pot - and melt it.  Take your dipper and pour the hot metal into the holes 
  on the main caps.  It'll run out all over the place.  The stuff cools pretty 
  quick, so you unbolt the main caps, cut them loose from the still-soft 
  metal, and pull all the side plates and the crank.  Take your knife and a 
  chisel and remove all the metal that ran out of the bearings.  Now you take 
  your three-cornered scraper and shave the newly cast babbitt to establish a 
  running clearance between the crank and the new bearings.  You will have to 
  lift the crank back in and turn it every now than then; it'll leave marks to 
  show you how you are doing.  Then you might carve a deep "X" or other 
  pattern into your new bearings of the spec book calls for it; lots of the 
  splash oiled engines did that. 
- Fancy shops had line-boring equipment and saved the scraping step. 
- Then, once the mains were done, you got to do all the rods.  Some rods had 
  stacks of shims between the cap and fork.  You added enough shims to bring 
  it back up to spec before casting the bearings.  Every 10 or 15 thousand 
  miles a service station would drop the pan, unbolt the caps, and remove a 
  shim or two to tighten up the bearings.  This used to be part of a tune-up. 
- Nowadays you open the box of bearings, pop them in, mike them to make sure 
  they're the right size, and you're done.  I don't know of anyone who longs 
  for the good old days of babbitt bearings... 

[email protected] (Dave Williams)
diy_efi  02 May 1999
- -> Please explain the term "floating rod bearings"......... I've
  -> never heard it before...... The only "floating rod bearings" I've
  -> experienced are those which spin between the bearing and the
  -> rod.......... Definitely a bad deal.... forshadows doom!
- Back in the 1930s many engines used bearings that were cast directly onto 
  the rod or block surfaces and machined or scraped to size.  The bearing 
  material was an alloy called Babbitt, (there were actually a number of 
  different Babbitt alloys) and the resulting bearings were referred to as 
  "babbitt bearings." 
- Cast babbitt bearings were relatively time-consuming to make, so as labor 
  prices went up they became less cost-effective.  It was also found that 
  thinner bearings could hold up to load better than thick bearings. Many 
  engines began using "shell" or "insert" bearings - thin strips of steel with 
  a thin layer of bearing material - Babbitt alloy, lead/silver, etc. - cast 
  or laminated in place.  These bearings were normally a tight fit in their 
  housings; in fact, the OD of the bearing was usually slightly *larger* than 
  the housing; the difference is called "crush" and is what keeps the bearing 
  from spinning in the housing. These types of bearings are in common use 
  today. 
- Ford went to an insert bearing on the flathead, but the rod bearings were 
  strange - they were babbitted on both sides, and floated in between the 
  crankshaft and rod.  Later they went to conventional interference fit 
  bearings.  The hot-rodders of the day claimed there was little difference 
  between the floating and interference bearings.  I've found no detailed 
  technical information on why Ford chose to do the floating bearings instead 
  of interference bearings, or why they changed.  I suspect it had something 
  to do with cost, as the flathead V8 was rigorously designed down to a price.