Model A & B

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Tin-based Babbitt Bearing Grades

Grades & Numbering Conventions

Babbitt can be characterized as either Tin-based or Lead-based.

Originally Ford Motor Company used tin-based bearing metal (babbitt) made to their own specifications and requirements by the National Lead Company, and paid no apparent regard to what babbitts other manufacturers in industry were using, or how others were naming and specifying it.

In subsequent years the automotive industry primarily used the SAE J460 specification and numbering system to describe the composition and requirements of different babbitt grades commonly used in automotive applications.

In the 1980's and 1990's the automotive OEMs also used ISO specification and numbering systems to describe the composition and requirements of different babbitt grades used in automotive components.

UNS numbering systems were also sometimes used to describe the composition and requirements of different babbitt grades.

Today ASTM B23 grade specifications are typically used in a broad range of US industry to describe the composition and requirements of different babbitt materials and grades.


Lead-Based Babbitt

Lead-based babbitt metals were never recommended for use as engine main bearings under impact or cyclical loading, though they were used in some instances in automotive camshaft and transmission bearings (bushings) where the forces acting on the bearing were more uniform and without impact or reversal.

Lead-based babbitt won't last long as an automotive crankshaft main or rod bearing. Lead-based babbitt is not discussed further here on Ford Garage.


Tin-Based Babbitt Comparisons

The following chart is a comparison of various specifications of tin-based babbitt bearing grades used for automotive poured bearings such as found on Model A Ford engine crankshaft main and rod bearings.

Chemical compositions of babbitt are expressed in elemental percentages, either as a range, or as a maximum value. Many specifications have been created and obsoleted in the last 75 years, but listed below are the common ones from the last 30 years or so for tin-based babbitt grades.

Sn is tin, Sb is antimony, and Cu is copper. These are the three principle components of tin-based babbitt. All other elements are trace elements in varying maximum allowable levels.

Tin is what actually does all the work of providing the lubricity and the bearing surface.

Antimony is added to the matrix for hardness and to control the shrinkage of the hot poured bearing as it cools.

Copper is added to the matrix to impart both strength and malleability to the bearing to resist fracture.

Other trace elements are allowed but not necessarily desired in automotive engine bearing babbitt.
Pb is lead, As is arsenic, Fe is iron, Bi is bismuth, Cd is cadmium, Zn is zinc, and Al is aluminum.

Babbitt
Specification
Sn Sb Cu Pb As Fe Bi Cd Zn Al
Ford (National Lead) 86.0 7.0 7.0 0.50 0.10 0.08 0.08 0.05 0.005 0.005
ASTM B23 Grade 11
UNS L13870
(SAE J460 Grade 11)
86.0-89.0 6.0-7.5 5.0-6.5
ASTM B23 Grade 3
UNS L13840
83.0-85.0 7.5-8.5 7.5-8.5 0.35
ASTM B23 Grade 2
UNS L13890
88.0-90.0 7.0-8.0 3.0-4.0
ISO SnSb8Cu4
GM4031M
SAE J460 Grade 12
0.10 ~
SAE J460 Grade 17 85.5-88.5 7.5-9.0 0.50 1.0-1.5

In the table above, the various specifications are listed approximately in the order of closest match to the original Ford Babbitt composition produced by the National Lead (and tin) Company.

ASTM B23 Grade 11 babbitt is presently the most readily available match to the original Ford engine bearing babbitt. ASTM B23 Grade 2 babbitt would be the next closest choice after Grade 11. ASTM B23 Grade 3 babbitt is also commonly used by many rebuilders for Model A and B Ford engines.

A variety of nicknames and trade names have been applied to various babbitt compositions over the years such as "High Speed Nickel", "XXXX Nickel", "Government Genuine", "Imperial", "Nickel Genuine", "Diesel Babbitt", and others. It is all branding and marketing! The names sound nice but actually don't mean very much. You really need to know the chemical composition from the smelter that produces it or the industry specifications that it meets. BTW, no babbitt metal contains any amount of elemental nickel!


Final Thoughts

Knowing and choosing the right bearing metal is just the beginning. Now you have to find the guy that has the right know-how, the right equipment, and most importantly, the right attitude to pour it at the correct temperatures and according to the bearing metal manufacturer's instructions.

If your rebuilder can't tell you what grade and composition of babbitt he is using, or what temperature he is pouring at, it is time to find another rebuilder! The same is true if you find out he is using lead-based babbitt rather than tin-based babbitt for crankshaft main and rod bearings.

By-guess and by-golly is great for do-it-yourselfers who don't mind doing it over and over again, but a real professional knows the right materials and how to properly use them.


More related information on Ford Garage:

  1. Model A & B Babbitt Bearings and the Effect of Shims
  2. Model A & B AER Insert Main Bearing Data & Instructions
  3. Model A Bronze Rear Main Bearing Thrust

February 2001