What is Babbitt?
The babbitt that we use in Model T and A bearings (along with a host of other antique engines; both gas and steam) is a type of “white metal” bearing material known in industry as “tin-based” babbitt. (as differing from the sometimes softer lead-based babbitt; of which more later) According to records, the Ford factory used a babbitt of approximately eighty five percent tin, seven percent copper, and seven percent antimony; the balance assumed to be impurities and various alloying agents. At the time, that type of babbitt was simply referred to a “hard pein babbitt”; the term referencing the tensile strength (compared to lead babbitt) of the material and the usual method of post-pour swaging or peining that was employed to seat the babbitt in the journal box.
Ford accomplished this peining process after boring and semi-fitting/finishing the bearing by scraping (of which little was done) the crankshaft was clamped tightly in the new bearings and the bearings were “burned in.” More precisely they were “BURNished in.” This burning in process involved the crankshaft being so tight in the bearings that when revolved by a thirty-horsepower machine with the bearings were liberally oiled; the oil was supposed to smoke, or the bearing was considered to be too loose and shims were pulled and the whole process started over until the oil smoked!
There have been endless discussions and much derision of this process. K.R. Wilson was highly critical of it, though not, as we shall see, because it didn’t work but rather because it was at variance with what he sold. As a mass production method, for this type of bearing, is was an ingenious system!
My Crankshaft Grows?
The Ford crankshaft when subjected to the temperature at which the oil would smoke would have expanded in diameter about one and one half thousands of an inch. (.0015) a number never to be forgotten as it is the ideal clearance diameter for a journal of one and one quarter inch (1.250”) diameter; the size of the Ford crankshaft. So that, when the crank was revolved and the friction thus created raised the temperature of the crankshaft to the point that the oil would smoke, a temperature well below the melting point of the babbitt; the babbitt did not burn (albeit the oil made it seem so to the non-engineering eye of the workers) but was in fact rolled out (by the crankshaft journal) to the precise diameter of proper clearance for that individual journal on that particular crankshaft. This eliminated the necessity for individual boring and fitting of bearings to the inevitable variables in dimensional tolerance which must accompany mass production! It was simple and it was genius!
Other manufacturer had tried this method, but no one else was manufacturing engines on this scale. Many manufacturers such as Cadillac and Packard used the align-reaming method for final fitting and alignment as it was a simple way to control diametral tolerance whilst maintaining perfect alignment of the crankshaft through the main bearings. If you’ve ever tried to bore several separate bearings so that a shaft running through them will be in perfect alignment and turn effortlessly without binding; you may appreciate the complexity of the problem. Euclid tells us that a straight line is the shortest distance between two points; not three! Whilst the burning in method has the slight advantage of the “peining to size” property; the align-ream process has the advantage of not twisting the crankshaft in the initially tight bearings until heat achieves its purpose in clearance.
At KMW I achieve both by align-reaming and roller burnishing. The other advantage of the burn in process is that it was done without the rods or pistons being present. The same heat that expands the crank journal (co-efficient of expansion) also causes the crankshaft to grow in length approximately one tenth (.100”) of an inch. That is a lot of movement. This is an especially deleterious situation because of the location of the thrust surfaces of the Model T engine.
Because these thrust surfaces are located on the third main rather that on the centre main as in most engines; the crankshaft can only grow in one direction as it is trapped in the third main. This tenth inch growth occurs at approximately five hundred degrees fahrenheit and is all directed toward the front of the engine. If the rods and piston were on the engine when this movement took place, it would cock the rods, (especially the number one rod due to its foremost position,) and pistons in the cylinders and score the cylinders and pistons and possibly bend the rods.
The Ford engineers eliminated the possibility of this happening through the artifice of the “burning in” method. In spite of their efforts it was an all too common occurrence to see Model T engines with number one cylinder “pumping oil”. This, however, was due to operator error allowing the engine to overheat by not observing the required “break-in” period for the new engine.
Other manufacturer had tried this method, but no one else was manufacturing engines on this scale. Many manufacturers such as Cadillac and Packard used the align-reaming method for final fitting and alignment as it was a simple way to control diametral tolerance whilst maintaining perfect alignment of the crankshaft through the main bearings. If you’ve ever tried to bore several separate bearings so that a shaft running through them will be in perfect alignment and turn effortlessly without binding; you may appreciate the complexity of the problem. Euclid tells us that a straight line is the shortest distance between two points; not three! Whilst the burning in method has the slight advantage of the “peining to size” property; the align-ream process has the advantage of not twisting the crankshaft in the initially tight bearings until heat achieves its purpose in clearance.
At KMW I achieve both by align-reaming and roller burnishing. The other advantage of the burn in process is that it was done without the rods or pistons being present. The same heat that expands the crank journal (co-efficient of expansion) also causes the crankshaft to grow in length approximately one tenth (.100”) of an inch. That is a lot of movement. This is an especially deleterious situation because of the location of the thrust surfaces of the Model T engine.
Because these thrust surfaces are located on the third main rather that on the centre main as in most engines; the crankshaft can only grow in one direction as it is trapped in the third main. This tenth inch growth occurs at approximately five hundred degrees fahrenheit and is all directed toward the front of the engine. If the rods and piston were on the engine when this movement took place, it would cock the rods, (especially the number one rod due to its foremost position,) and pistons in the cylinders and score the cylinders and pistons and possibly bend the rods.
The Ford engineers eliminated the possibility of this happening through the artifice of the “burning in” method. In spite of their efforts it was an all too common occurrence to see Model T engines with number one cylinder “pumping oil”. This, however, was due to operator error allowing the engine to overheat by not observing the required “break-in” period for the new engine.
Model T and A Engines Need a Break-In Period?
Most commonly the engine was overheated shortly after purchase by the failure of the owner to comply with the break-in restrictions posted on every car at the time of delivery. The break-in requirement was that the car was not to be driven over twenty miles per hour for the first three hundred miles. This was not to break-in the main bearings; that had been done at the factory. However, the rings did need to seat in the cylinders. If the engine were run too fast before this was done the excessive friction between the rings and cylinders would produce considerable heat. This heat would then be carried by the hot oil running from the cylinder walls down onto the crank shaft. The crank shaft would then expand as it did in the burning-in machine, only this time the rods and piston were present. Number one piston would be cocked in the cylinder when the crankshaft expanded one tenth of an inch and would then wear the cylinder elliptical. The rod would also be bent and so all future attempts at fixing the oil-pumping number one cylinder would be fatally flawed unless the cylinder was rebored, the rod replaced, and new piston and rings fitted.
Of course you do not rebore just one cylinder as they must all be the same size; so a near complete rebuild was the only solution which, of course, few owners were willing to do. So, it smoked! until some non-engineering type got the bright idea of drilling holes in the bottom of the oil-ring groove in the number one piston. The idea behind this being that if we cut down on the amount of oil being put on the cylinder wall, then the engine will burn less oil. And so it did, for a while. The oil groove and ring were designed to distribute oil to the cylinder walls thus reducing the friction between the piston and cylinder. What these holes did was drain the oil from the oil groove. Without oil there was greater friction, more heat, and finally the further wearing of the cylinder walls; soon the engine was pumping oil and smoking again! There are no Shortcuts! Even an engine that has it’s bearings done by the align-reamed process (as I do) must have a break-in period until the rings “seat in.” I have seen at least one newly rebuilt engine; from which we removed at least one cubic in. of cast iron filings, all of which came from the cylinder walls, completely ruined through the failure of the operator to properly break-in (keep it cool and lightly loaded) the engine. More on this on a later web page. Suffice it to say that break-in is critical to the life and longevity of the Model T engine.
Contact: 775-883-3324, [email protected]
Of course you do not rebore just one cylinder as they must all be the same size; so a near complete rebuild was the only solution which, of course, few owners were willing to do. So, it smoked! until some non-engineering type got the bright idea of drilling holes in the bottom of the oil-ring groove in the number one piston. The idea behind this being that if we cut down on the amount of oil being put on the cylinder wall, then the engine will burn less oil. And so it did, for a while. The oil groove and ring were designed to distribute oil to the cylinder walls thus reducing the friction between the piston and cylinder. What these holes did was drain the oil from the oil groove. Without oil there was greater friction, more heat, and finally the further wearing of the cylinder walls; soon the engine was pumping oil and smoking again! There are no Shortcuts! Even an engine that has it’s bearings done by the align-reamed process (as I do) must have a break-in period until the rings “seat in.” I have seen at least one newly rebuilt engine; from which we removed at least one cubic in. of cast iron filings, all of which came from the cylinder walls, completely ruined through the failure of the operator to properly break-in (keep it cool and lightly loaded) the engine. More on this on a later web page. Suffice it to say that break-in is critical to the life and longevity of the Model T engine.
Contact: 775-883-3324, [email protected]
