Quote:
Originally Posted by 1930artdeco
But, if burnishing the main bearings is more accurate than line boring I am surprised nobody has come up with an interesting way to recreate a burnishing machine. I am assuming it can be done with modern parts in a shop. Whether it is cost effective for a small time shop I don't know, but for a bigger shop?
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Just so we are clear Mike, the bearings still must be line-bored as a way to ensure all three are coplanar. What the burnishing is doing is making the surface area of the bearing be closer in the dimension and shape of the crankshaft's journal.
Alternately to burnishing, the bearing clearances can be taken up by removing shims after running the engine '
XX' (-i.e.: small) amount of miles. The definition of '
XX' is different depending on the quality of the line-boring job and/or the Babbitt material composition. After operating the engine for the '
XX' period of time, the bearing clearances can be adjusted because the wear during that period has provided more contact area of the bearing against the journal pin. The time between the next adjustment period will/should be longer since there is now more bearing surface contact area to support the crankshaft.
There are still custom engine rebuilders that do still burnish bearings. Some do have specially-made machines that do the burnishing. I know of three or four creations that work very well.
Remember, the downside to this procedure is that it takes additional time. Time is money for most shops (-and most Model-A customers tend to be frugal
). The upside to doing this procedure is the bearing is denser and the contact area is much greater which adds longevity. It is very feasible for the first bearing clearance adjustment to be done at the 20k-25k mileage mark. Because of the babbitt density and thickness, with prudent driving habits (-no detonation, proper oil change intervals, etc.) a babbitted engine can outlast an inserted bearing twice-fold.