Post
by Wayne Sheldon » Mon Jun 26, 2023 6:30 pm
"Do I cut a 10-15 thou shim and see if I can get the bolt right and engine free, leave the bolt kinda tight but not tight or just leave it loose as it was and check it out after some driving?"
[/quote]
Clearly here, there are more immediate concerns, pretty well covered by others already. However, a couple things I would comment upon.
With tired abused and messed up old engines, anything more than just wasting some time to see how far you can make it go on minimum effort requires some degree of precision!
Whether poured Babbitt or insert bearings, the contact surface should be more than eighty percent of the total bearing surface, and about ninety-eight percent of the heavier stress areas in line with the cylinder. That much area must be within a one thousandths inch of perfection! Just a few high spots with a couple thousandths inch extra height may bind the bearing enough to keep the engine from turning enough to be started? Too much low area will cause the bearing to hammer out and crack, and eventually (and likely quickly!) fail totally.
Unless discussing the total amount of shim used? One never speaks of engine bearing shims in the "10-15thou" range. Final fitting of a model T's Babbitt bearings is almost always done with one final more or less "one thousandth inch" shim! Sometimes, and I have done this several times myself when I could get a few, the final fit is one more or less "one half thousandths" shim! Or, alternatively, a couple more "draws on the rod cap with a sharp very flat file.
Rod bolts should never ever be run loose! In truth, really early engines often did that by design. However, they were not intended to ever exceed about 300 rpm. The bolts being loose was how the bearing tightness was adjusted back in the early days. When rpm began to exceed about 500, it quickly became obvious that loose bolts on rod or main caps was NOT going to work for very long.
If rod cap bolts are not really tight, like nearly twenty foot-pounds tight, they WILL while running begin to shift about and work all connecting points in terrible ways. Flat surfaces, holes, bolts and nuts themselves, all will begin to be beaten and worn and become even more loose very quickly. Bolts WILL stretch! And then the Babbitt begins to hammer itself onto the journals.
Since I have almost always had to work with a tight budget, I have very rarely had an engine rebuilt by anyone else. Most of my model T (and even some newer vehicles?) engines I have reworked myself. Several of them I have gotten a lot of miles out of with no troubles after I reworked them.
For my model Ts, I find good looking used rods, mix and match styles and weights, then hand fit bluing and scraping the bearings. Then I use a balance scale that I made myself to balance the rods and pistons. Starting with an engine that isn't worn out, one can get a really great engine that way. If one makes the effort to properly fit everything.
