06-02-2021, 02:36 PM
Hi dannyteal
When I rebuilt my engine with new bearings (18 years ago) I was in ignorance about the niceties of paired bearings, preload etc. I just fitted off the shelf bearings from a cherished supplier, but the crank was MIGHTY stiff to turn due to excessive preload, i.e. the bearing balls being squashed into their tracks. I measured 1.5 lbs ft torque to turn the bare crank, the preload was probably about 10 thousandths of an inch, i.e. minus 10 thou of end float.
After some research and a steep learning curve, I took it all apart and fashioned a home made 7 thou spacer shim to go between the inner races. This reduced the preload to about 3 thou and the torque to about 0.5 lbs ft, which I felt was acceptable for a new engine.
I think part of the problem is that cherished suppliers have customers ranging all the way from those who do two engines a month to those who have never done one before. There is maybe a bit of an assumption that the need for fettling new parts is understood. For those used to modern cars where everything is close tolerance and fits straight away, it can come as a bit of a surprise !
When I rebuilt my engine with new bearings (18 years ago) I was in ignorance about the niceties of paired bearings, preload etc. I just fitted off the shelf bearings from a cherished supplier, but the crank was MIGHTY stiff to turn due to excessive preload, i.e. the bearing balls being squashed into their tracks. I measured 1.5 lbs ft torque to turn the bare crank, the preload was probably about 10 thousandths of an inch, i.e. minus 10 thou of end float.
After some research and a steep learning curve, I took it all apart and fashioned a home made 7 thou spacer shim to go between the inner races. This reduced the preload to about 3 thou and the torque to about 0.5 lbs ft, which I felt was acceptable for a new engine.
I think part of the problem is that cherished suppliers have customers ranging all the way from those who do two engines a month to those who have never done one before. There is maybe a bit of an assumption that the need for fettling new parts is understood. For those used to modern cars where everything is close tolerance and fits straight away, it can come as a bit of a surprise !