Just want to make sure I am doing this correctly:
To check bearing contact on the connecting rod, I pulled the cap and coated the bearing surface with a light coat of Prussian blue.
Re-assembled and gave it a full rotation.
Bearing is clean and shaft is now covered evenly with the dye.
Correct? Or is that too tight? Plastigage is showing 0.002"
The thinest possible coat will tell you if high spots are there.
Loose enough and "thick" coat conveys no useful info.
By high spots, see this machine part. A thick coat would just make a blue blotch and tell me hardly anything about where the high spots are.
a "Sharpie" marker will do the same thing for you and won't risk being too thick.
The problem with Bluing, is it is a to coarse of pattern.
The best way if you are scraping a bearing, is to tighten the bearing to a drag, and then remove it and scrape the spots that hit the crank, Not even oil on it.
If you are doing mains, never try to scrape a loose crank to the main bearings, as the crank under cap torque pressure, will show a different pattern.
Same thing as a cylinder torque plate when boring cylinders, they change under pressure.
Clearance on a Model T is .001 thousandths of an inch, so that would be .001-25 minimum, and plus 1/2 thousandths which would be .001-75.
.002 is to big.
I would take out a shim on both sides, oil it real well, and put it together.
The plastigage is not a useful measurement tool except when everything is of a known quality - new properly turned crank, new align bored bearings. Even then I prefer just measuring the parts and subtracting. Plastigage is a "pretty close" sort of / kind of way to measure things.
In this case you suspect you have a twisted rod. The plastigage can only tell you the dimension in one tiny spot, not in several spots, and it cannot tell you if something is bored true or not.
Dare I suggest Time Saver? Worked great for me on two T engines, one T tranny, and one hit and miss engine.
Yes Hal you gave the best suggestion for every engine O/H.