Jivermo wrote:
Now, other than a staggering amount of parts to clean, what next? Is this case salvageable, and what forensics path do I now embark upon to find out why this problem occurred?
Congratulations. You have arrived at the conundrum and been validated.
This is trickier than meets the eye. Bearing movement can cause imperceptible-but-critical wear of the saddle. When you look at the backsides of the bearings, they should not be shiny. You are fortunate that the case dowel hole is not wallowed out, but you now need to clean it very thoroughly (use a cold tank at a machine shop they will ding you for $20.00 +), then bolt up every main bearing bolt and peripheral bolt to proper torque, then get the bores measured by someone who can wield a top-drawer micrometer. We are measuring well within thousandths of an inch here.
My forensic guess here is that cheap too-small dowels were used, yes, but also the case was given a pass in the name of economy (thus the standard bearings) when it possibly needed to be bored to the next oversize. Remember, we have the actual case bore dictating the outside size of the bearings, and we have crankshaft journals dictating the inside size of the bearing. You can have std/std you can have .25/std, you can have .25/.25, you can have std/.25, now add to all of the prior derivations the .50 over/undersizes available, AND the undersizes for the thrust bearing where it is longitudinally indexed to the crankcase.
The best check of main bearing alignment is with a boring bar.
The bearings are supposed to be a press fit into the case, no wiggle. Remember that the case expands as it gets hot, so the bearings need to fit securely at room temperature. This is especially important for the thrust surfaces of the #1 main bearing, our problem child.
Bring your cleaned crankshaft (just wipe it down as dry as you can at home for politeness, no water) to the machinist-who-can-read-a-real-micrometer. You may need to have the crankshaft ground down at either/both the main journals and the connecting rod journals if they have gotten oval. After everything has been measured, you will have all the numbers you need to obtain the correct bearings. This includes the connecting rod bearings. Are yours also std?
Colin
(p.s. got the Tom Wilson book? It pretty much describes everything I flitted on about . . .
pay particular attention to the mm vs inch machine work vs metric bearing oversizes issues)
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles
