I plastiguaged the mains and found the front 4 showing approx .0020” while the back 3 are showing close to .0030”.
I then purchased a budget 2-3” micrometer and a dial bore gauge to make measurements.
Running the scat/eagle 4.2l crank.
I have standard sets of both King and Mahle Clevite bearings.
The kings measure up at about .0035” clearance and the mahles about .003”.
Strange the plastigauge shows approx .001” dif. between front 4 journals to back 3, but when measuring I cant pick up much of any difference.
Service manual calls for .0010-.0025”.
Hearing engine builders will use the .001” for every 1” of crank journal diameter rule of thumb, our cranks are 2.5” so that gives us a .0025” target.
Summit does carry Crown .002” undersized bearings for the 87-90 blocks, (J8133682 mains) (J8133683 thrust)
.002” undersize would put me at .0010-.0015” theoretically, which is probably too tight.
Haven't been able to source .001” under bearings
I could grab .010” undersize Mahles and have the crank ground to match.
Maybe a shop would be able to polish a crank down by .001” to make the .002” under bearings work?
Or I just run it with the mahles and hope my ~.003” clearance is okay. (~.0005” over the max spec)
How much bearing clearance would you tolerate?
Seeking any advice, bearings aren't cheap either so trial and error is pricey.
Am I making a bigger deal out of these numbers than I should?
What would you do?
Photos attached to help show what Im seeing.
