crankshaft journal scratches

[nascarmikeb]

I have a 350 4bolt that has a knock in lower end. I removed oil pact to inspect rod journals. Upon removing rod caps, on one of the journals I notice a definite scratch/cut going around the journal. When I do the "fingernail test" my nail can barely feel the "scratch"

My question is, what is the maximum tolerance for such a scratch if a tolerance is even acceptable here. There may be no room for any type of scratch on the journal. Just trying to figure out if I do need to have it ground. It is a scat crank. standard stroke, has not been ground before.

Also, when inspecting the rod bearing, I do not observe any "visible" signs of wear. I do intend to get some plasti-guage to check the clearance to determine how much wear there is.

Mike

[MikeB]

A scratch that you can barely feel with your fingernail is no big deal. And all of the rod bearings look OK?

Maybe the knock is not from the bottom end. Are the flexplate or flywheel bolts tight? If auto trans, is the torque converter tightly bolted to the flexplate?

How about the damper? Does it look OK and is it bolted on tightly?

No valve train noise?

Last resort might be to look at the pistons.

[nascarmikeb]

you know when i was unbolting the torque conveter from the flex plate it only had 2 bolts in it. The other 2 were tight but it was missing a third
wonder if that could have been an issue.

no noise from valve train at all

flexplate bolts were extremely tight, had to use plenty of torque to get them off

yes rod bearings showed no significant or abnormal wear or scratches. I will take pics of them and upload them for you to look at if you dont mind

mike

[71swb4x4]

Originally Posted by nascarmikeb

you know when i was unbolting the torque conveter from the flex plate it only had 2 bolts in it. The other 2 were tight but it was missing a third
wonder if that could have been an issue.

It would not surprise me one bit if you just found your knock.

[MikeB]

Originally Posted by nascarmikeb

you know when i was unbolting the torque converter from the flex plate it only had 2 bolts in it. The other 2 were tight but it was missing a third
wonder if that could have been an issue.

Hard to say, but easy to find out.

Knocking could also be a broken piston slapping around. Ouch!

I remember back in the day when guys would run forged pistons with .006" clearance or more. Those things would rattle and knock terribly until the engine warmed up.