Crankshaft Main Journal Discrepancy?

[sbay]

Hello all,

I’m beginning my engine rebuild journey in the coming weeks due to a spun bearing. I ended up purchasing a used standard crank and based on the colored dots on the crank, my #6 thrust main bearing is dotted green, as is my number #1 main bearing, the rest of the journals are yellow. The issue is when I use a micrometer (for reference, using a calibrated Mitutoyo) I’m getting the proper readings for all the journals except the thrust bearing. My readings are:

1 Green Dot - 59.957 mm

2 Yellow Dot - 59.964 mm

3 Yellow Dot - 59.964 mm

4 Yellow Dot - 59.964 mm

5 Yellow Dot - 59.964 mm

6 Green Dot Thrust - 59.964 mm

7 Yellow Dot - 59.964 mm

As you can see, the reading is matching as if it were to have a Yellow Dot. I’ve checked this over and over and checked the calibration of the micrometer with no difference in result. Of course I will still be Plastigauging, but I’m just confused and wondering if anyone might have any clarity on this? I’ve attached pictures of journals 1 and 6 to display the green dot.

[eacmen]

Full disclosure - I've never done main bearings before.

With that said, at my skill level for rod bearings I always verify clearance with the pastigauge. Plastigauge usage is more “idiot-proof” than other machinist measuring tools.

I cant count how many times I've measured something with a caliper or micrometer and messed up.

Was watching JAMSI YT channel the other day and he went off on how he can't trust any of the parts anymore and has to verify everything before assembling an engine.

I would say good on you for not blindly trusting the dots and you won't really know the real truth until you mate the bearings you get with the crank you have and verify with pastigauge.

[sbay]

Full disclosure - I've never done main bearings before.

With that said, at my skill level for rod bearings I always verify clearance with the pastigauge. Plastigauge usage is more “idiot-proof” than other machinist measuring tools.

I cant count how many times I've measured something with a caliper or micrometer and messed up.

Was watching JAMSI YT channel the other day and he went off on how he can't trust any of the parts anymore and has to verify everything before assembling an engine.

I would say good on you for not blindly trusting the dots and you won't really know the real truth until you mate the bearings you get with the crank you have and verify with pastigauge.

Thank you, yeah I figured more of a wait and see kinda thing with the Plastigauge. Interesting nonetheless…

[bmwfnatic]

The dot on the crank only affected the bearing installed in the cap, the block indicated the bearing installed in itself, therefore they can be different to achieve and optimal clearance.
However I would say on the used crank don't go by the dots anymore, but go by your actual measurements and desired clearances, and pick your bearings based on that.

[sbay]

The dot on the crank only affected the bearing installed in the cap, the block indicated the bearing installed in itself, therefore they can be different to achieve and optimal clearance.
However I would say on the used crank don't go by the dots anymore, but go by your actual measurements and desired clearances, and pick your bearings based on that.

Looks like that’s what I’ll be doing then. I’ll start off with standard main bearings all around, even with the journals that have a green dot, and decide from there based on Plastigauge whether a change is necessary. Thank you for the help!

[sapote]

I’m beginning my engine rebuild journey in the coming weeks due to a spun bearing..

The original bearings spun, how many miles? I just want to know for my data base.

[sbay]

The original bearings spun, how many miles? I just want to know for my data base.

86,468 miles