Did I nuke my main bearings? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 10-07-2016, 07:42 PM   #1
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Default Did I nuke my main bearings?

After getting the bearing surfaces on my crank polished I did an initial install with plastigage to check clearance. I torqued everything down to spec in the correct sequence then removed all the caps to measure. I all 5 main bearings were at 0.002" which is slightly outside of standard but still within the service limit of 0.004" Being satisfied I cleaned the plastiage off and applied more assembly lube. then re-torqued everything. The engine sat covered, dry inside for about 8 months. I went to pull the crank for more work to get done to it and noticed the mains looked like the picture. I am using ACL race bearings so I am not sure if this is just a coating that comes off during break or if I did actually damage them just by rotating the crank by hand?

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Old 10-08-2016, 09:52 AM   #2
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To me it looks like there was some grit/dirt on either the bearing surface or crank journal, possibly the crank since it was just worked on. When you turned it over by hand it made those scratch mark as they're in the same path the way the journal rotates. Obviously it wasn't an issue by running the engine since it was still disassembled. In general I don't know if that coating would come off during break in. IIRC the coating does wear off and you have to factor in a bit more clearance for when it does if your blueprinting.
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Old 10-08-2016, 05:45 PM   #3
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Ya, you had dirt.
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