AMC 258 Rod journal diameter/need help -
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Unread 01-28-2013, 12:10 AM   #1
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1987 YJ Wrangler 
Join Date: Dec 2004
Location: Longmont Colorado
Posts: 22
AMC 258 Rod journal diameter/need help

I am a bit confused about something I discovered on my 4.2L (i apologize its in a Wrangler, seems to be more folks who know about the 4.2L over here). I have only confirmed the block/head to be from a 1987, the pistons are .030 over through so its been somewhat rebuilt at some point.

We removed the pistons to check the journals and bearing clearances just to check everything out since we also discovered the timing chain had over an inch of play.

We removed the pistons and the rod journal diameter is 2.0855 consistent on all 6. But according to the Jeep Wrangler SM for 1987 the 4.2L rod journal diameter 2.0934-2.0955. I have an old AMC 232-258 engine rebuild manual (got it as a pdf from somewhere, pages number I-a-1-24 if that helps anyone identrify it) that shows that 2.0855 was a standard size and to use .010" for rod bearings.

Just wanted to make sure this is correct and why the rod journal would be that size? possibly from a older 4.2L?


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Unread 01-28-2013, 12:32 AM   #2
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Matt1981CJ7's Avatar
1981 CJ7 
Join Date: May 2011
Location: Elbert, CO
Posts: 15,724
I suspect the crank has been turned .010" under on a previous rebuild. That's pretty common.

Yes, .010" bearings should work. Connecting rod clearance spec is .001-.003".

Good luck.

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