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Unread 06-17-2010, 07:17 PM   #1
yjmikea
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1989 YJ Wrangler 
 
Join Date: Dec 2008
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.060 over

has anybody out there gone .060 over on a 4.2 and had no problems running it hard after wards or such i just get a new motor thanks

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Unread 06-17-2010, 07:27 PM   #2
plym49
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1990 YJ Wrangler 
 
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I have no experience going .060 over on a 258.

However, my personal guideline on overboring is that, unless the engine is question is known to have thick-wall castings that can accept overbores of .060 and above, if I need to go bigger than .030 over, I sleeve the cylinders back down to standard.
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Unread 06-17-2010, 10:47 PM   #3
BlackRhino
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1991 YJ Wrangler 
 
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I wouldn't imagine having any problems going .060 over. The 4.2L isn't exactly a high compression engine. I had my 2.5L bored .060, it was worn out by .045 as it was.
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Unread 06-17-2010, 10:52 PM   #4
YJake
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Quote:
Originally Posted by BlackRhino View Post
I wouldn't imagine having any problems going .060 over. The 4.2L isn't exactly a high compression engine. I had my 2.5L bored .060, it was worn out by .045 as it was.
Did that extra compression turn the squirrels into prairie dogs?

Jake
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Unread 06-17-2010, 11:06 PM   #5
BlackRhino
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Quote:
Originally Posted by YJake View Post
Did that extra compression turn the squirrels into prairie dogs?

Jake
lol. The .060 bore made absolutely no difference in terms of power
I only did it because the cylinders were already worn by .045
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Unread 06-19-2010, 08:01 PM   #6
Castr8r
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2006 LJ Wrangler 
 
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.060 overbore is OK. If you want to go further than that, it's a crapshoot. I've read of going .120 over sucessfully, but you need to have a spare block on hand. You can bore it all you dare to and it won't raise compression one bit. Compression is raised by shaving the heads or milling the top of the block.
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Unread 06-19-2010, 10:23 PM   #7
boyce1911
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1977 FSJ Wagoneer 
 
Join Date: Jun 2008
Location: Kingman, Arizona
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My 4.2 is .060 over and Ive got almost 200 miles on it. I know its probably not long enough to tell yet but so far no issues. We'll see this summer if Im going to have temp problems.
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Unread 06-21-2010, 06:42 PM   #8
yjmikea
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1989 YJ Wrangler 
 
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thanks guys im still on the fence weather to rebuild the 4.2 or go for a 3.8 or 4.3 gms but there running high in the dollar department ????
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Unread 06-21-2010, 08:00 PM   #9
RoverJeep90
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1990 YJ Wrangler 
 
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Location: Columbia, Maryland
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I rebuilt my 4 cylinder in my 1990 and went 0.060 over and have had no problems so far. Based on others have said, I'm guessing that it'll be just fine. Personally I'd say just go with rebuilding what you've got. If I were faced with the decision again, I'd upgrade to a 6 cylinder, but I'd still rebuild all of it anyways. So, to me it boils down to whatever work you want to do after the rebuild. I'd rather just put it all back together knowing it was new than have to weld new mounts and fish through wiring. But then again I can't weld, so that probably has something to do with it. Either way, you'll be happier in the end with the new motor!
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Unread 06-22-2010, 08:33 AM   #10
bilwil
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1987 YJ Wrangler 
 
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Mine came with a mopar rebuild with 90,000 on it. semes they were all .040 over and .010/.010. Next motor will be 4.6
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