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Unread 02-23-2009, 02:33 PM   #1
bigrobby
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.060 overbore ok in 4.2?????

1990 yj 4.2 190k

we're tearing down the 4.2 and have plenty of power adding plans....but my only question is how much can i safely bore it out?

well...is .060 ok???

i'm pretty sure there's plenty of meat on the cylinder walls for .060 but my machine shop guy wants me to check with some people and make sure that much of an overbore didnt cause overheating problems.

anyone know????

thanks

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MY THEORY OF PERPETUAL SPENDING: if i've built my drivetrain strong enough to where i can't break it anymore, i clearly don't have enough power. Strokin' is in the future.
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Unread 02-23-2009, 02:37 PM   #2
jgillespie
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the highest amount i've seen was boring .030 over.
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Unread 02-23-2009, 02:44 PM   #3
Chris
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I am at .040 now and no issues of any type. When I was talking to my machine guy he said he could do more but didn't recomend it.
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Unread 02-23-2009, 03:24 PM   #4
bigrobby
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do either of you have the 4.2? i thought your years had 4.0's.....which is actually whats in my other jeep. the 4.0 has a much bigger bore to begin with....and i suspect since the block is very similar that the 4.2 has more meat to bore out.

a 4.2 bored .060 will still not be as big of a bore as a stock 4.0.
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92 yj, 4.0 H.O. with crane cam 753901 and lifters/ ford 8.8 track lock and disc rear/3.73/ 231 HD chain & sprocket/ Teralow HD SYE/Tom Woods DS/ bout 4 inches mixed susp lift/ 33" BFG muds/ crapload more.

MY THEORY OF PERPETUAL SPENDING: if i've built my drivetrain strong enough to where i can't break it anymore, i clearly don't have enough power. Strokin' is in the future.
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Unread 02-23-2009, 03:45 PM   #5
Chris
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I have the 4.0, I didn't know they were much different. I would just call a couple machine shops and see what they say.
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Unread 02-23-2009, 05:45 PM   #6
RoverJeep90
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I don't know if it means anything, but I went 0.060 over on mine. Guy at the shop did it with no worries. Granted, mine is a 4 cyl, but if you're asking if it's out there, then yes. Check a Haynes manual for the actual specs on your motor, then calculate a percentage increase for the bore. With your numbers, talk to the dealer, as they might be able to pull up some stress specs for your block and possibly check your figures.
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Unread 02-23-2009, 07:44 PM   #7
shaggyjim
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Check this out it might help....http://www.jeepstrokers.com/forum/
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Unread 02-24-2009, 07:25 AM   #8
wendell
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I didn't have mine bored, but did add a holley 470 4 barrel, offy intake, comp cam, header, HEI and MSD. "wow", what a difference. This summer it's getting a 4.0 head from clearwater and rollor rockers. I don't know what other plans you have for your 258, but they will make some power with the right parts.
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Unread 02-24-2009, 01:05 PM   #9
jsawduste
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did .080 on my 93 block 4.0 stroker build. But why .060 ? is the block that worn to need it ?
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Unread 02-24-2009, 01:08 PM   #10
bigrobby
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we've already got the MPI for the 4.0... we're putting in a 4.0 High output head, header, exhaust, intake, head ported and milled. slight decking of the block. Crane cam 753901 (have that in my 4.0...awesome cam!) even goin to the stock 4.0 cam would be a big difference but we're goin all out.

and if we bore it .060 it will be close to a 4.4 liter. with all the 4.0 goodies and performance cam.

now my 4.0 with all the goodies is very strong. using our best dyno flywheel recalculations my 4.0 is running around 265 ft/lb torque and 230 hp. even 4 inches up and 33's that jeep DESTROYS stock 4.0's every time i pull up next to one. I'm expecting this build to be quite a bit stronger
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92 yj, 4.0 H.O. with crane cam 753901 and lifters/ ford 8.8 track lock and disc rear/3.73/ 231 HD chain & sprocket/ Teralow HD SYE/Tom Woods DS/ bout 4 inches mixed susp lift/ 33" BFG muds/ crapload more.

MY THEORY OF PERPETUAL SPENDING: if i've built my drivetrain strong enough to where i can't break it anymore, i clearly don't have enough power. Strokin' is in the future.
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Unread 02-24-2009, 01:11 PM   #11
bigrobby
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Quote:
Originally Posted by jsawduste View Post
did .080 on my 93 block 4.0 stroker build. But why .060 ? is the block that worn to need it ?
no .060 just to add a little displacement. on one hand the difference in displacement between that and say .030 overbored may not be noticeable......on the other hand...if it's as safe to go .060 as i think it is......then why not?
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92 yj, 4.0 H.O. with crane cam 753901 and lifters/ ford 8.8 track lock and disc rear/3.73/ 231 HD chain & sprocket/ Teralow HD SYE/Tom Woods DS/ bout 4 inches mixed susp lift/ 33" BFG muds/ crapload more.

MY THEORY OF PERPETUAL SPENDING: if i've built my drivetrain strong enough to where i can't break it anymore, i clearly don't have enough power. Strokin' is in the future.
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Unread 02-24-2009, 06:49 PM   #12
jsawduste
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Quote:
Originally Posted by bigrobby View Post
no .060 just to add a little displacement. on one hand the difference in displacement between that and say .030 overbored may not be noticeable......on the other hand...if it's as safe to go .060 as i think it is......then why not?
Well you will unshroud the valves a touch. But not enough to make much difference. Simply have the block sonic checked to see how much meat is in it.
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Unread 02-25-2009, 11:22 AM   #13
bigrobby
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if anyone's interested i got a real answer from a guy who used to race them. as i suspected...boring the 4.0 has its limits....they try not to push it too much for motors built to run hard

however ...the 4.2 DOES have quite a bit of meat in the cylinder walls. he said on racing motors, they'd bore them .080 or .100....keep in mind those motors were under tremendous heat and stress.

i'll be going with .060 for one simple reason....going any bigger will take custom pistons which i dont wanna pay for.
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92 yj, 4.0 H.O. with crane cam 753901 and lifters/ ford 8.8 track lock and disc rear/3.73/ 231 HD chain & sprocket/ Teralow HD SYE/Tom Woods DS/ bout 4 inches mixed susp lift/ 33" BFG muds/ crapload more.

MY THEORY OF PERPETUAL SPENDING: if i've built my drivetrain strong enough to where i can't break it anymore, i clearly don't have enough power. Strokin' is in the future.
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Unread 02-25-2009, 04:40 PM   #14
laybackman
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Going .060" over can always be a possible cause for problems in any motor. The biggest problem is what they call "core shift". When the sand castings for the engines are made and them assembled the happy worker in the foundry may not always align the sand core casting for the cylinders centered perfectly in the block sand casting. So when the metal is poured the cylinder walls, (inner water jackets) are not all the same thickness. If they are off centered then you will have a vertical section of each wall that is thinner than the rest of each cylinder. So when you punch that bad boy out 060" you can end up with a motor that has cylinder walls that have no meat left in them in one section.

They can test a block for core shift using sound I beleive. I forget the name of the test or the name of the tool they do it with. It is worth the money in my opinion. IF your machinist does not know what core shift is....find another machinist.
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