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Old 06-23-2014, 07:24 AM
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Stock 4.0 Cylinder Dimensions

Hi all.

I am about to remove the pistons from my rod-knockin' 02 X-model TJ with 226K miles. I will be deciding whether to fix the existing knock or replace the short block.

I cannot locate exact cylinder dimensions, so before I go to a dealer, can anyone point me to a reputable link that documents the cylinder specs?

Many thanks in advance!

Rich



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Old 06-23-2014, 08:34 AM   #2
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3.88 bore x 3.41 stroke. Per Mopar Performance Parts, more specific bore size is 3.8759 to 3.8775 for standard bore.

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Old 06-24-2014, 10:56 AM
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Wow DoubleOught. That's great info...I am assuming these would be the correct max & min limits?

Meaning:

Maximum wear out to = 3.8775
Dead-on = 3.8767
Minimum manufactured limit = 3.8759

I'll be taking 9 measurements per cylinder: (top, center, bottom) x (0 degrees, 90 degrees, a third at either 45 or 135 degress).

If nothing is too far tapered or out-of-round, I'll keep the same pistons. Otherwise, I'll either bore out .030 or buy a short block.

Thanks!

Rich

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Old 06-24-2014, 12:37 PM   #4
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I'm thinking that this is the minimum and maximum allowable bore range on a new engine. If you are just going to replace one or two, I would go with standard bore piston and rings, assuming the wall didn't get messed up when the skirt broke. I have read that broken skirts are common on some of them. I've got almost 200K on 00 and I believe our 97 is around 171 and neither use oil so hopefully you can repair it and keep going without a major overhaul.

I've been doing a little research to rebuild a 2.5 for a friend of mine and it appears that SpeedPro makes coated hypereutectic pistons in various bore sizes for the 4.0 and 2.5.
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