anybody used a 4.2 jeep crank in a 4.0?

bill jones · Post by **bill jones** » Tue May 31, 2005 5:27 pm

-I wondering if anybody has used the 3.895" stroke crank from a 258ci. (4.2L) 6 cylinder jeep in place of the 3.425" stroke of the 242ci (4.0 jeep).
-I have been told that the crank snouts are the only difference and my bearing book shows they use the same main and rod bearings.
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-So I'm interested in knowing if the crank will swing the rods past the block, cam and pan etc OK and if the flywheel flange and flywheel bot patterns are the same.
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-If this is a fairly straight forward deal that only requires some grinding for clearance, then buying the custom pistons don't bother me at all.
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-I'm also curious as to how the drivability is with the extra 34cubic inches and if there was any problems with the EFI fuel management.
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-We don't intend to change the head and it has little bitty exhaust ports but I have perked it up some.

Ken_Parkman · Post by **Ken_Parkman** » Tue May 31, 2005 11:40 pm

I have no direct experience, but I am told it is quite easy. A friend has one in his Cherokee, it is common enough I believe there are no major issues. I think even the piston issue is quite easy to solve as the 258 has a shorter rod. I *think* you can use the 258 crank and rods directly with a set of 4.0 pistons, but I am unsure of what deck clearance and compression results.

Some people on the AMC forum have done it, maybe you could find someone with direct experience over there?

http://www.amcforums.com/cgi-bin/yabb/YaBB.cgi

bill jones · Post by **bill jones** » Wed Jun 01, 2005 12:01 am

-I have full intentions of using the 4.0 rods, I've already lightened them and polished the beams and shotpeened'm and balanced'm.
-I have a set of off the shelf pistons figured out that will fit the rods and the longer stroke and get the compression ratio right where I want for this altitude (4200 to 7500ft).
-I'll look at the amc forum and see what I can learn there in a few days as I'll be out of town until friday.
-Thanks for the link,,,,

Ken_Parkman · Post by **Ken_Parkman** » Wed Jun 01, 2005 12:05 am

The AMC forum has recently been reincarnated, so historical data has been lost. But for sure some of the members have done it.

340Cuda · Post by **340Cuda** » Wed Jun 01, 2005 8:52 am

Bill,
My son has done this, it was not too tough. I'll ask him to send you an email about it. Is your email in your profile here still good?
Bill Lamb

bill jones · Post by **bill jones** » Wed Jun 01, 2005 11:14 am

-yes sir it is still the same and I appreciate the help.

340Cuda · Post by **340Cuda** » Thu Jun 02, 2005 1:38 pm

Your Welcome!
Hope he was able to help.
Bill

Don Terrill’s Speed-Talk

anybody used a 4.2 jeep crank in a 4.0?

anybody used a 4.2 jeep crank in a 4.0?

Stroker Jeep