Engine quick help needed please

[Manic Mechanic]

im rebuilding my 258. long story short my new block is a 75-79 my old one and head is 81-85 i know the bolts on the new block are 1/2" where the old one is 7/16". is there any other differences i need to know before i call my machine shop and just have them drill out the head to accept the larger bolts. or will there be interference issues and or running problems by using a newer new head on an older block. has anyone else had this problem. i assume that all 4.2 are basically the same minus emissions-related equipment. even more so since i see numerous post talking about putting 4.0 heads on a 4.2 so it cant be that drastically different unless im completely mistaken.

thanks in advance for the help and replys

 

[shum8]

Man - Can’t help. Have zero experience swapping 4.2 heads around. I’m sure someone will chime in shortly with something useful....... Unlike me


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[CJ]

I called some one- who may help - lets see..

 

[CJ]

best thread -- >> https://jeep-cj.com/community/threads/4-0-search.23818/

https://jeep-cj.com/community/threads/4-0-head-swap.17553/

https://jeep-cj.com/community/threads/4-0-swap.54091/

 

[Manic Mechanic]

while i appreciate those links they are about swapping a 4.0 head onto a 4.2.

im not doing the 4.0 swap im merely taking the head off my 85 4.2 which uses a 7/16 head bolt and putting it on a older 4.2 block that has 1/2 head bolts. i just told the machine shop to drill em out and use the larger bolts

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[CJ]

while i appreciate those links they are about swapping a 4.0 head onto a 4.2.

im not doing the 4.0 swap im merely taking the head off my 85 4.2 which uses a 7/16 head bolt and putting it on a older 4.2 block that has 1/2 head bolts. i just told the machine shop to drill em out and use the larger bolts

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Oops, my bad - need to better proof / reading. I misunderstood.

Glad you came up with a solution.

 

[Manic Mechanic]

Just hope it's the right one

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[CDT540]

while i appreciate those links they are about swapping a 4.0 head onto a 4.2.

im not doing the 4.0 swap im merely taking the head off my 85 4.2 which uses a 7/16 head bolt and putting it on a older 4.2 block that has 1/2 head bolts. i just told the machine shop to drill em out and use the larger bolts

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That is what i did. Been running fine ever since

 

[Manic Mechanic]

That is what i did. Been running fine ever since

Ty. I assume there's no difference I just wanted to make sure

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[CDT540]

Ty. I assume there's no difference I just wanted to make sure

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Have the machine shop double check push rod length. Seems like I recall the shop having to confirm that but otherwise all good

 

[Manic Mechanic]

I assume they are correct they ordered all new parts and I'm having them do the final assembly

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