After considerable thought I've decided to go with the 4.0L head upgrade on my 83 CJ7 4.2L engine and am trying to determine the head bolt size.

I did some research on the block and found it has a block serial number of 012C05

I also found this in another post. The poster said this:

<begin quote>
From 73-86 258's.
1st digit is the year but it doesn't translate directly:

7- 1974
8- 1975
9- 1976
1- 1977
2- 1978
3- 1979
0- 1980
etc....

If this information is correct that would mean my block is either a year 80 or 90?

0=1980
12=Nov
C=2v carb
05=day of the month built

<end quote>

If it is an 80 or 90 engine then the head bolts should be 1/2" rather than 7/16" according to this article:

http://monsterslayer.com/jeep/40Head/40Head.htm

If that is true then I won't need to either drill and tap the block (not planned) or buy a sleeve kit for the 7/16" bolts to up them to 1/2".

Thanks for any help.


BTW, for those who helped and were following my issues with oil on the #2 plug, I'm now seeing fresh oil on the plug threads after I drive where before I didn't. I only saw oil on the threads after it was parked and even then rarely. Now it seems to be getting worse and I'm seeing oil seeping from the head gasket area just below and between the #2 plug and #3 plugs.



Thanks again.

Simple. If you have the 1/2" head bolts a 5/8" socket should be able to fit over the nut of the bolt.

I did the swap about a year ago on my CJ but it has a 1989 Wrangler engine in it with the 1/2" head bolts on it so there was no modification needed. 1987-1990 & (I think) 1979-1981 258's have the 1/2" head bolts. You'll like the added horses after the swap. Good luck!!

Chris

I have two types of bolts on the head that I can see. The bolts with studs are 5/8" nuts like you said. There are other bolts which do not have studs and these heads are smaller than 5/8". However, if more than one is 1/2" then they all must be 1/2". This is good news for me.


Thanks,