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.