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how do I distinguish beween ho and non ho head

BPB

NAXJA Forum User
I just had a head given to me it is off a 4.0 he didn't know the rear, it was in the 90's. that is good, but how do I rule out that it is a 90. How can i tell for sure that it is the ho head.
 
i believe the HO head (91-95ish?) has the 7120 casting number on the passenger side...? I could be wrong someone else correct me please
 
bigpimpinben said:
mine has the 7120 casting number on it, so it is for sure an ho head?

Yes, it is. Here's the breakdown on AMC242 heads...

#2686 - 1987-1990, "RENIX."

#7120 - 1991-1995, OBD-I HO Head. Noted for raised intake ports (~5/8" inch) and better breathing than RENIX.

#0630 - 1996-1999/2000 (1999ZJ & TJ, 2000XJ) Early OBD-II head. Roughly equivalent to #7120, although the #7120 will edge it out.

#0331 - 1999/2000-current. Later OBD-II head. Can be prone to cracking, and can be readily distinguished by the presence of threaded holes for the coil rail for "distributorless" ignition. May be used on earlier engines.

Note that all AMC242 and 75-later AMC258 heads share a common screw pattern, therefore the heads can interchange. Earlier (say, 75-82 or thereabouts - I'd have to check) AMC258 heads used 7/16" screws, later AMC258 and all AMC242 heads used 1/2" screws.

If you swap your cylinder head for another from a different year, use the head gasket for the head you're using. Note that Fel-Pro P/N 9076PT-1 will work for 1987-2001 AMC242 - probably later, but I haven't checked (this from the label on the head gasket package - I happen to have one that I was measuring to make a torque plate...)

5-90
 
good, I am going to have my rig up and running next weekend. the head that I got is completely dissasembled are there any tech sites that show how it all goes together?
 
Pretty much the exploded view of any OHV head should show you how the valvetrain goes together.

1) Insert the valve from the underside.

2) Install the valve stem seal
3) Set the valve spring in place, and then the keeper on top of the valve spring
4) Using a valve spring compressor, compress the valve spring
5) Using a light magnet or a screwdriver (with grease on the end,) set the valve spring locks in place.
6) SLOWLY release the valve spring, making sure that the locks engage. You really want to do this slowly - as I recall, even with the valve closed, you're still looking at about 140# on the spring...

Repeat for the other eleven valves.

5-90
 
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