"light" 1984 258 block

casw

Active Member
Joined
Jul 4, 2009
Location
Raleigh
I've read that the block for the 4.2L from the early 1980's is a lighter casting (7/16" head bolts) than blocks from both earlier and later years (1/2" head bolts). Is this lighter block still suitable for a 4.0 head conversion?
 
sure, you can get the holes drilled/tapped to 1/2", or there are some centering/adapter sleeves out there so you can use 7/16" head bolts with the 4.0L head.
FWIW, I never heard the block casting was lighter, although that may be true. The big difference is the lighter crankshaft, different casting. To add to the confusion, the YJ 4.2L used 1/2" headbolts, not sure which crankshaft it had.
 
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