Join Date: Aug 2002
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Re: convert 345 to 392
My understanding is the 345 and 392 cranks *are* different, but not by much.
Mostly it's a counter-balance thing since the 392 used 1/4" larger pistons which would naturally weigh more. You can use a 345 crank with a 392 (or vice versa) if you're having everything balanced during a rebuild.
My recently built 345 in my daily driver/trail rig sports a 345 crank, 392 rods, 392 (welded style) rocker arms, 345 (boat style) rocker shaft, 392 pushrods. 345's 2bbl intake and heads.. soon a different 345's modified 2bbl TBI intake and a ProJection.
To turn a 345 into a 392, you'd need to have the engine overbored .250 of an inch. Typically you can't buy anything larger than a .060 piston because the cylinder walls are too thin.
The block castings ARE different between the 345 and 392. If you DID punch a 345 .250 over and didn't run into a water jacket, you will certainly have sacrificed longevity and reliability for 47 cid.
Now, you could definitely take your current 345, and buy just a non-IC 392 *BLOCK*.. buy new pistons, and reuse the 345 crank, rods, heads, rockers, pushrods, etc. That is, if you have the later 345.
There was a change in the very early 70s. There WERE two rods used - a lighter rod for the 345, and a heavier rod for the 392. IH switched to a single common connecting rod for both the 345 and the 392 very early in the 70s (Eldon has posted the exact details on the Binder Bulletin FAQ). Thus, a later (definitely, say, a '77 345) 345's connecting rods should be up to serving in a 392.
Just after I had bought the pistons and they were being fitted to my 345 block, I was at the junkyard looking for a wide T19 when I found a 392.. it wasn't until a little after I realized I should have sent the 345 pistons back, bought the 392 block, and bought 392 pistons and had the 47cid for "free" - or just the price of a bare block and some extra cleaning.