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343 cylinder heads |
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easydean 
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 Topic: 343 cylinder headsPosted: Feb/06/2020 at 1:55pm |
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Do all the 343 heads / #558 use the same head bolts - did some need the stepped head bolts? I was told later heads need the stepped bolts but am not aware of that. Thanks for any and all help. Dean/Fargo
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WesternRed
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Posted: Feb/06/2020 at 4:04pm |
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343 heads use 7/16" head bolts, later dog leg heads use 1/2" bolts, you need stepped washers and stepped locating dowels to install later heads on an early block with 7/16" bolts unless you want to drill and tap the block for 1/2" bolts and locating dowels.
For all heads, the lower row of bolts is shorter than the rest.
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I've finally given up drinking for good...........now I only drink for evil.
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SC397
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Posted: Feb/06/2020 at 4:38pm |
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The 1968 and 1969 343 use 7/16" flanged head bolts like on the left. The 1967 343 used non-flanged head bolts like on the right.
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Trader
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Posted: Feb/06/2020 at 4:56pm |
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For a rebuild, my opinion would be to use heavy, small diameter, grade 8 washers under a head bolt posted on the right.
Putting later heads on an early block, you should be using step washers and studs. Correct engine studs are rated for a higher tensile strength, can be reused and produce a better clamping force. |
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BassBoat
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Posted: Feb/08/2020 at 7:08am |
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One of my sayings is "just because you get away with something, doesn't mean it was smart". So I'm willing to change my mind, but I never had a problem with later heads on early blocks using the stock 7/16 bolts. Looking at Rick's picture, I always had the flanged style bolts, didn't know that there were two types before either. Never heard of stepped washers until the Edelbrock heads came out. Seems obvious to me you would need them on the softer aluminum heads. But have people really been using stepped washers on iron heads for 50 years?
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Class Guy
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Posted: Feb/08/2020 at 7:52am |
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This is related but may not answer the question in everybody's mind. I used to race big block Chevies 396-427 in NHRA Stock and Super Stock. it was found while testing on a flow bench that if you moved the head laterally a little (.060') that the intake flow picked up a bit. Also, when using OEM pistons in Stock Eliminator, exhaust valve clearance was extremely tight and we were not allowed to machine the pistons. If the head were moved up on the block surface by a small amount (.060") the exhaust valve to piston clearance was increased by .040' or so and we could increase the camshaft exhaust duration. Moroso sells offset heads bushings in .030" and .060" offset bushings to accommodate this practice. In order to move a BBC head that much the bolts holes in the head had to be enlarged to 1/2" or 33/64". We still used the stock size 7/16" bolts and never had any problems even on 12:1 compression engines. You had to used hardened washers under the bolt head though.
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WesternRed
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Posted: Feb/08/2020 at 7:53am |
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Nah, I do believe you can get away with flat washers or maybe even none, but since you can get the stepped washers now, why not use them.
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I've finally given up drinking for good...........now I only drink for evil.
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SC397
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Posted: Feb/08/2020 at 9:19am |
Yea, I learned the hard way that there is a different torque setting on the 1966-1967 engines vs 1968-1969 and the only difference is the flanged head bolt vs non-flanged. My assumpton is that when the 390 came out in 1968 they changed the head
bolts for all of the V8 engines to the flanged type and bumped up the
torque. 1966 & 1967 Head Bolt Torque Spec. 72-77 #/ft. (7/16" Head Bolts)  1968 & 1969 Head Bolt Torque Spec. 90-100 #/ft. (7/16" Flanged Head Bolts)
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BassBoat wrote: