James_Douglas Posted March 3, 2011 Report Share Posted March 3, 2011 Can anyone tell me what the original head bolt head wrench size was on the flathead six ? I have an engine with head bolts with head sizes in 11/16, 5/8 , and 1/2. They are all head bolts with the under cut shaft and all the original 2-13/16 inch length. I ran across a guy that has some 7/16 -14UNC head bolts that are three inches long with the OLD Chevy 5/8 head on them. I will be getting a price later today. They are not making them anymore and they are not in their catalog. But they are sitting on 1000 of them...and I may be able to get some cheep. Thanks, James Quote Link to comment Share on other sites More sharing options...
Oldguy48 Posted March 3, 2011 Report Share Posted March 3, 2011 I've got a P20 engine sitting in my garage. I just checked the head bolts, and they require a 11/16" wrench. Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted March 3, 2011 Report Share Posted March 3, 2011 11/16" is correct. And the length is 2 13/16" as you mentioned. And as you know the undercut is important. I am sure you also know that the 11/16" head is non standard for a 7/16" bolt. 5/8" is standard. Quote Link to comment Share on other sites More sharing options...
James_Douglas Posted March 3, 2011 Author Report Share Posted March 3, 2011 Thanks guys. The '49 head bolts are a mess and a mix of types. I guess Automotive Engineering did rebuilds in the early 1960's and played mix and match with the head bolts. The folks that sell the Chevy bolts, Pioneer Auto, stopped making the 5/8 head size bolts some time back for the SBC and just do the 1/2 head size bolts now and that is the part number you will find in the forum archives. They have about a 1000 of the 5/8" head version but it is not in their system. I contacted them about selling me about a 100 of them. I should have flathead head bolts for the rest of my days ! If anyone else wants any when they tell me how much and how to pay for them, I will let you know. Best, James Quote Link to comment Share on other sites More sharing options...
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