head bolt length on a 1939 Cadillac 346

[cadillac751940]

      I would like to know the proper length of the cylinder head bolts for my 1939 Cadillac 346.  Thanks Scott Springer

[Bob Hoffmann CLC#96]

They are approx. 2 5/16". They do extend into the water jacket. I have a set of new bolts I bought years ago. Pre Chinese. They are Grade 8. I have a NOS oil pump plus more flat head parts.  Please contact me directly at bobscads@comcast.net.
Thanks, Bob

[Ron Parker]

The 4 bolts for the water necks are longer and marked with a dome on the head.If used in the other holes they can break the block. I tested corroded old bolts to see how much torque they would take and several broke at 150 lbs with no stretching.

[Tom Beaver]

The original bolts are 7/16-14 x 2-3/8 with an 11/16 head they are non-standard and not made any more except by special order.  The closest Standard Grade 8 bolts are 7/16-14 x 2-1/2 with an 5/8 head.  If you use the standard bolts it's probably a good idea to use a flat washer under the bolt head because of the slightly smaller bolt head and the rather generous hole sizes Cadillac used for the heads.  Also, the washer would shim the bolt out some to help limit thread protrusion into the water jacket.  However, you need to be careful what type of flat washer you use.  APR makes special hardened flat washers for head bolts, they have  a chamfer on the upper ID in order to clear the radius where the bolt shank transitions to the bolt head.  They make ones with a 7/16 ID, 3/4 OD and come in three different thicknesses.  They also make special studs (Part No. AJ5.150 -1B) that will fit the Cadillac manifolds, they are slightly longer than the stock studs but are the closest fit I've found so far.  Also, as Ron pointed out, the four water neck bolts are longer than the rest of the head bolts and I have not tried to find a modern replacement for them.

Tom Beaver

[cadillac751940]

   Thanks guy for all that good information it's been a great help.   Scott

[Bob Hoffmann CLC#96]

I offered a set of NOS bolts to Scott. He respectfully declined. I really appreciate Toms detailed post on these bolts. I have a NOS  set of 38 of the correct bolts. Dry stored for years. $200 post paid in the USA. Please contact me directly at bobscads@comcast.net
Thanks, Bob

[Paul Phillips]

When I did my 41, I chose to use the modern grade 8 bolts.  I also had a machinist make up some 'modified head' bolts of the correct length for the water outlets that replicated the domed feature on the head, but match the 5/8" head of the other bolts.  I think I have a few extras around, if someone is interested.  PM me and we will figure a fair deal.

Paul

[Bobby B]

I used Ford 260/289/302 Head bolts on mine. They measure about an 1/8" shorter than factory length, but had an 11/16" Head. I then filed off the factory stamping on the head. Readily available from AMK products, Part# B-12667.  Purchased through Tony at Restoration Parts Source in Hayward, CA.  I did use my factory water neck bolts because the Ford Big Block Bolts were too Long. Nice to have new.
                                                                                                                                    Bobby