1931 Series 60 Cylinder head bolts

[355C]

We just removed the head to work on the valves and noticed someone replaced the head bolts using Grade 8 bolts. Or, should they be studs?

 

I'm under the belief these are not correct - any ideas?

 

Eric

[Robert Engle]

In my opinion, grade 8 requires higher torque to get the bolts to the proper stretch to remain tight.  I know that original bolts and studs on the 8 cylinder engines  were of a low grade.  The bottom of the heads are always mushroomed and wear the head so there is not a flat surface.  

 

I turn the bottom of the hex to a square surface and I counter bore the heads to accept a flat hardened washer.   Original head torque specs were "use a 9 inch wrench with one hand on the wrench.  60 pounds pull would give you 45ft-lbs.  You want to use the grade of bolt that will stretch at this torque.

 

The torque specs are from the 1932 Specs and adjustments manual.

 

Bob Engle

[Str8-8-Dave]

I would add make sure the bolts are long enough use ALL the available threads in the cylinder block without bottoming.  If they bottom on un-machined iron in the cylinder block you risk cracking.  If you use a bolt too short to make maximum use of threads in the block you risk stripping block threads.  The original bolts were not grade 8 for sure and were not torqued to values used for modern bolts and block material.  Studs might be a safer way to go because you can screw a stud to just reach the bottom of the block threads with less risk of being short or cracking.

Edited December 2, 2021 by Str8-8-Dave (see edit history)

[EmTee]

3 minutes ago, Str8-8-Dave said:

If you use a bolt too short to make maximum use of threads in the block you risk stripping block threads.

 

Though not original, for the reason above I'd seriously consider using studs rather than bolts.

 

39 minutes ago, Robert Engle said:

I turn the bottom of the hex to a square surface and I counter bore the heads to accept a flat hardened washer.

Studs/nuts, especially when installed with the washers as above, provide better control of torque (i.e., the clamping force) than bolts do.  I don't know what size and length are needed, but seems there should be something off-the-shelf that can be used or modified to work.

[Robert Engle]

Most of the block threaded holes are Through holes.  There are only 2 or 3 that are blind holes.  You will  not be able to remove the head in the car without double nutting the top of the stud.  In my opinion using all studs is over thinking the issue.  Low compression engines that have used bolts for 90 years don't need to be changed.  Grade 1 bolts at 45Ft-lbs torque will do just fine.  I do recommend applying Permatex Forma gasket to the studs bolt thread that go into the water jacket.  Modern bolts will have a larger head than the original headbolts.

 

Bob Engle 

[EmTee]

My main reason for suggesting studs was to avoid damage to the threads.  If the threads are OK, then 'six-of-one, half-dozen of the other'...

Hopefully the head doesn't come off again for at least another 80 years. 

[32buick67]

Its mindblowing to think about all of the characters who have worked on our cars over the decades to keep them working in mostly original condition, and maybe even crazier to think about those who might be involved with the cars in the future....its ideal to keep cars in the family, but I think for the best interest of the car, its probably best to find someone with the aptitude, passions and strong interest to keep things rolling.  If that is a family member, then all the better!

[Mark Shaw]

Eric's question has been answered....