I don't now what grade the original bolts were but I have been runing an original factory bolts in my 312 with a 406 Galaxie clutch since '65. Used to launch it at 5,500 rpm at the Alton Dragway with 7" cheater slicks. Most everyone I ran had to try to catch me and never had a clutch bolt problem.

The higher the grade, the more brittle. Over torque or yield a grade 5 or 8 and you are asking for problems, they will pop the heads off. A grade 2 will accept the stretch. However, I am not saying a grade 2 is stronger than 5 or 8, but in some circumstances they can be more forgiving. It all depends whether they are torqued properly or not.

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

Check the parts vendors for the correct bolts. Also check out small block fords or FE's as these may be the correct size and length. Aftermarket guys like ARP may have them. Even a scrub may be the same.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Pete, I don't think there's anything inherently wrong with grade 2 bolts, they just don't have the same ultimate strength in tension that grade 5 or grade 8 bolts have. I do know that grade 2 bolts must be used in certain situations. I'm aware that grade 8 bolts don't tolerate bending and are not as tough as grade 5 or especially grade 2 bolts, even though they have a higher yield strength.



For example, I would never use grade 8 bolts to bolt a transmission to a bellhousing. Eventually they'll start breaking.



People use grade 8 bolts indiscriminately and then wonder why their bolts break.



Anyway, I'm going to keep scrounging. I just realized that the pressure plate bolts have a small shoulder under them. I'll either find some used ones or go to the hardware store to try to score something similar.

Best regards,



Paul Menten

Meridian, Idaho

Grade 2 bolts are not  very strong  as a mechanic I wouldn,t use anything less than a grade 5 with sae markings on them a grade 2 bolt can,t take the pressure or torgue for any lenth of time  and is not ment for that application  body and dash parts maybe  be safe and use a grade 5 or 8  shakey Pete

Hi John. Thanks for that info. I think I'll favor the reduced notch sensitivity of the grade 2 blots over the clamping strength of the grade 5's and call it good. I've never seen nor heard of problems there. I'll use some blue locktite to prevent any chance of loosening.



Ford used an interesting variety of bolts on those 50's engines. I've seen grade 4 and grade 6 bolts.

Best regards,



Paul Menten

Meridian, Idaho

Paul:

Original bolts don't seem to have a head marking, which ususally indicates grade 2.  They do have a little extra unthreaded grip length to better center the presssure plate on the flywheel.  The ones that came with my Schieffer aluminum flywheel years ago were grade 8 with the extra grip length, also had 9/16" hex heads instead of 1/2".

John - "The Hoosier Hurricane"

Paul,

      They'll be at least grade 5's. maybe 8's.

Frank/Rebop

Bristol, In ( by Elkhart) 

I can't tell by looking at some of the old bolts from original pressure plates whether they are grade 2 or grade 5. I am inclined to use grade 2 but I thought I'd ask before I stab an engine back in tomorrow.

Best regards,



Paul Menten

Meridian, Idaho