Arp head bolts

[C1Nelson]

Saw a post that was made several years ago that talked about ARP head bolts that were a better bolt for length, straightness, etc. I looked at the ARP Bolt web site and I did not find a kit for the Model A motors. Does anybody know if they still make kits available?

Thanks guys.

[alexiskai]

I contacted them last year, they don't make a kit. You can buy ARP double-ended studs that are the correct thread, length, etc. for the Model A, but:

• you have to buy them individually
• they look a little weird installed
• they're much more expensive, like 3-4x the cost

I haven't heard any complaints about the studs that the vendors currently sell. One nice thing about the vendor studs is the thread fit is class 3, or at least close to it.

I have a sample of the correct ARP stud at home, I can try to find a picture.

[alexiskai]

OK, this is a picture from a conversation I had with Larry Brumfield about 18 months ago before he passed away. Top stud is ARP, middle stud is Snyder's Grade 8 short stud (i.e., not the water outlet or the ignition cable clamp stud). Ignore the bottom stud.

My notes from that conversation:

• The shoulder on the Snyder’s stud measured .43" in diameter, the ARP shoulder measured the full 7/16".
• The coarse-threaded length of the ARP stud is slightly shorter than the Snyder’s stud, but the ARP stud has a longer sloped portion, which I assume is meant to fit a deeper chamfer. On both, the threads + the chamfer are 3/4”.
• The finish on the ARP stud is very smooth

Larry's response:

There are small tolerances in the length dimensions on the 3/4” length which are no problem. For Model A purposes, the Snyder stud will work but it is a poor choice. That stud was made with the whole body at the correct size for thread rolling, which is smaller and has to be smaller than 7/16” for the metal to be displaced and come out to 7/16” on the threads.

Unlike correctly made Model A studs, that shoulder will allow more lateral movement between the gasket and the stud, which is not good. Since the Model A does not have precision dowel pins like a more modern engine, the head and gasket must rely on the clearance between the stud hole in the head and the gasket and the stud for alignment. The Snyder stud is cheaper to make, as the studs made more like the original Ford studs are extruded to allow only the threaded area to be the correct size for rolling, with the remaining size at 7/16” in the unthreaded area. On ARP studs that is the whole unthreaded area, and on the original Ford stud it is an inch, which is plenty.

ARP studs are great studs, but they are overkill for a Model A in my opinion. To have the best results with ARP, their lube [ARP Ultra-Torque] needs to be used and with their lube being used, the correct amount of reduction in torque must be determined. That would take considerable testing and analysis with a Model A and its thick yieldable gasket to have reliability and no blow-outs. In addition, I could see how the block threads in a Model A could be adversely affected, with a straight pull or axial load, with an ARP stud and their lube on the NUT thread end if the torque was a little too high. It is also my understanding that the nice looking black finish on ARP fasteners needs THEIR lube to properly overcome the friction with their fancy finish.

So in my opinion, the best choice for a Model A requiring torque greater than 55 pounds is a plain steel finish, good Grade 8 stud with at least a small shoulder (unthreaded area) at a full 7/16” diameter at the gasket area and a little above and lubed with some gear oils, as they won’t squeeze out, but motor oil still works well and everybody has it. Plus, reliable torque amounts that have been proven for many years.

[alexiskai]

Couple more notes, I believe the ARP part number is AP3.750-1SB. And I rechecked the pricing and it's not that bad, you could get a set of ARP studs and grade 8 nuts for maybe $80-90, compared to a set of standard studs and nuts for $50.

[Jim Brierley]

The ARP studs are absolutely the best, but are expensive and not really needed. Original Ford studs are the equivalent of grade 5, and are good enough for the job. If you want ARP, contact Red's Headers. I don't know if they have a dedicated kit for the Model A, but I'm sure they can put one together. [email protected]

[johnneilson]

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Originally Posted by Jim Brierley

The ARP studs are absolutely the best, but are expensive and not really needed. Original Ford studs are the equivalent of grade 5, and are good enough for the job. If you want ARP, contact Red's Headers. I don't know if they have a dedicated kit for the Model A, but I'm sure they can put one together. [email protected]

Jim,

forgot to mention that the kit made for your head is different than a stock Mod "A".

J

[alexiskai]

Red's Headers Model A ARP stud kit, $125
https://reds-headers.net/index.php?m...p7rk25r2fl2vs0

Just eyeballing it, these appear to be longer than standard. You'd have to ask them for details.

[denis4x4]

I’m using ARP studs, washers and chrome acorn nuts on my ‘31 engine in the hot rod roadster. They also have hex head fittings on the top of the studs for easier installation.

[Jim Brierley]

Originally Posted by johnneilson

Jim,

forgot to mention that the kit made for your head is different than a stock Mod "A".

J

I did not forget, Victor is an ARP distributor, so can make any assortment needed. I'm old John, but not that old!