ARP head bolts

Last time I assembled my engine, I used standard grade 8 bolts for the head. However, I had read that grade 8s (especially those made today) may not be the best choice for head bolts because they don't stretch properly. Not sure if that's true but I did notice that the threads were ruined on most of them when I took them back out so I decided to find some good head bolts and found these from ARP http://www.summitracing.com/parts/arp-hap4500-5

They are pricey for sure but I ordered some. The description says they are stainless steel but that's not true, they are chromoly. They look more like the factory head bolts how the shank widens at the top. However the hex head is only 1/2" (the grade 8s have a 9/16" head.) Why would the hex head be so small? Is that a risk when torquing them to 75 ftlbs?

 

ARP are highly regarded and should be top quality. The smaller hex head may be an advantage in restricted spaces.

The only downside I can see is that the socket wrench must be strong enough. but 75 ft lbs is not a huge amount. Use a "six-point socket, and/or you can use an impact rated socket if you want to be double sure.

 

The entire load on the ARP's is on the flange, not the driver head, so as long as the hex is big enough not to strip, there isn't a problem. As pointed out above, the smaller size is an advantage in tight spots. I would never use a plain bolt, grade 2 or grade 9, for head bolts. Just not designed for that. Way better off using good used real head bolts than than a regular bolt.

 

Grade 8 bolts if there quality US made bolts are the same as they always have been, but using standard bolts that are not designed for head bolts is never a good idea.

 

OK thanks for the information, it just caught me by surprise that the hex head was smaller than the originals and the grade 8s. I can definitely tell they are high quality bolts and may be worth the money.

 

It may be a flange head bolt, sort of like an integral washer.

 

I went to the ARP website and read this, which explains that they design them with smaller heads so you can retorque without having to remove the valve train. Not sure if this will work in the Willys F Head but at least I know it was intentional. From the ARP catalog:

High Performance head bolts are available with a reduced wrenching hex or 12-point and wide area flanged head that eliminates the need for valve train removal to facilitate cylinder head retorquing.

 

I run all ARP hardware in my blown big block in my jet boat(800 HP). You can't go wrong with their stuff.

 

Bolt torque is actually a calculated function of bolt stretch. Think of a bolt as a spring.. The more torque, the more stretch, the more clamping force until you exceed the yield strength of the bolt. Once you reach yield the bolt will experience plastic deformation and loses it's clamping force.

Anyhow, ARP is good stuff.. It will serve you well.. Just remember to lube as they reccomend as this has a major impact ont he stretch/torque ratio...


Bubba