cdrod

I'm trying to finish the assembly of my aluminum headed, 375cid SBO stroker motor and have a head bolt/stud question. I purchased a set of ARP head bolts (P/N 180-3700) which does not have a stud for the stock AC compressor bracket to mount (see my first pic). I contacted ARP to see if I could purchase a single stud from them to fit my application. I would need a 5-7/8" long stud with 3/4-1" of course threads at the block end and about 2" of fine threads at the head end; however, the P/N they suggested only has 1" of fine threads - not enough for a nut to contact the head.

Here's my questions for all the experienced CO engine builders out there.
1. Could I use the stock head bolt/stud for this location to mount up the AC compressor and use the ARP bolts everywhere else? The ARP bolts are probably stronger than the stock head bolt. Would there be less clamping force using the stock bolt?
2. Should I be concerned about galling the aluminum head by using the stock bolt without a washer?
3. I could use an ARP washer under the stock head bolt/stud to prevent the galling but this would effectively "shorten" the head bolt and reduce the number of engaged threads in the block. Using the stock bolt with the ARP washer is about 1/8" shorter than a stock head bolt and about 1/16" shorter than the ARP bolt. Would this significantly weaken the clamping force of the stock bolt? My CR will be 10.25:1 (approx.)

Thanks in advance for helping out!

Rodney

This is the bolt/stud I need to mount the AC compressor.


This is a comparison of length using the ARP washer with the stock head bolt.


Same shot as Pic2 but with a straight edge in the pic to assess lengths.

oldcutlass

You can use the stock bolt and arp washer using arp lube torqued the same as the remainder of the arp bolts.

cdrod

oldscutlass:
Even if the head bolt is shorter? I would think the clamping force of the bolt would be related to the number of threads engaged in the block. At 14 threads per inch, 1/8" shorter length means about 1 less thread engaged in the block.

oldcutlass

It will not make a difference.

oddball

1) It'll work fine and clamp much the same if torqued the same. Use the same procedure and same torque as the ARP parts.
2) Meh, I agree with the washer would be better just because the holes may be a bit larger than the stock ones.
3) There's still plenty of threat engagement. Count turns as your run down the bolt.

They have an appropriate 1/2" stud - I'm using it on my 403. I'm surprised they don't have a better matching 7/16" stud!
ARP stuff is stronger than stock fasteners, but we're not approaching the yield of the stock stuff at the stock torque, so it's not that big of a deal for stock-ish builds.

Once you get enough threads to get full engagement (depth == width of fastener, IIRC? maybe a small multiplier like 1.5.. there's a formula out there somewhere that I saw many moons ago) then you're good to go. Any more is just gravy. That does assume a certain thread profile and material strength, but those are normal considerations for SAE threads, grade 8 bolts and cast iron holes.