Looking for engineers and builders to shed a little light for me. I'm currently working on what is basically a G23 project (f23 bottom end with h22 head). I would really like to upgrade the rod bolts, but there are no options from ARP or anyone else that I am aware of. The stock rod bolts are M8x1.25; k20a rod bolts are M9x1.25. Since the thread pitch is the same, I was thinking of running a tap down the threads to bore the rod bolt holes out to M9 size from M8; in theory the tap can just ride down the existing threads. However, I shot an email to ARP to see what they thought, and here is the response I received:

"You would need to drill the existing threads out first and the tapping drill size for the M9X1.25 is close to the major diameter of the existing M8X1.25 threads but it might not quite clean up. The bigger issue is that you are making the hole in the rod bigger and potentially weakening the rod in the process. I would not recommend what you are proposing."

I wanted to see what some of you thought in terms of reliability, particularly concerning whether I will be weakening the rod or not.

 

What they are saying is correct. I worked in a machine shop for a while and we ran into tapping issues like this. You would need to drill the threads out and insure you have the walls cleaned up and that alone would potentiality take you over your M9x1.25 goal. Not to mention you are removing material. So you could possibly get stronger rod bolts but you would still be weakening the actually rod itself. Kind of like where is the reason to upgrade bolts of your going to weaken another aspect of the item your trying to fortify in the first place. You would also need to figure out would it be better to use a roll tap or a cut tap. And unless you have a manual mill that would be a hard task in general. Does golden eagle offer any rod bolts for the F series? Maybe talk to arp about a custom set of M8x1.25

 

^^^^ he is correct. i built a g23 for a friend of mine, and we had to buy after market rods because of this. what are your plans for the water pump?

 

sounds costly to me. why not just get some rods and use the arp2000 bolts that are included in most rod combos?

 

Wow, back from the dead. The reason I didn't get new rods was because the only company that made f23 rods was Crower at $800/set which was out of my budget. I did end up getting a special order of bolts from ARP for about a dozen sets and sold the rest off.