Resizing rods after installing ARP rod bolts

[Pyro15D]

Hey, like the title says, I was wondering why you have to resize the rods when ARP bolts are installed. My thought process is, if they are the correct size to begin with, how does changing the bolts out throw the size out of whack enough to need to be resized? I'm pulling my motor with less than 100 miles since the rebuild out to upgrade the oil system and I figured while I was there, I could do a quick upgrade to the rod bolts. If I have to disassemble the whole engine to do that though, I don't think I will do that.

 

[IJ.]

Knocking the old ones out and pressing the fresh ones in distorts the big end slightly and considering the youngest 7M rods are now at least 20 years old they're probably overdue for resizing anyway.

 

[Pyro15D]

Yeah. Resizing them isn't the big deal for me. The big deal is the fact that the engine was just rebuilt and hasn't even finished the break in and now most of that work would be thrown away to replace bearings that have maybe 100 miles on them. Well, you're right. I've built 220hp aircooled vw engines and 515hp small block Chevy's. I know anything worth doing is worth doing right. It just sucks! FML. Such a waste to replace bearings with so little use.

 

[IJ.]

I feel your pain but the potential for massive fail is high with these engines...

 

[Pyro15D]

Yeah I understand. This isn't just a stock build either. I'm trying to get 450 HP out of it, so I can't take short cuts. I guess I don't want to spend money where I don't need to spend it especially if it could be better used somewhere else. Thanks for the advice though. I needed someone to tell me to not take shortcuts. From the info I've gathered on this forum, these engines aren't as forgiving as aircooled VW's and small block Chevy's.

 

[IJ.]

They're a fussy bitch at the best of times, any shortcut will bite your ass clean off!

 

[Pyro15D]

Yeah I don't want that. Actually, how strong are the stock rods with ARP bolts? What is the accepted power limit? Actually, it would be really cool to have a list of the stock parts and their power capabilities stickied somewhere. That way ignorant people like me would know what does and does nif need to be upgraded to reach various horsepower outputs.

 

[IJ.]

Stock Rods are plenty stout just 20 years old, compare one to a SBC rod and you'll see

Sean/X-Man has taken a set to over 700wrhp.

 

[Pyro15D]

Will do. I know the SBC rods are pretty tough, but then again that was oldschool American build quality back in the day.

 

[Flateric]

This is news to me about the ARP rod bolts. I don't actually understand why resizing would be needed with the rod bolts being made for the job. I don't believe I resized anything when I used ARP rod bolts on my 2j. But Jeff Lange was helping me with the rebuild and I may simply have missed him working some magic at some point involving this. Where did you get the info about resizing being required from?

(edit, sorry IJ, I somehow scrolled right past your reply and explanation the first time somehow, so we are talking bearings being sized properly, correct?)

 

[IJ.]

Making sure the big end tunnels are round and the correct size so you get the proper "crush" required on the bearing shells to prevent them spinning.

Most used engines have egg shaped tunnels, knocking the bolts out/in again stresses the rods changing the roundness of the holes as the bolts have a knurled section for an interference fit.

 

[Pyro15D]

How do they make sure the rod big end is round? I know about measuring it but does the machine shop bore it out or something?

 

[IJ.]

How do they make sure the rod big end is round? I know about measuring it but does the machine shop bore it out or something?

That's what "resizing" is, the grind the partline of the cap making the hole smaller than stock then bore/hone it back to spec.

They will also check the small end bush and make sure it is round and within tolerence.

 

[Pyro15D]

Oh okay. I'm just wondering because where I am stationed, they have a machine shop and I am good friends with the guys that run it. If the Navy trusts them to machine parts for the j52 and t56 engines, then it should hopefully be good enough to do the parts on my engine. They are cheap to do business with too. Anything can be done for a pack of smokes Hahaha.