Help Replacing Rod Bolts/Balancing Lower End of Motor

Looking to have the lower rotating assembly balanced in a SB. Original connecting rods will be used with new forged pistons (new main and rod bearings). I'm told that many engine builders will re-hone rods when new bolts are used. Common practice? I was also told that if I balance the rotating assembly with the stock rod bolts and change them out after balancing over config will change slightly. For example ARP bolt heads are different from stock. Looking for input on what should be done. Should I just purchase new rods? Replace bolts/hone, do not replace connecting rod other? Not sure if a manufacturer has exact replacement rod bolts to the originals.

Thank you in advance for your feedback!

I don't know about the re-hone, but as far as balance goes you can check the weights of the old bolts vs the new one and see if you really have a problem. There is likely some variation so you will want to keep them matched to the rods.

Do you brush you teeth before dinner or after?

What kind of driving are you doing with the engine? Nothing wrong with stock rods. Resize the rods, you are doing everything else. Yes they need to be done after ARP bolts installed.

Do ALL your machine work and parts replacement, then balance it last.

Mostly street use to/from various car shows. Not much drag racing with this motor.

Is it a common practice to replace the connecting rod bolts during an engine rebuild, if visually no damage to the stock bolts?

Yes. But use quality bolts. There is lots of cheap junk out there. if they were to visually look bad they would have already failed. If they are rust pitted, or have damaged threads replace them. If you don't know where they came from replace them. You don't want to use a die or thread file on rods bolts, they have rolled threads.

You want to replace everything else and cheap out on rod bolts and resizing?

I always use ARP rod bolts in any hi-perf build, whether raced or not. Cheap insurance in my opinion.

Like said before, the rods always need to be resized after new bolts are installed and balancing is done last.

I agree. Cheap rods bolts don't save anything, they are not worth the effort.

If you replace the rod bolts it would be wise to have the big ends reconditioned. Common sense tells us the big end will change dimensions when the new rod bolts are installed (pressed in).

& HF has a $9.95 digital scale that is just as accurate as my now deceased buddys high dollar one was. suspending the rod ends horizontle is tricky but search it & the other parts (pistons/pins/rings/locks (if used)? bearings weighing/comparing is easy, weigh em & compare to the old stuff. You can trim the rod big/small ends appropriately as needed. read up on it (youtube/google)

Or if a guy has a good paying full time job then move forward right now and have it done at a quality machine shop.

I have a buddy who put his ARP rod bolts in himself. It was his first rebuild and didn't ask any questions. Motor ran really good for about half a season and kicked a rod at the finish line. He wasn't aware that ARP bolts are press in. He just ground them down a little and pounded them in with a hammer.

Don't do that, have a machine shop install them.

I would replace the rods with new Scat rods. Part # SCA-26123, $330. 130+ grams lighter, 7/16" bolts, 4340 steel. Machine shop will probably get $25 a rod to resize and $100 for wave lock bolts and you still have a 40+ year old set of worn out rods.

If I’m going to replace the connecting rods, are the H-Beam style connecting rods with 3/8” bolts overkill for a 340 motor (stock crank)? I’m targeting 10:1 (or slightly under) compression.

You need look no further then at a oem rod and cap fitment vs one that has been properly resized and fitted, a world apart.

If your gonna do the balance job the thought of a light weight scat I beam rod with good bolts at $329 (good to 500 plus) gets alot lighter assembly and takes out the common weak link, the oem rod.

As mentioned, you can buy a scale and get the rods all the same yourself which would help save on the balance job.

Also there are re con older trw sets of rods to be bought for $100.

But why skip on the thoughts you have on your current rods? Nothing like seeing a show car on a flat bed to make every chevy guy smile.

A smart cookie could if they picked the right piston, ect and balanced there own rods could hit the cranks oem target weight and forgo the cost of the balance.

I just did it with a thin rod 318 with replacement trw forged, vs removing 5 grams from the big end of 7 rods I added 5 grams to make them all equal and it also made the oem bobweight work.

Long story short, dont skimp on the rods and bolts, sound like your doing so much right on your project.

Good luck.