Gsoleski

I will be installing arp rod bolts in my 350 build but i've heard you want to get the rods re sized after this. My question is what does this do to the bearing clearances? Does the shop take off a thousandth or two when they do this? My crank is already undersized 0.010 so would I have to get bearings that are 0.012 bigger if those even exist?

ibmtech

iTrader: (1)

I don't see what having to resize the rods or changing the main bearings has anything to do with ARP bolts. To my understanding ARP bolts have a fatigue strength up to ten times higher than regular bolts. You use the Main bearing tolerances for your crank ~VS~ block which has nothing to do with the Rod Bolts. And Rod length only effects how long the piston stays at TDC. I might be wrong, but don't think so.

Apeiron

Popular wizdom says they should be resized after changing the fasteners, but if they measure out the same when torqued then it's probably good enough.

Resizing has no impact on bearing size.

86LG4Bird

iTrader: (1)

I'd consider it more than just popular wisdom to resize the big ends when changing rod bolts!
If you're not going to resize them, then you're better off staying with the original bolts. The ARP bolts, when torqued per instructions, result in different load, ie. some deformation, in the cap and rod. That deformation is corrected by the rod hone process.
Doing things right is far more important than just replacing parts when building an engine.

Apeiron

If they measure the same when they're torqued down, then there's no difference in the deformation.

86LG4Bird

iTrader: (1)

I guess I'm making an assumption here that others are not: I can pretty much guarantee if he measures the rods right now, he's going to find the big ends out of round. THAT's the big limiter in the engine being able to handle decent power over 5000 rpm after the rebuild, more than the type of bolts used.
It's typical to see .001 to .0015 OOR in anything that's been driven "spiritedly".

Gsoleski

what's OOR? Out of round? This isn't going to see any strip time. Maybe once so I can try and beat my dad haha. But Should I measure the clearance now and then see what it is with the arp bolts? My local machine shop doesn't charge much to resize them so it may be a good idea

skirkland1980

iTrader: (2)

The arp rod bolts are such a tight fit that they distort the big hole. Make sure the bolts are installed before resizing. Or just take everything to a machine shop.

sofakingdom

iTrader: (1)

The act of changing the bolts distorts the hole. Doesn't matter what bolts are involved.

"Re-sizing" involves cutting a couple of .001"s off of the cap and the rod, pressing in the bolts, then re-boring the big end.

End result is, a rod that's a coupla .001"s shorter than it started out as, with a big end that's (hopefully) perfectly round, perfectly smooth at the transition from the cap to the rod, and the bore is perfectly perpendicular to the rod (a NOTORIOUS factory QC issue).

If you're changing the bolts, then for all practical purposes, it's necessary.

You'll find that by the time you buy bolts and then pay for all that, you could have bought NEW rods, FAR better than a bunch of old junk stock ones, for about the same money you have tied up in the old stock stuff. Except that instead of having nice NEW BETTER rods, you'll still have ... just .... stock.

Damon

When did resizing rods become "optional" regardless of whether the bolts are stock or have been changed out for aftermarket?

I haven't found a "seasoned" set of rods yet that didn't flip the needle all over the scale right out of the engine. They just don't stay "round" after tens of thousands of miles. Period.

Resizing the big ends of the rods is probably one of the most important operations you could ever do in a bottom end rebuild ranking only below boring and honing the cylinders properly.

Now here's something they DON'T tell you about new vs. old rods...... if you are resuing a seasoned set and resize the big end (after installed the new bolts, not before), it STAYS PUT after that. All the stress gets worked out of the metal from use in the engine and it will hold it's shape much more reliably reliably after that. Plus you know the bottom end balance is un-altered from stock.

Here's another thing they don't tell you..... not all aftermarket rods come with nice round big ends anyway. You always have to AT LEAST check them. If you find they need a resize (which is not at all uncommon), you might as well have done the operation to the stock rods and saved the cost.

I am not one of those people who says you should buy aftermarket rods at the drop of a hat because it's 2 cents cheaper up front to do so. In my own street builds I almost always resuse the stock rods, if they are original to the bottom end. When you're working on the cheap, keeping the bottom end a "matched set" has some significant advantages.

86LG4Bird

iTrader: (1)