Changing rod bolts

[Robert Swartz]

Just a question here. I have a SBC bracket motor. It is in pieces. It is a good assembly, small journal steel crank, Speed Pro pistons, balanced, a lot of work done. When I got the rods out, they are a set of reworked stock steel rods, a couple of the nuts for the rod bolts are missing. I'm contemplating just replacing the rod bolts altogether with a new set. Not being a machinist, can I just pound out the old bolts and replace them with new ones? I deal with reman engines all day long and if we need to replace rod bolts, that is all we do. Am I being too simplistic with this? I don't see a need to have the rods reworked just over the bolts.

Any advise is appreciated,

Robert Swartz

[Robert Swartz]

Originally Posted by Pete Muenzer

Robert, this has always been an interesting topic. I have always been told whenever changing rod bolts the rods must be resized. I have always been afraid to ask this question because I am not a professional engine builder and do take the advice of those on here because they have much more knowledge on this than I ever could possibly learn. My question is, Is it possible to clamp the rod on the crankshaft, torque it down to spec then change one bolt at a time using the crank as a mandrel to keep the rod end in shape? I read this method in an old engine building book I have on Big Block Chevys. Also when changing rod bolts that have dowels and cap screws instead of bolts is it still necessary to get them resized? All of these are just questions from a novice so don't be too hard on me.

Pete,

I'm not a professional engine builder myself. I put reman diesel engines together everyday but they're a different animal. Yes, the resizing issue is what I'm concerned about. These rods already have aftermarket bolts in them. I have a high end circle track shop down the road from where I work. I may just take one of the rods over there and see if they can come up with some suitable replacement nuts. That would alleviate changing out the bolts and potentially having to rework the rods. I'm pretty sure I'm not the first person that has ever lost a rod nut or two, LOL!

As far as being afraid to ask a question. Here's my take. There are a lot of things I know. There are also a lot of things I don't. There are only a couple real ways you learn, either by asking those more knowledgable than yourself, then taking that information and do your own research to verify if it is indeed good. Or do something and observe the results, sometimes that works, other times it doesn't. When it comes to cars, you got to be "not afraid" to ask questions.

Robert Swartz

[BillK]

Robert,

I would just get a set of ARP nuts and go with that. I know guys that have replaced them one at a time, and not had problems, but I sure dont like doing it. The other issue you will have is unless you know exactly who's bolts they are, what do you torque them to ?? Or stretch ?? If you are lucky enough that they are marked on the top (ARP etc) you can get the torque specs, but otherwise you are just guessing. It is pretty amazing at how much difference there can be from manufacturer to manufacturer.

Either way, it would probably be a real good idea to have your machine shop put them on thier rod gauge and see how round they are after you torque them.

[Bob Pagano]

Have them checked after you change the bolts, one bad rod could cost you an engine.

[Adger Smith]

Don't pound them out, just repalce the nuts that are missing. In the 40+ years I've been doing machine work I've seen many bearing failures vs bolt failures. Replacing bolts without checking or resizing can cause failure, bearing failure. The center will change on the bolt by a little and shift the cap if you replace the bolts without resizing. ARP recomends you resize when you replace bolts. It is in the directions you receive when you buy their bolts. OH, thats right guys (we) don't read directions. :~) You are dealing with very small numbers on rod roundness and size. It can get nasty quick.

[Robert Swartz]

Thank you for all the response. This does give me some thoughts to ponder. I didn't want to over simplify this. Getting the big end of the rod out of round and bolt stretch were my two main concerns. I am going to look into possibly just changing the nuts out with new ARP's. The engine has to go back to the machine shop for other work, might just be cheap insurance to take the rods and have them redone.

Robert Swartz