When I tore my engine down for rebuild (75 L48), I made sure to stamp the cylinder number on the end of each rod. I was hoping a good honing was all that would be needed and hoped to reuse the pistons.



My block needed to be bored, so I purchased flat top pistons to hopefully up the compression a little. I had shown the machinist that the rods had been stamped and he acknowledged it. When I got the new pistons/old rods back, 6 of the 8 had the dot on the piston facing rearward when placed in the as-marked location, being careful to make sure the chamfer pointed toward the fillet (I think that’s what it is called) on the crank. I called and brought them back up to him to show him, and he says that they don’t pay any attention to rod markings as they don’t know if they were marked properly. I told him it bothered me and he agreed to turn the pistons around. Then he claimed he couldn’t do it because the pistons would break if he removed the wrist pin. He gave them back to me with his markings (in paint pen) on the rods indicating the new order.



I have examined them and they should work as he laid them out, but questioned why they didn’t just follow the numbers on the rods. After complaining about a “bunch of Youtube amateurs” and various other derogatory terms for the inexperienced, he told me you should NOT put the rods back in the same hole they came from, and that it’s recommended practice by some engine building association to switch them up.



My question is, is he telling the truth about NOT putting the rods back on the same journal they came from? Should I use them as he laid them out, of find a different machine shop?

Thanks in advance for any insight.

 

Oups!

This is correct in the sense that sometimes the rods are marked on the "wrong" side, but usually it'll be the whole set, if not then one suspects a mixed set of rods which brings additional concerns into the mix, so I wouldn't say they should be ignored.

This can be a problem as the "press-pin" system does not include any concern for the piston survivability in the process of removal.

So now "if" there had been any effort in specific piston to bore matching in the original endeavor, what you we have now?

I can't remember that "recommended practice" ever being made by any truly capable group, this as associated with these engine examples anyway; but it sure sounds good! Maybe from a rebuilders' point of view all the rods are the same (should be) so it doesn't matter if you mix them up, and that I suppose one can't really argue.

From here, all I can say is that if your not comfortable carry them to another shop and have them look over what has been done and advise you.

Scott.

 

I usually dont bother with using connecting rods in the same holes if the pistons are new and the cylinders honed...It would only matter to me if they werent new, balanced and resized. The only thing that really matter is that the sets are correct ( Rod and Cap ) and the main bearings caps are in the correct place. If the machinist marked them for a specific position, do it. Everything is balanced correct? You got the crank polished to correct?

 

And this is how confusion unfolds in the far future.
10, 15, 20 yrs from now, on a forum:

I just bought a C3, dropped the pan and noticed not one "marked" rod was in the proper bore.
Did it come this way from the factory?
Or, the P.O. must have been drunk. What should I do about . . . . . . .

 

rods arent marked for bores unless its just to replace rings so I dont understand why people bother, but again I work with a guy that is OCD and he is all over the place with what is important to his OCD and what he doesnt care about...strange affliction to me

 

I don't know, I'm extremely **** about putting things back exactly as they came apart. Were these rods resized? Was the crank polished? If not. Then absolutely no I would not mix them up.
Once I installed one piston on a rod backwards. I pressed the pin back out. Turned it around and pressed it back in. That engine is still running fine.
Properly supported pressing the pin out should not damage the piston. But Properly supported is the key.
The shape of some pistons makes supporting them properly difficult. Others, no issues.

 

Rods don't care where they came from as long as they go on in the right direction against the crank radius.

If they resized the rods...it doesn't matter if the caps were mixed up...though I agree...it's not "cool" to not pay attention to it on a customer's engine. If they weren't resized..they will need to be done now.

With the proper rod press...they can be removed and installed in the correct position without hurting the piston. There's no pressure on the piston at all with the correct tools.

Not sure what pistons you have and what the valve pockets look like....but just remember the order of valves on a SBC is a little different with the two center exhaust ports side by side. Some pistons have different sized valve pockets designed to clear a large intake and a smaller exhaust. But most have "generic" pockets that will handle any application.

JIM

 

Not "always"!

Scott.

 

The hope was just to go with rings and bearings at the start.

 

Me too, I'm a CPA (CA down under). Rods were not resized nor was the crank polished that I'm aware of.

To be clear, I'm not saying the caps were not kept matched to their respective rods, just that they rod/cap combo was mixed around.

 

Always with the right tools and skill.

JIM

 

Are your piston pins offset? Then it matters. Many pistons are made that way. Otherwise it's not an issue.

 

After over four decades in the automotive machine shop business I would say the correct statement would be: "often" with the right tools and skill; but apparently you haven't experienced as many different application instances as I have, as sometimes, like it or not, there is no room for tooling (and I have a lot of this) other than that which does cause load to be applied directly to the piston.

And then, particularly for assemblies that have been together for lengthy periods, when you push the pin in the process of disassembly there may be a certain sum of shared material from the rod I.D. and/or the pin O.D. that will drag and score the pin surface, this then being pushed through the pistons' pin bore also causing damage here.

Scott.

 

ok

jim