If the bolt has experienced permanent deformation, it should be longer than a new bolt. If it has only experienced elastic deformation, it should be the same length, and good to re-use.

 

Every bolt is a different length...

 

Sorry I'm having a bit of brain fog today; I mean, if you have a new bolt and a used bolt, you both torque em down to the same torque, if the used one has experienced permanent deformation the percentage of stretch it experiences should be more than the new bolt(?). Use one of those rod bolt micrometers to check.

 

You need to know the length of said bolt prior to torqueing them or prior to plastic deformation.

 

Well, guess I'll have to bite the bullet and get the stock bolts

 

To elaborate on Y2K's post and for general info, dos centavos on elastic vs plastic stretching.

Put stress on some steel and it will stretch a tiny bit relative to the strain. As long (heh) as it returns to original dimension that is elastic deformation. That can be repeated forever and will not degrade strength of the part. Every steel casting and stamping you depend on in your truck is engineered with this strength in mind.

Once the steel "yields" aka deforms plastically, it stretches permanently and will not return to original length. Your tie rod is bent. He's dead Jim.

Dead for re-use except for the Hades-bound beancounters that wanted to take advantage of the available strength at the top of the graph labelled "strain hardening". The steel hardens as it stretches and can support greater tensile loads. TTY bolts were born. Sure save .7257 cents per unit by using a smaller bolt that must be torqued precisely and can only be used once. Maybe there are valid considerations I am unaware of, but I'm pretty enamored with the idea TTY is the work of the devil.

Back in my lab days in the steel foundry doing QC I pulled a lot of tensile bars per ASTM. Yield strength, tensile strength, and diameter pre and post failure. Gives you a really, really good idea how any part made from that steel would behave under stress.

 

It has always been my unguided opinion that TTY bolts provide a more consistent clamping force in a production setting. Seems head, rod, and main bolts are the common TTY and would also be most critical to have even distribution of clamping. Another factor may be they are less likely too loosen during use.

 

That is the key consideration right there. When ~85% of the torque is used to overcome friction and said friction varies wildly with lubricant used, other methods had to be used to get to even clamping. Can you imagine the gauge R&R that had to be conducted for that?

 

Not for a 7.3 but I remember from my supervisor’s toolbox at my last job he had a bolt gauge. It was for one specific bolt on either a big Cummins or old Mack engine. It might have been for the head bolts, they required a lot of torque.

 

People been reusing these rod bolts for ever in these engines. Never heard of a problem. Rod breakage,due to tuning on these engines but not bolts. Now if you are building a runner, high HP, then I'd change them. That's my 2 cents. Just read this whole thing, am now following. Good luck, and take pictures if you can. Oh, I thought I saw a bad spot on the cam, but it was really hard to see so not really sure. It was still in the engine at one point.

 

Seems that main bearing cap studs/bolts are also unobtanium right now. I can source some grade 10.9 or better yet 12.9 bolts of appropriate size to use, but then what to do about the oil pickup bolt? Welding a small stud on to the end of a standard bolt would mess up the heat treatment.

 

No wurries. Gotcha covered. Girdle up. Comes with bolts (studs).

 

At the risk of derailing a bit, what would you do for an oil pan if using that girdle?

I thought I saw the main stud kit available at every place I looked, I’m rebuilding mine too so the bad news about the rod bolts sucks to find out.

 

You don’t. Running a girdle like that means you are running in Super Stock Diesel Four Wheel Drive Trucks at the tractor pulls and you should dry sump it for when you pop a wheelie.

 

Use the rod bolts. I would worry more if I put in a bolt not made for that job only! But to each there own I guess.