If the bolt that came off my car is in good shape I am pretty good at wire wheeling it and giving it a shot of paint... I am talking about a bolt in good shape, not one thats rusted partly away or worn in half....
What is everyone's thought about the possible fatigue these 40+_ year old bolts might have.... My reason for posting this is my lower control arm bolts on my 85 parts I am putting on my restomod frame....... They have to take alot of abuse for 40 years....
Any thoughts on here about this??

 

I think the risk is lower for original old parts, than for new ones....I reuse bolts whenever I can

 

If it's not rusty and the threads are not stretched I would use them. After the car is done check them after a few hundred miles. If they still are tight you're good. If not easy enough to replace

 

N M how would you know if bolt threads are stretched or not. if the bolts look like crap and are wore out then replace

 

start the bolt on a thread chaser/ die and see if there is anyc
play as you tighten it.

 

Bolts can fail in two directions: shear and tensile failures.

Shear is due to the fastened parts sliding perpendicular to the bolt. If a bolt is properly torqued to hold the two parts from sliding, there is little chance of bolt failure by shear. If the bolt holds a rubber bushing, the rubber takes the movement and it will fail before applying the shear to the bolt.
Tensile failure is due to exceeding the elastic limits or yield of the bolt. If the bolt was originally torqued to yield, it should be replaced every time as is the case with many new car head bolts. There are no bolts on a GM vehicle of the 50s, 60s, 70s, or 80s that I am aware of that the bolt torque takes the bolt to yield.
Thus, I know of no reason any bolt used in automotive applications up thru the 80s should not be reused, even rod bolts, head bolts, main cap bolts, etc. I have reused bolts in automotive applications for 50 years with no failures.
You can identify those bolts that should be replaced when the manual requires it to be torqued to an extremely high torque value and then turned an additional number of degrees. This indicates the bolt is taken to maximum bolt stretch just prior to yield.
In structural steel applications, most bolts are tighten to near the yield point to achieve maximum clamping force of the two parts. Most of those bolts are either A-325 or A-490 (Grade 5 or Grade 8) bolts and are discarded if replacement is needed.

 

I tend to agree. Low volume lots of specialty fasteners are usually made offshore, where manufacturers tend to lack the rigid control of steel metallurgy and heat treatment seen in original GM parts. Using recently made parts is therefore a crapshoot, at best. The new ones will also usually have the head markings of an extinct manufacturer, so no traceability, no quality guarantees.

Use the originals, if they are badly fatigued, they won’t survive the tightening process to a production torque spec. Don’t clean them with acid, though.

 

I start the fastener by hand and if shows no resistance, I call it good and move on.

 

I agree with reusing. Worked at a nuclear power plant and we reused fasteners all the time. Reactor vessel head studs were stretched hydraulically to achieve the specific length , then the nuts were run down by hand and the hydraulic stretching tool relaxed, then another measurement to verify proper elongation. On the opposite end of the reactor control rod drive mechanisms were fastened by 8 socket head cap screws that were torqued either hydraulically or with a torque wrench. Not necessary to replace unless suspected of some type of damage. Many other critical fasteners are reused regularly.

Drive em safe
Leo

 

A couple of notes on the previous comments:
1. Tightening to yield can only be done with electronic monitoring of the tightening process, where the tightening is immediately stopped (electronically) when joint yield is detected - using torque vs angle, or torque vs tension feedback. During such tightening, the moment the torsional load from the wrench is removed, the load on the bolt again drops below its yield point, with only imperceptible permanent deformation. As such you don’t need to replace a bolt that has been tightened to yield.
2, Tightening to yield cannot be done to any specification by hand. The process described previously, where the bolt is tightened to a a given torque, followed by an additional rotation of some number of degrees, does not accomplish tightening to yield , it is done just to get a more consistent stretch of the bolt, before it actually yields.
3. In any case, no bolt on C1 or C2 Corvettes was deliberately tightened to yield at the assembly plants, so I wouldn’t worry about that.
4. Very experience mechanics can and do tighten to yield every day, as the feeling of a subtle “give” of the fastener at end of tightening is, in fact, feeling that “yield”.

 

Vettrocious, Have you never used a stretch gauge on rod bolts ? I do and it's recommended on HP engines.

 

Back a half century ago, working on nuclear construction, a vendor provided a batch of foreign made structural bolting. Each batch of bolting was tested using a strain gauge to determine clamping force as well as a stretch gauge to determine the yield point. The lab found the bolting from across the pond constantly failed prior to meeting the acceptance criteria for structural bolting even though the CMTRs stated it had been tested and met the ASTM requirements. Thus, the NRC determined only bolting made in the USA would be used.
Go figure.
Of course we don't have all of the equipment to test bolting, so I put my faith in GM.

 

They lasted 60+ years already....

 

Actually these lasted 40.. As I said above they are from my 85 suspension parts going on my restomod frame for my 65 body...

 

Is it OK to re-use any of the drive shaft U bolts if they are in good condition? I have read here in the past that they should not be re-used. Thanks all Big-K

 

The connecting rod bolt is the most stressed bolt on any engine. It's critical point is the top of the exhaust stroke, blowing down. All good rod manufacturers recommend measuring the elasticity of bolt by stretch based off the metallurgy of both the bolt make up and connecting rod. All good rods will have a weight card indicating the stretch amount and APPROXIMATE torque to achieve this. For example the ARP 2000 bolts in a Callies Compstar rod for an SBC need .0045-.0055" stretch. Some take 75 ftlbs, some take 80 or more. My connecting rod bolts are all recorded, so at refresh I can tell which ones are not to spec. A stretch gauge is very important in professional engine building.

Brandon Unklesbay
All-In Performance, LLC