I read on another forum about a guy who over torqued his 3/8 rod bolts to 60-65! Rec 50ftlb. Are the rod bolts trash now?

When I do mine should I buy a new torque wrench to assure accuracy? My wrench is about 20yrs old!

Thanks
Len

 

Rod bolt strecth is the prefered method of measuring the torque on rod bolts and the torque measure at the nut can vary on two bolts tightened to the saem bolt stretch. But ARP did a study on apply their assembly lube to rod bolts and tightening them 3 times where they found the bolt to be stretched to within .0005 inches of the correct stretch 99% of the time. Pretty good for street use, check it out:

http://www.chevyhiperformance.com/ed...=text&id=49258

 

They aren't trash if they are over-torqued but they shouldn't be run that way. They will be more prone to failure at that torque setting so they should be re-torqued to the recommended value. The correct torque is very important for the life of the fastener. It is based on the ulimate strength of the bolt. If the recommended torque is exceeded the strength of the fastener isn't increased. In fact it's working strength is decreased.

As for getting a new torque wrench, if it is a good quality "click'- type wrench just have it calibrated. It's better to recalibrate a good wrench for $30 rather than buy a cheap $30 wrench.

 

From all that I've read, it's the rod bolts that are usually the cause of engine failure. By over torqueing the bolts, I'd assume that the bolts are over stretched woud could fatigue the life of that bolt.

Another thing is the intended use of the engine. If it's going to be a car not often driven, & never going to be spun to 5000+ rpms, then maybe it'll be fine. If the engine is going to be ran though it's paces, then I would replace the bolts (cheap insure considering the cost of a blown engine ;) ).

 

Thanks. I'll pay extra attention when I get to that point.

I've been using the old "beam" type torque wrench. Can those be calibrated too??

 

Don't use those things on something as critical as rod bolts. Borrow one from a friend or rent one from the neighborhood parts store.

In my opinion, rod bolts are THE MOST CRITICAL bolts of the entire engine. If you think about what that crank and rod are doing -- upwards of 6000 RPM and that crank trying to change direction of that rod by pushing and pulling. What other part of your engine has that much strain to put up with ?

Don't skimp on bolts, use a good torque wrench. Make sure to oil the bolts on the threads and under the heads when torquing.

 

When you over torque a fastener you exceed it's elastic limit , it is trash ! Rod bolts are a critical fastener in the reciprocating assembly and one that should not be taken lightly . Just consider the ramifications should one fail . That alone makes the price of a set of rod bolts pretty cheap.

Happy Holidays

geo :steering: :iagree:


[Modified by ram82fire, 10:03 AM 12/23/2002]

 

I would get some 7/16" bolts.....

How is the project coming?

Bob :cheers:

 

Naw, I'm not the one who over-torqued the rod bolts. I saw a question on another forum & wanted some opinions here. I'm not that far along yet.

Project was put on hold for lack of time Bob. After Christmas I plan to resume assembly. I'd like to get the BB dropped around April-May 2003. I'm ready to put the crank in along with the rear seal & oil pump. I'm glad I posted this question, now I'll know not to over-torque the rod bolts. I think I'll invest in a new torque wrench too.

:smash: :smash:

 

Quote..Don't use those things on something as critical as rod bolts. Borrow one from a friend or rent one from the neighborhood parts store


Actually the beam type is very accurate and never goes out of calibration. It is just a matter of a careful eye and a little finnesse' A cheap or abused click type is the one that cannot be trusted. Most auto parts store never calibrate their tools. When "Bubba" drops a torque wrench it is imparitive to get it calibrated...I 'd bet that "Bubba" just brings it back and says nothing. Ask the counter guy when the torque wrench was last calibrated. He may not even know what you are talking about. Buy a new good one or stick with you old beam torque wrench. :cool:

 

That statement is not totally correct. Just because you over torque a fastener doesn't mean it has exceeded its elastic limit yet. It possibly could have. If it has exceeded its elastic limit, yes it is junk but I think a 15 ft-lbs over torque would NOT put the bolt past its elastic limit( if it does its a pretty crappy bolt). Chances are you'll have rod bearing problems from unusual wear patterns to a spun bearing.

 

Over-torqued fasteners have been 'yielded', and are not reusable as they will not return to their original shape once the load is removed (within 0.2%). Some fasteners are designed to be torqued-to-yield, because for most linear elastic materials, a jump in UTS is can be achieved in this zone of plastic deformation. However, this is not the case for connecting rod bolts. These fasteners are designed to 'preload'; i.e. keep the cap in contact with the rod as the assembly sees the severe tension at TCD of max rpm. If the rod and cap were to separate just a few microns, the bearing clearance will increase by a large factor and the hydrostatic film would not support the load, resulting in bearing-journal contact, and failure. Bolt strain or ‘stretch’ is the most accurate method to measure this preload. Fortunately, the connecting rod bolt permits this. A standard torque reading from a bolt head must account for thread and head friction, and bolt and rod material properties, which can lead a wide range of values. Connecting rod bolt tension is very important because the range of values is small. The bolt must be just tight enough to prevent separation, but not too high so that the bolt will not fatigue when the inertial load is added to the preload.


[Modified by Turbo-Jet, 3:10 AM 12/24/2002]

 

What he said :crazy: :iagree:

Hay SmokedTires!! I must say every time I see your sig, I wet myself!! :seeya

 

1970,

Sounds good. Take your time with the assembly. I was too afraid to assemble it myself, so I am giving you alot of credit (and to Bence) for giving it a try.

I have a '87 350 here at the house that I will try and put together in the future.

Bob :cheers: