Hey guys, I ran across something once that made me wonder. A friend of mine told me to torque the tension bolts of 13B's past the torque spec of 27-29ft/lbs. He made the claim that apparently it holds together better. I'm not sure if I buy it or not and I wanted to get some opinions on it, please.



B

 

yah if we are building a motor thats gonna get beat or has tired housings in it we go to like 35, i dunno if it makes a difference its not like they die from loose tension bolts



mike

 

It might keep you from a coolant leak but you risk breaking the tension bolt so why bother , i don't know.

Try it and see if the bolt snaps.

 

If that's the case then there would be no torque spec requirements, it's just do it up as hard as posible

 

I always go about 5-10 foot pounds beyond recommended torque to make up for friction in the threads and bolt head.

 

wouldnt you think the engineers coming up with the torque specs are taking friction into account when writing them up? At least a nominal amount.

 

Come on man, are you really asking me that? Engineers do not turn wrenches and do not design torque specs for corroded and old parts. There is a big difference between fresh threads with clean, exposed metal and aged parts having been assembled for a number of years, exposed to heat, grease, dirt, and water. Sure, I could lube down my threads and seating faces to recover the low coefficient of friction that they once had, but not if I am going to have Loctite on them, which I always use on critical fasteners.



Think like the pilot staring at the ground thousands of feet below, as his lift strut Jesus bolts start to work loose . . . I guess my aviation backround makes my outlook a little bit different than most.

 

oh, well I always chase through threads in critical areas to avoid that problem, especially the tension bolts and respective holes.

 

I think the main reason for giving a torque spec is so you get even pressure on all bolts. Thats much more important than the actual torque figure.



Gary

 

torque specs are for clean dry bolts. The bolt needs to be stretched into it's working range. Like a spring, but not too far. Pull it too far and it isn't a spring anymore. It may become two pieces.



If you lubricate the threads and under the head and under the washer, and then use the dry thread torque figure, you have already over torqued the bolt.



In the case of case bolts (pun) they are so long that they have a big working range, and there is some latitude on torque that can be used. If you get to close to the top end of the working range, the engine will grow a bit with heat and over stretch a bolt. It may not break, but will not return to the correct tension during the next heat cycle. The over torqued bolt is now (undertorqued). Racing Beat has a list of overtorques to use for different end uses.



The bolts ring like bells, or more likely, guitar strings, in sympathy to the harmonics of engine RPM. The race bolts have a rubber sleeve molded onto the center of the bolt to prevent that. You can just slather on a spiral bead of silicone and do the same thing. The ringing bolt tends to break off right at the front iron in the threaded area. Picture is a 20B for aircraft use.



Lynn E. Hanover