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I recently mounted my Jab 3300 on my CH750. The mount uses 4 AN-6 bolts and 2 AN-4 bolts to secure it to the firewall. AN-363 (metal locknuts) are used. It's been my experience that metal locknuts require a little more "oomph" to wrench than do the usual fiber locknuts. Does this affect the torque values? I've looked at the FAA torque tables and they don't mention AN 363 nuts (or I missed it! LOL!). Also, different values are given for AN-364 and AN-365 nuts used in tension and shear. Looks like an engine mount is in both tension and shear?
Anyone know the correction or actual torque ranges for AN-4 and AN-6 bolts with AN-363 metal locknuts?
I own torque wrenches and find in my mind they are a lot to do about nothing, but there has to be a standard to be guided by. Eaa has some videos on this subject perhaps a message to them would give you an answer. For years I have used the practice of a 90* turn past the first resistance using a normal length wrench handle. As I interpret that the lock nuts are to replace lock washers, I could always observe when the lock washers were flat, tight enough!!!! Then again how do you know the torque wrench is calibrated. Check the EAA Buiders Hints videos and the values in the Zenith builders guide.
I think I missed the point. I would add the torque to turn the locknuts to the torque values Sorry
Thanks to all for the good info!
Caleb replied this a.m. that for the metal 363 nuts, use the 365 torque tables (as found in AC43.13-1B) for the bolts. He did not specifically mention, but as pointed out by others above, one would determine the drag torque of the nut and add that to the value.
It seems my concern about the metal locknuts was "much ado about nothing"! It seemed to me that there was an awful lot of drag when using the metal locknuts, so that's why I was concerned about the torque values ... I think the engine mount is probably one of the places where proper torque is a good thing!
However, I found that although initially the drag is high, once you get the nut going on the threads, the drag drops off considerably. With AN 6 bolts, the drag torque on the metal nut was only about 2 ft lbs. - Sooo, looks to me like just torquing to mid range gets you safely within specs.
What about castle nuts and cotter pin. Might be a worry free alternative.
I think using a castle nut on a motor mount would cause a lot of worry! LOL! I would think you need that mount defintely torqued-down so there is no possibility of motion where it meets the firewall which would result in fretting. I don't think castle nuts are intended to be used where there is a significant element of tension in the bolt - they are more or less just retainers for a bolt in shear on a rotating part like a control linkage.
Torque wrenches are a great tool for getting consistent values but accurate calibration should not be taken for granted.
When I bolt things together my real peace of mind is Loct-Tite. Get the red stuff. The blue stuff doesn't hold like the red. Be careful not to get carried away on the smaller fasteners like AN-3 caps and nuts as the threads will often be damaged during dis-assembly.
Speaking of dis-assembly, warm up the nut to about 150 Farenheit with small propane torch on nuts to get easy release if necessary.