Threaded rod through a sheet metal hole vs a non-threaded pin -- are the threads going to cause problems?

[Tommy2Tone]

I made a hood scoop and am attaching it to the hood using screws that originate in the underside of the scoop and then go through holes in the hood skin and the hood understructure. Similar to how the scoops were put on some of those Roadrunners and the like back in the late '60s.

Should I fabricate some kind of pin such that the part that is touching/going through the hood skin is not threaded? Does it make a difference over time? I recall once seeing something about this but I cannot place it. Thank you.

(ignore the rust in the photo -- it looks like **** from being at the beach and is inevitable but that will all be cleaned off and treated before finishing.)

 

[RoninB4]

Do you have the capability of making the custom non-threaded pins? To me, a threaded shank in a sheet metal hole will act like a file up to a point and can/will damage at point of contact due to vibration. You can create bushings for the fasteners to go through that can reduce the "filing" action.

You can create the custom pins with a non-threaded shank so vibration will just slide on the shank.

You can also create/use the custom pins and bushings to provide as much contact area as you want. You'll have a choice of materials and can make one or the other a replaceable wear component instead of wearing away an enlarged hole in the sheet metal. Small Delrin/UHMW bushings (or rubber grommets that cut down on noise and are commercially available) should be cheap, easy to make, and save the expensive sheet metal.

A thin film of grease on the non-threaded (and polished) shank of the custom pins will provide lubricity. Just a suggestion, would like to see photos of what you decide to do.

 

[joe49]

...or you could use quality fasteners and torque them properly.

 

[BD1]

What about plug welding threaded studs to the scoop ?

 

[Tommy2Tone]

In essence that is what I did...welded nuts to the inside of the scoop then will attach with screws and some loctite. I think I will just go with threaded rod and if tightened fully it will not move. I could fabricate some kind of stud with a narrow plain section and threads on both ends but I am not sure I could get the width of the plain section to be correct and not interfere in tightening the nuts...we are talking .035 thickness material.