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Heat treat questions

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John Loftus

John Loftus

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The threads on the gas tank hold down strap and seat frame pivot bolts had worn so I gas welded the damaged areas and then used a die to cut new threads (see images below). Should I heat treat the threads and if so what is the procedure? I recall heating things red hot and quenching in oil a few times back in junior high shop class but that was a few too many beers ago. /ubbthreads/images/graemlins/grin.gif

Cheers,
John
before.jpg
welded.jpg
after.jpg
 
I'm no expert, but it may well be that whatever you do, it won't make much difference. The welding rod you used is probably not even close to the same composition as the bolt. What you have left of the new material after cutting the threads is mighty small. If you got the bolts red hot to weld, then let air cool, that may be annealed enough to relieve brittleness. Oil quenching may induce unintended brittleness. The good news is that if you drive carefully enough, there will never be enough stress on those threads to test their strength.
 
If you were able to run a die over the welded areas they were relatively annealed as Cutlass suggested.

What caused the damage to the threads in the first place? Was it rust related or from fretting around in an oversized hole?

If you have an unmolested original bolt you can test it with a file to see if the originals were hardened. I doubt they were particularly hard but the file test would give you an indication if you need to do any heat treating or if you can use the repaired parts in their annealed state.
 
Yes, they were cherry red for welding and I let them cool slowly. The welding rod was soft because of the threading operation needed. I don't think the bolts were originally heat treated but just don't want to leave the bolts/threads weaker with the welding operation.

The gas tank strap bolts go through a hole in the boot floor (thin gage sheetmetal) and then use a washer and bolt to complete the assembly. The wear may have been from rust and/or the straps being loose and the tank moving up and down. There is a closed cell foam insulator under the tank and perhaps that gives the tank some wiggle room or collapses over time that adds up to wear over the years. The wear on the seat pivot bolts is easier to pin point. Everytime the seat back is moved or stressed the sheetmetal wears the stud a bit. Perhaps just using a small sleeve or bushing would be better than "heat treating" to reduce the wear on the threads in these areas.
 
Hi John,
Heat treating usually means hardening a material. First off, is the particular material heat treatable to begin with? Some low carbon steels are not.

In very general terms, heat treating consists of heating the material to a quite high temperature & controlled quenching to make it very hard. Next the material temper is "drawn" to a softer, less brittle state by heating to a lower temperature & quenching.

Successful heat treating requires knowing the exact material & it's requirements, carefully controlled heating & cooling. A garage attempt will likely leave the material either soft or hard & brittle. Provided that the specific material was even heat treatable in the first place. Annealing consists of heating quite hot & very slow cooling, to leave the material in it's softest state. If the bolts were heated to red during welding & allowed to cool slowly, they are likely in their annealed state & usable as is. Better too soft than too hard for these particular T bolts.
D
 
Hi Dave,

Thanks for the info. I will keep the T bolts as is and look for ways during assembly to protect them from movement and wear (and perhaps they just need careful assembly to accomplish that goal). Thank everyone for the comments!

/ubbthreads/images/graemlins/cheers.gif
John
 
Hi John,
These may be just what you’re looking for. They have a 5/16” I.D. and a 7/16” O.D. and about a ¼” of sleeve. Might need to use a uni-bit to widen the hole in the trunk floor a little. Finish it off with a nylock. If you can wait ‘til Friday, I’ll be in the neighborhood.
226260-CIMG0338.jpg
 
Just one minor point to Dave's comment on "drawing". The process is also referred to as tempering. After a part is quenched following heat treat (depending on the material) it is raised to another high (but lower) temperature and held there for a controlled time. From there it is allowed to cool slowly without a second quench. The purpose of this is to cause and control phase transformations inside the structure of the metal itself.

Almost all steels (excluding most, but not all, stainless steels) can be heat treated. On low carbon steels such as 1010 or 1018 the common process is to add carbon and nitrogen to the surface of the part and case harden it. Higher grades of steel go through heat treat processes that change the internal structure of the metal to harden the part. There are several types and methods of heat treating those materials and they are the ones that are often heat treated followed by tempering.
 
Greg,

Thanks for the offer but will most likely be in Los Angeles on Friday all day. Those sleeves may work out .. I also have similar pieces in nylon that might work too. At any rate, still need to top coat the tank and straps before installing. I have a feeling you will be 'in the neighborhood' often this summer /ubbthreads/images/graemlins/grin.gif

Cheers,
John
 
Problem with the sleeves is that the boot floor will not take up the depth of the sleeve. The nut will bottom out on the sleeve before the whole assembly is tight to the floor. This could be taken up with washer(s) around the sleeve, as it protrudes through the floor. But as I was trying to say earlier, this is a bit of a design goof. IMHO, the boot floor should be reinforced, as is the cockpit floor where the seatbelts are fastened.

Good education on heat treating, though. The real lesson is that heat treating is a vast science unto itself, and doesn't yield to the casual hobbyist easily.
 
Hi Cutlass,
My thought was to insert the sleeve from underneath and have the nut tighten up against the flat end. The sleeve would project up into the trunk area and wouldn’t interfere with anything due to the length of the T bolt.
 
Need to use STEEL Lock Nuts!! Especially by exhaust area!! /ubbthreads/images/graemlins/hammer.gif
/ubbthreads/images/graemlins/cheers.gif
Ed
 
Hi Ed,
I here what you are saying, but I would wonder if steel locknuts would damage John’s thread repair.
 
Good point Ed.

The Parts book shows the big D washer, lock washer and lock nut but the PO had used a thin nut (the 1/2 high ones) instead of a lock nut. This is most likely the cause of the straps getting loose and causing the wear on the T nut.

Cheers,
John
 
HI John, why not just put a short steel sleeve over the threads to ride in the boot floor hole."I" would then use a regular nut followed by jamb nut to lock everthing in place.---Keoke
 
I don't know Keoke. Putting that sleeve in there could be a slippery slope. Before long I'd be rigging up a fuel cell back there /ubbthreads/images/graemlins/grin.gif (oh wait a second .. that's what Greg would do!! /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif )

Seriously though .. it's a good idea. I'll wait to see how it assembles to see if I need a sleeve. Just had another idea. If one uses a thin nut on top of the boot floor and one underneath you could keep the T bolt from moving .. just depends if there is enough room for a nut on top when all is tightened down.

/ubbthreads/images/graemlins/cheers.gif
John
 
Hi John,
By now I'm wondering why the T bolts are moving around enough to wear anything. If the straps fit the tank & there is proper padding on straps & tank bottom, pulling the bolts down should put the bolts & straps under noticeable tension. If the tank is firmly located, I don't see why it is moving enough to wear the bolts.

As Doug said,
"What caused the damage to the threads in the first place? Was it rust related or from fretting around in an oversized hole?" My 50 year old straps & bolts show no signs of this strange wear.
D
 
Dave, I think that it is just rust damage. Mine had the same skinny section as in the picture about where the washer sat below the hole in the boot floor. It looked like rust damage to me. The bottom of my gas tank had rusted through with many pin holes. I believe the root cause of this was a leaking boot lid fit/seal so a little water would get in and do it's work to the lowest parts in the boot, ( tank hold down t bolts and bottom of the gas tank ). John, If you have not inspected your gas tank yet, take a wire brush to any rusty looking areas like you are going to clean them up to paint the tank and check for pin holes in the bottom
of your tank.
 
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