most likely poor quality.
your best bet is to just use a good bolt and nut

 

Jeff, looks like you are using the "selftapping screws" the repro houses sell to go with these.

I found these not to thread smoothly into the well nuts, and they would not tighten up all the way.

I found some screws at the local Ace that looked exactly like the correct ones but are not self tapping. They would screw in nice and expand the well nut properly.

 

Thanks Jim.
Yes - these are the repros.

I will try a different screw. Thanks!!!

 

Jeff, the ones they sell at Lowes are exactly the same as from Rick's etc. The head markings are the same. I had to take my radiator out after initial installation and replaced the well nuts.

 

I had tried Home depot.
They had a bunch of them - but none the right size.
Will try Lowes - some had said a Boating hardware store.
I am sure they are much cheaper that way. Thanks

 

Jeff, the well nut kits from NPD already have the correct bolts supplied. The kit will run you $4.50 about the same if you buy the hardware separately at the store and providing you could find them. If you don't need them right away, buy the complete kit.

 

Has to be a quality issue.
Just installed 2 more repros that I had - one is good, the other "popped" in less than an hour.

Tightened the good one down VERY tight - I would bet - that one will last.

Going to stop by a hardware store - they should sell them for less than $1.00
Looks like these may be a regular maintenance item :clonk:
I am going to buy a box of them.

 

I bought a set of these from our sponsor. They have been on for months with no problems. Wish I had checked local hardware stores first though because shipping was not cheap considering the weight involved.

 

Found them for .90 cents each at a small hardware store.
Exactly the same as what I got from the parts guy.

I bought a box of them.

 

OK,,,,, sorry, I can't help it,,,, but unless you guys are 'total' restoration freaks or masochists, there is a better way. About 25 years ago I built a tray to hold the radiator. I copies 1970 or later GM products. It's really simple to do. I just took some pictures of it while the engine is out for its quarter century cleaning. (it might be back this weekend depending on the spark plug indexing) Anyway, I'll get those pictures online soon.
Edit: Here ya go: Any sheet-metal shop can bend this up for you.

This shot is of the passenger side. Note the rubber button to limit side-movement of the radiator.

 

OK,,,,, sorry, I can't help it,,,, but unless you guys are 'total' restoration freaks or masochists.

Yes - that is me.
They do seem to be holding now.
I tightened them down real tight.

 

I have found,if I want to remove the radiator, that the bolts will not come back out of the nut. The nut will spin inside the rubber. Last time I put antisieze on the bolt. Hopefully the bolts will come out next time without spinning

 

Fred - that is similar to the radiator installation of many other GM cars.
Many models used a "drop in" radiator instead of bolting it to the support.

Either way works well, but i really want to stay all original.

These well nuts are very common in the marine industry.

 

Fred - that is similar to the radiator installation of many other GM cars.
Many models used a "drop in" radiator instead of bolting it to the support.

Either way works well, but i really want to stay all original. As far as 'either way working well', that I would find issue with. That's the reason GM changed the next year. This method really isn't very good.

These well nuts are very common in the marine industry.

Cool Jeff. And that's where I got the idea. And as far as either method working well, that's where I disagree. The reason GM changed is because the method they used on our cars didn't work well. That's why this topic often comes up.

 

Can't argue with that.
The well nuts are just stupid.
GM used them for the voltage regulators in 67 too. :clonk:

But still, I like to keep it how it was...
Not how I wish it was.

 

and 68.

if one spins coming out, it takes about a second and ahalf with a cutoff wheel to fix it!

 

My biggest gripe with these damn nuts isn't getting them off. It's installing them. My original radiator was heavy. Took me forever to line them up. But I was only a child. Now the radiator just drops in.