Weld Filling Body Mount Holes

[Rick Iverson]

Gents;

I have broached the filling of pan mounting holes on the chassis bottom before, and was well advised by Steve Lathrop it would be a recipe for disaster. Presumably, because the holes are two to three inches apart, and there are about a million of them.

But I would like to fill the coach mounting holes on the chassis lower sides rails. Most are 8”-10” apart, a few are 3”-4” apart. Hole sizes are ~0.30”.

Thoughts on this, please?

[steve zemke]

Pictures?

[ChristopherBernard]

If you are welding the holes up you will get shrinkage when they cool. The more heat you input, the more shrinkage you'll get.
More and larger holes= more shrinkage. This could result in a wonky chassis. If you can lock the chassis down to an inflexible (relatively) fixture you can possibly reduce the effect and track any deviation from straight.
Brazing may require less heat. Technique, speed and accuracy will also affect your outcome.

[BeerBudgetRacing]

What is in the holes now?

When I rebuilt a few years ago i replaced damaged rivnuts with slightly bigger ones with floating nuts.
Worked great for fastening bodywork.

https://www.mcmaster.com/riv-float-nuts

[10rmotor]

If you're gonna fill the holes with weld material, I'd suggest using a mig welder. I think you'll get the least amount of heat input. Bolting down or restraining the structure while you weld it, imo, won't really help because it won't prevent the heat stresses. As soon as you unbolt it it will do what it wants.

If you don't have a mig and are going to tig it, maybe use silicon bronze filler as its a bit softer and not as much heat is required.

[azjc]

I use Silicon Bronze with a TIG welder - less heat, you "lay it on" like gas brazing.

[innerloop]

Rick,

Could you first insert a metal rod of the appropriate diameter to fill the hole and then weld in the rod to use less weld and less heat?

[Rick Iverson]

Rick,

Could you first insert a metal rod of the appropriate diameter to fill the hole and then weld in the rod to use less weld and less heat?

Alan, excellent idea.

[Bob Wright]

I guess one of the underlying questions is why do you feel you need to plug those holes? It sounds like there aren't that many of them and I suspect they won't affect the structure too much (the belly pan is much more important). When I rebuilt a PRS, I utilized some of the available holes with nutcerts and ignored the rest of them when attaching the bodywork.