The Stovebolt Site Forums The Shop Area General Truck Talk Frame crack repair?

Don't want to hijack Colin's topic but I have a related question on frame welding. My 1950 3100 frame has a couple small hairline cracks a bit behind the front passenger cab mount.
My plan was to clean the area then use penetrating dye to better show where the cracks are. To repair it I would drill a small hole at the end of the crack and have a friend who is a pro welder MIG the crack and then weld fishplates on the inside of the frame rail.
Is this a safe repair technique?
Thanks,
Bob

I repaired a frame that was literally ready for the front suspension to fall of. It was a 196? and the flanges had been cut with a torch for header clearance, then preceded to crack almost completely from top to bottom.

I ground the crack out completely, from both sides till them meet in the middle.
Then TIG welded the crack back together from both sides.
Dressed the welds flat, and also replaced the missing (torched) parts, welding the same way.
When done you could not tell it had ever been torched, cracked, or repaired.

Now that it is back on the road the welds have been inspected several now, no problems.

I would not MIG weld a frame, as it tends to create hard spots that can lead to more cracks. The weld is very hot, but the material around it stays relatively cold during welding.
TIG welding is a "softer" approach to welding, not as harsh as MIG welding because the heat is more gradually applied/ more time to soak in, so no hot/cold areas for stress cracks to form.

MIG welding may work for a while, but chances of failure down the line are greater, don't take that chance, TIG weld it.

Grigg

MIG welding a frame is just fine.

The difference between MIG and TIG (without getting into too much) is the weld puddle control you get with TIG. Weld penetration is achieved with the amount of amps used in the process.

Bob, I think your process is fine and will fix the problem at hand.

HC

Bob,
I checked with a few of the welders here who are older than dirt and they say the most important thing for success is slow cooling by wrapping it in an asbestos blanket. Let me know if you want to borrow a couple for a weekend.

Curt

I agree.Hairline cracks, especially in an area such as you're describing where there is little frame stress, are repairable.Just make sure you remove any rust or finish to shiny metal on both sides of the frame beyond the spots where you are welding.

Thanks Curt, It won't be anytime soon but I probably will take you up on that. Either I have bad luck or that is a weak area on these trucks as my previous frame had a far worse crack in the same spot.
Bob

I'm confused... why all the concern over welding a frame? Are they heat treated, made from some exotic steel that stress cracks if you use the wrong filler rod?

I TIG and Electron Beam welded aircraft engine parts for 5 years and TIG welded car parts for 5 years prior to that. If something is heat treated, you anneal it first and then weld it and then heat treat it again. If you're concerned about stress cracking you pre-heat the area before welding... if it's steel it can be welded.

I can see if you don't know a good weld from a bad weld where you could get into trouble. But if you can weld it with a wire welder it can't be that fussy.

How bout gas welding? Will that work as well?

We have done a MIG repair job to a hairline crack in the same area on a '54 1/32 ton pick-up. We used a powerful MIG welder and adjusted for full penetration. We supported the frame as close as we could to the crack and then cleaned the crack and then welded. We let it cool on its own. So far so good.

It seems likely that this might a area of considerable stress (or at least enough stress to cause cracks in the same area on a few trucks).

I think the main thing here is penetration. Grind out the crack in a nice "V" to acheive this. Right now you have lots of contaminents in the hairline crack, and that will cause a bad weld. If you "V" it out you can lay 2 or 3 nice beads in the joint to produce a stronger weld.

I like the idea of drilling a hole at each end of the crack. This works, I know. I would drill about a 1/8 or 3/16 hole at each end.

Awhile ago on "Trucks", they shortened a '66 long-bed frame. They sectioned the frame (which is not the same as repairing a crack) they "V"ed the outside of the joint, MIG welded from the inside, then filled the "V" on the outside, ground the inside smooth, then finished up by welding 1/4" plates on the inside. Looked good to me.

Quote:[It seems likely that this might a area of considerable stress (or at least enough stress to cause cracks in the same area on a few trucks).]

Well, that's interesting. I wasn't aware that this is a repeated occurance.Seems an odd place for that to occur.

Stop drilling cracks is common when repairing aircraft. It probably isn't necessary if you're going to weld the crack anyway. The one major problem I've seen from stop drilling by the novice is not making sure the hole is actually at the end of the crack. A liquid penetrant test as you suggested should tell you where the ends are.

This is true. Small cracks are often stop drilled and nothing else, other types of patching such as doublers and scab patches are added to reinforce the area. It' really isn't necessary if you're going to weld the crack because the weld does more than the stop drill to stop the crack from extending.

Another interesting thing to ponder... Rolled steel is very malleable and only cracks when work hardened. Work hardening changes the grain structure so I guess depending on how much of the surrounding area has been work hardened I could see how a crack could form next to weld.

Not sure what kind of heat treatment is needed to correct the grain structure in work hardened steel, but I'd be strongly tempted to preheat the surrounding area prior to welding.

I've been around alot of trucks in my life. There's alot of log trucks and dump trucks around here that have been stretched or had cracks repaired and were just arc welded and plated. I'm sure they've been worked harder than any pickup, alot more twisting and stress. The welds have held fine and haven't cracked around them. If you v the cracks before welding and then plate them they'll do fine. It's always a good idea to support the frame area while your working on it. Good luck!

Bob, other than the stop drilling, the factory manual tells you to do exactly what you first put down. Dress the crack, weld it, and weld a plate over it. There are specific recommendations for the shape and attachment of the backing plate depending on the area of the crack and how far it goes, but you're on the right track.

That makes perfect sense. Weld the crack to keep it from growing and bridge the potentially work hardened area with a reinforcement plate.

Just remember that not all frames are made from the same type of steel. See Czechman's posts.