TheSamba.com :: View topic

Thu Oct 03, 2019 2:40 pm

Am I crazy to consider welding my link pin beam to my chassis?
I searched through many different forum topics but didn't really find any discussion on this.
I have a Hi Jumper rear engine chassis and will be fabricating a chromoly linkpin beam, stock width.
The reasoning is that it could become an integral part of the chassis.
The only reason that I can think of not to do this is that it wouldn't be removable if it got damaged. But if it is tied in well what are the chances of that?
Am I missing something?

Thu Oct 03, 2019 7:02 pm

You answered your own question about why not. Many weld it into the frame, and in itself is not an issue or problem until it gets bent or damaged. So there are quite a few people that have had to cut them back out.

Fri Oct 04, 2019 9:13 am

Thanks oldschool5er,
This is a light car probably under 1000lbs.
I am using stock link pin arms and spindles.
If i use 4130 tube and triangulate it well I am thinking the arms will become the weak link and the beam will be pretty safe.
Does that sound reasonable?
I have built a few rails in the past but always used an aluminum beam so welding wasn't an option. They were pretty much sand only.
With this car I want to do a little more off road driving and it will be street legal.
At this point I am thinking I will go ahead and weld it in unless there is some other major disadvantage that some of the vast knowledge and experience here hasn't pointed out yet.

Fri Oct 04, 2019 11:00 am

bugspray wrote: Thanks oldschool5er,
This is a light car probably under 1000lbs.
I am using stock link pin arms and spindles.
If i use 4130 tube and triangulate it well I am thinking the arms will become the weak link and the beam will be pretty safe.
Does that sound reasonable?
I have built a few rails in the past but always used an aluminum beam so welding wasn't an option. They were pretty much sand only.
With this car I want to do a little more off road driving and it will be street legal.
At this point I am thinking I will go ahead and weld it in unless there is some other major disadvantage that some of the vast knowledge and experience here hasn't pointed out yet.

Yes it sounds reasonable, the arms will bend especially stock link pin. Keep the beam supports out as far toward the shock tower as you can get. You would have to crash pretty hard to bend the beam.

Fri Oct 04, 2019 12:38 pm

I assume you will mig the front beam to the frame?

If you do, how will you anneal the 4130? I have heard it gets brittle when you weld it and need to heat it up to 500 degrees, hold it there, and slowly cool back down to not lose strength.

I'm curious because I have a 4130 front beam and want to weld some gussets to the beam and shock towers.

Fri Oct 04, 2019 5:18 pm

Well, I am not an expert welder but I have done my fair share.
Here is my experience with it.
I have never had a problem MIG welding 4130 to mild steel or 4130 to 4130.
You have to use the correct wire and let the weld cool slowly (air cool). You also have to do all the things that make a good MIG weld, like making sure the metal is clean, the gas is flowing correctly, the gap fits correctly, heat and wire speed are correct. Standard stuff.
I have also TIG welded 4130 many times and if that method is available it is probably preferable for really critical joints because it is a slower process and is much more controllable. Errors are easy to spot and cracks are easy to spot. MIG welding on the other hand can cover up many mistakes.
In this case I will be welding large parts that have lots of weld length, thicker materials, and very solid joints (I will leave a portion of the clamp) so I am not too concerned about it.
But I am not to old to learn either.

Fri Oct 04, 2019 5:42 pm

Just stay away from big rocks and you should be good! :D

Sun Oct 06, 2019 8:50 am

Wow
That is impressive.
I cant image your head is still attached to your body after that impact.

Sun Oct 06, 2019 4:52 pm

If, as I think is so, that bent rock damaged beam is the original to that frame, then my son made it and welded it in place. and made and welded the rest of the frame too. He says there should be no need to cut off the whole front clip. Just the bent beam. And since it was built as a play car without request or extra cost for 4130, the whole frame should be made of DOM, not 4130. And it is MIG welded as you can see.

My own experience regarding welding a beam on or clamping it is that both are fine methods.

My Hi Jumper seen in my avatar has the beam clamped in place. The beam has been replaced after getting bent in a flat out in high gear quadruple endo with a double twist. Fixing it did not involve any cutting or welding. Just bolt it in, align the front wheels and go.

I built my own Baja Bug with the original 1958 beam clamped into the cage work. Still working fine at 914,000 miles. No need to weld it in.

I've also welded in quite a few beams in various cars, Baja Bugs, tube frame buggies and tube frame Baja Bugs. I've cut a few welded ones out and replaced them after damage or to go to a wider beam.

When going to a wider beam, I consider it important to widen the frame structure it's attached to at the same time so the outer ends of the beam don't get bent more easily than a stock beam in a stock bug. Just as recommended by oldschool5er.

How much of the clamps are remaining in the Hi Jumper (if it is even a real Hi Jumper, as the majority of the buggy frames I encounter on here called Hi Jumper really are NOT)? If the clamps are there, you can weld to the clamps. Is there something wrong with the clamps that you need to weld it?

Pictures answer or prevent LOTS of questions.

One last comment...
If you're welding on a beam anywhere NEAR the bushings or bearings for the trailing arms, make DAMN SURE that the bearings and/or bushings are out of the beam 1st.

And 4130 can be quite successfully MIG welded. In fact, for small aircraft, the FAA recommends gas welding 4130.

Mon Oct 07, 2019 6:15 am

Richard - You seem to have a lot of experience with this sort of thing. You say you can mig 4130 to mild steel. No you need to heat treat the joints afterwards? If so, can this be done with just a torch? I don't have a kiln. Thanks.

Tue Oct 08, 2019 6:54 pm

I am pretty sure it is a Hi Jumper frame since it looks just like one and the PO (original builder) said that he "imported" it from California in the 80's.

This is how it looked after we brought it home and pressure washed it.
The kids were excited.

This is how it looks now getting a lower transmission mount, new nose cone mount and rear bars under the motor.
The original aluminum motor plate hanging the engine from above is probably OK for a street or sand only car but this one will see some two tracks and jeep trails.
As you can see it has a stock beam in it now and the clamps are fine. The reason I asked about welding the beam is that it makes a difference as to where I weld in the front floor bracing. If I keep a bolt in beam I will weld 1in diagonals from the center floor tube out to the lower clamps.
If I weld in the beam I think I will go the opposite way and go from the center of the lower beam tube and then out to the floor corners. If that makes sense.

Tue Oct 08, 2019 7:28 pm

Looks like a Hi Jumper (San Fernando Buggys) Sandsprite II to me... Its the same chassis as the one in my Avatar. I built mine in 1990 :D

Fri Nov 01, 2019 4:43 pm

1fastbigguy is right. It IS a Hi Jumper Sand Sprite2. Built at the end of my street in San Fernando in the same shop and by the same fabricator who built my Hi Jumper Ascot you see in my avatar.

They came equipped with the formed steel clamps you have, although the flame cut steel back/cast aluminum HD clamps were an option that was far more common on frames intended to be raced offroad.

I suggest you just stick with the clamps you have. I see NO reason to replace them.

Hi Jumper HD and race frames got diagonal braces of 1" x .065 tube from the bottom front cross member at the front end of the bottom center frame bar out to the bottom side frame rails just behind the bottom beam clamp.

Regarding post weld heat treat of 4130, FAA also says that for relatively thin material such as we use for buggy frames, post weld heat treat is not needed. regardless of all the back and forth BS and hot air amongst welders regarding 4130.

Mon Nov 04, 2019 10:20 am

Thanks for the confirmation on the frame. I have always thought the Hi Jumpers were a really good looking chassis.
I will try and remember to post pics as we make progress, slowly.