Oh dear, I've broken my digger

[ProDave]

I've been finishing off the last bit of drainage, the rainwater drains. While digging the last trench something didn't "feel right"

But I carried on and finished that. I also flattened out a pile of soil while the digger  was around the back of the house ( dare I say the first bit of "landscaping").  It was then I realised what the problem was.

As I put weight on or take weight off the bucket, the king post is moving a bit.  Oh dear.

A look underneath reveals a chassis member supporting one side of the king post has cracked where it changes angle, I suspect a weld at that point has given up, so it's only being supported by the other side, which is flexing. Not good.

I think it's going to be a straightforward repair, just re weld the seam. But it will be awkward to do from below so I am hoping I will get better access from above if I take the floor plate out of the cab.

Watch this space, photo's to follow when I get around to lifting the floor plate.  No hurry, I have finished all the immediate digging jobs so it can wait if it has to.

This is the penalty for buying an old cheap digger.

Serious question. It will be welding about 12 inches from the diesel tank. I know diesel is a lot less volatile than petrol. Would you drain the tank? or just do it?

[Construction Channel]

Sad news  at least you caught it before the whole arm fell off.

 

how much diesel is in the tank and is the tank metal?

[ProDave]

Metal tank. I've only just poured another 20L jerry can full in there, so drainig it would be a problem finding something to drain it into.

Yes I don't want to carry on trying to use it, if the other part of the bracket breaks it would fall off and then be infinitely harder to fix then. As it is now, as long as I can get at it to weld it, it's fixable.

[Construction Channel]

I knew you had just filled it up  otherwise you wouldn't have asked.

im not going to be the guy to say its a good idea because thats a silly idea, probably best to wait for someone with some real knowledge on the situation,

have you got any thin sheet metal about you could hold between them to stop the actual sparks hitting the tank?

[SteamyTea]

36 minutes ago, ProDave said:

Serious question. It will be welding about 12 inches from the diesel tank. I know diesel is a lot less volatile than petrol. Would you drain the tank? or just do it?

Diesel just needs a temperature increase to ignite, gasoline needs a spark to the fumes.

 

Can you unbolt the tank?

[ProDave]

I haven't looked at removing the tank.

I know from experience, that petrol vapour will ignite very easily. Diesel you actually have to put a flame to it to ignite it, so i had thougt as long as I am not welding to the tank I should be okay?

[ToughButterCup]

7 hours ago, ProDave said:

A look underneath reveals a chassis member supporting one side of the king post has cracked where it changes angle, I suspect a weld at that point has given up, so it's only being supported by the other side, which is flexing. Not good.

Disaster, never mind NOT GOOD.

How about rigging a simple sheet of something to form a heat / spark shied between the welder and the tank? 

You've got me horridly hooked  Dave.....

Ian

[Declan52]

What about a wet beach  towel or 2 wrapped round the tank. 

And somebody on fire watch as you are welding. Start of with a few tacks just to see how easy it is to get in position before you start the proper weld. 

Can you not use a bit of hose and suck the diesel out back into the Gerry can.

[jack]

You're probably better filling it to the brim and covering the cap with a wet towel. More fuel = less temperature rise for a given amount of heat, plus no oxygen in the tank to allow combustion.

I'd do this in conjunction with the screen ideas above. 

[Temp]

Diesel just needs a temperature increase to ignite, gasoline needs a spark to the fumes.

Ah but Diesel goes whoosh, gasoline goes boom. Diesel is much safer for lighting bonfires. With Gasoline you can accidentally make a fuel air bomb. Don't ask. They grew back.

 

 

 

[ProDave]

One of the most nervous jobs I did once was replace the fuel sender in the tank of a petrol VW golf. I had dsconnected the battery so there could be nothing to make a spark but still had SWMBO watching over with a fire extinguisher and wet towel just in case.

[ProDave]

So here's the damage.

First the crack that I can see from underneath.

 

I think by removing the tank I will be able to get at that one from above. It's to far over to be accessed by removing the floor plate.

But I did remove the floor plate and here I found crack no 2

 

My guess is one of these has been cracked for some time and the other has only recently opened up.

I can close both gaps to where they should be by pushing down on the bucket.

The plan is to weld crack 2 from above with the tank still in place. This is much further from the tank but I will still dothe wet towel thing. I hope that will then be enough to hold both cracks closed while I drain and remove the tank to weld crack 1.

 

[PeterW]

That second one looks very clean ..???

are you planning on welding it up and plating over for additional strength ..??

[Nickfromwales]

51 minutes ago, PeterW said:

That second one looks very clean ..???

are you planning on welding it up and plating over for additional strength ..??

It doesn't look like you'll get much filler material into the crack tbh, so I'd say plate as well. Looks like a major stress point too. 

[Jeremy Harris]

2 hours ago, ProDave said:

So here's the damage.

First the crack that I can see from underneath.

 

I think by removing the tank I will be able to get at that one from above. It's to far over to be accessed by removing the floor plate.

But I did remove the floor plate and here I found crack no 2

 

My guess is one of these has been cracked for some time and the other has only recently opened up.

I can close both gaps to where they should be by pushing down on the bucket.

The plan is to weld crack 2 from above with the tank still in place. This is much further from the tank but I will still dothe wet towel thing. I hope that will then be enough to hold both cracks closed while I drain and remove the tank to weld crack 1.

 

Definitely looks like a very old crack.

 

When welding, don't empty the fuel tank, fill it right to the brim.  Diesel liquid doesn't burn, only diesel vapour is flammable, and then only when there is lots of oxygen around, so if the tank id full of diesel it's effectively inert and safe; any fire can only start outside the tank if the vapour concentration is high enough (which needs the diesel to be hot) and if there is enough air around..

I've welded near petrol tanks on old cars (Mini van and traveller rear subframe repairs!) many times, and the key was to fill the tank up to the brim, poke the TIG nozzle down the filler and just squirt in argon (with the power off, it displaces any air left in there) put a cold, wet towel over the filler cap (to cool any vapour that may escape down below flash point) and then weld in short sections, with wet rags to cool off hot bits and stop the heat spreading.

In your case I'd just fill the tank with diesel, put the cap on, put a wet towel over it and have a hose nearby so to can cool things down after a few minutes welding.  As above, it would be best plated on the top and bottom if you can (not the sides, there's very little stress in the web - the main loads are taken top and bottom).  It'll need a lot of grinding out, and I'd make a nice big vee down the break with the grinder and run several beads in there to fill it, concentrating on getting the best weld top and bottom, where the stress is, so probably best to start in the centre and work towards the top and bottom, so any inclusions are more likely to be in the near-zero stress region in the middle.