Below The Bondo

[rekievit]

So I have a dented tank, and a few questions on Bondo.
Its got a couple small ones, a big one on the side, and a bad one on top. By bad I mean severely creased, deep (~.75") but narrow and maybe 3" long. I think the PO must have dropped something with a hard corner on it.
I think I might be able to pop out the smaller dents and maybe the larger one enough to bondo it.
But the top one worries me. I read in previous posts that 1/8" inch is somewhat of a max depth for bondo applications like this.
My question(s): Who knows of something I can lay down before the bondo as a better filler for a large / deep application?
I read on previous posts something about a metal putty? Any one use it?
Does anyone know the extent of Bondo's power? Could I use it here, what are the consequences, ect?
As for the large dent (6" long), if I can't pull it out all the way is there something for a large patch like that?

Thanks in advance for all your help.

[Silent]

A friend once slammed his car door and had a footbal sized piece of bondo fall out. Best to move the metal to as close as possible to the desired shape before resorting to bondo.

[tarzan]

You can drill a couple holes and use a slide hammer then weld the holes.You can tackweld some pins to it to pull it out.You could also fill it with lead or liquid steel.

[Cobia]

re: Below The Bondo

I've had success in applying more than 1/2" of bondo and have it stick, of course you have to drill holes on the substrate surface on which it will anchor. You cannot/should not do that on a fuel tank unless you use a fuel-proof bondo. Does this exist? I don't know.
As an alternative I would suggest you grind or sand down the area to the metal and build it up with resin and fiberglass cloth to the desired level, then finish it off with bondo.
You would need to clean the surface with acetone after grinding it and use a resin which is compatible with the resin in the bondo you are using. Or buy a bondo which is compatible with the resin. After all bondo is nothing else but ground up material suspended in fiberglass resin.
Then you can feather it down to the desired contour, prime it and paint it.
Good luck.

[bikerphil]

bondo

IMHO, 1/2 inch would be the max depth with bondo. Could the dent be hammered out some by removing the fuel sending unit? JAT

[skids]

deep hole filler

If I recall correctly, I used epoxy and cut-up fiberglass to fill the side emblem cavities in the gas tank. Don't get too much catylist in it and make it too hot. Then you can use bondo to finish it. I have had it hot and very cold and nothing popped off. Denny Zander told me how to do it. You will find a post if you look for it.

[BEAR]

You can drill a couple holes and use a slide hammer then weld the holes.You can tackweld some pins to it to pull it out.You could also fill it with lead or liquid steel.

This would be my best advice actually but I would not weld anything on this tank until you take it to a radiator shop and have them boil it out for safety reasons many a mechanics who have welded empty gas tanks tell no tale...

[crazy steve]

On a dent that you have no rear access to, it's tough. Your best choice will be a slide hammer, but get one that will take a threaded screw in the end of it. Then get some sacrificial screws, tack-weld those to the dented area, then use the slider hammer to get as much out as you can. Carefully grind the screws off, then apply the plastic. No holes, so you're good to go.

There's a Pro setup that uses pins, but you need all the special gear.

As far as plastic thickness, you don't want it any thicker than you can help. On a car door or hood where you have a large, somewhat flexible panel and shock loads, yeah, the stuff can fall off, particularly with poor prep. But on a mounted piece like your tank I wouldn't worry too much. Rough the bare metal with a 36 grit disc before applying the filler; too fine a grit will reduce adhesion.

'78 E, original owner

[fredintoon]

Hi Rekievit,
first get the dents reduced as much as you can. The slide-hammer & brazed-on pins works as well as any.
And yeah, steam the tank out first. I know a guy who prepped gas tanks for welding by shoving the torch flame in the filler hole so the tank went whooof.
OK, he's a nut case even if he never came to harm doing that. Use steam, eh?
Then use the type of body filler that has long strand glass fibres mixed in it to mostly fill the deep dents. Finish off with normal or lightweight body filler.
Note that I don't say "Bondo". Bondo is a trade name and my stuff is Canadian Tire generic.

[thewiz]

There is a tool ...

called by a couple of different names ... one of 'em I remember is PopsaDent ... it uses a hot glue blob to bond a stylus to the panel your working on. Once this stylus is glued in place, the tool uses a screw 'bridge' to lever out the dent. I have used it successfully several times, requires no welding and is especialy good for small applications. I have seen them in Autozone and Kragan here in Cal ... but I bought mine off a TV ad.

[rekievit]

Response

To start, thanks for all the help so far

thewiz:
I actually have a pops a dent and gave it a whirl, problem being my paint was already cracking and so of course i ended up pulling paint off. It did work a little and I think I will give it another go after removing the existing paint.

fredintoon:
Definitely not going to stick a torch in it, good advice.

bikerphil:
I am not familiar with removing the fuel sending unit, easy to do? More importantly how hard is it to put back with no leaks? Seems like a good idea though and I think some of the dents are located in a good spot to be puched out from there.

Cobia:
I want to avoid drilling the holes of course, so the fiber glass is looking good. And thanks, I will make sure im mixing the right stuff.

Everyone:
So what I'm getting is pull out the dents by tacking a screw or pin and then using a slide. I am familiar with this but don't have easy access to a welder. If all else fails I will take do this though.
Question, what about an epoxy or jbweld to put a screw on there, do you think it will hold on? Then I can grind that off and bypass the whole tacking.
As far as filling, you guys mentioned liquid steel, fiberglass products and lead. Any specific product names of the first two you have used with success? And will they hold alright in a large flat application like the larger dent? Then I will cover with a lightweight.

[bikerphil]

I am not familiar with removing the fuel sending unit, easy to do? More importantly how hard is it to put back with no leaks?

It should come out fairly easily. Remove the bolts holding it in, then with a flat head screwdriver, carefully work your way around prying it up. The rubber gasket is pretty thick and should come out nicely in one piece if you pry it carefully. I've done it several times and never had a problem with the gasket. By chance the gasket breaks, they are still available.

[fredintoon]

Hi rekievit,
If you can't find oxy-acetylene gear I have used a propane torch to braze with low temperature brazing rod but that's at the extreme limit of what that gear can do. You could use a propane torch to soft-solder on a big head diameter bolt instead.
The filler I have used on deep dents is called "long strand fibreglass- reinforced filler" It looks like a mix of glass strands, polyester resin and body filler. Mix it with the red toothpaste and apply. I'd mail you my part-can but it's way past it's "best before" date and there's laws agin mailing the stuff anyway.
If you feel you must go with lead, use the proper 50/50 lead/tin filler that has the nice pasty stage between running and freezing and be prepared for it not to go right the first time. There's a reason that plumbers serve a 5-year apprenticeship. Don't breathe the fumes, neither. Even more so than when using resins.
And like bikerphil sez, the fuel gauge sender unbolts quite readily, just go easy on the gasket.

[crazy steve]

To start, thanks for all the help so far

As far as filling, you guys mentioned liquid steel, fiberglass products and lead. Any specific product names of the first two you have used with success? And will they hold alright in a large flat application like the larger dent? Then I will cover with a lightweight.

The 'liquid steel' (such as JB Weld) mentioned is really just a type of epoxy and will withstand heat, some chemicals better than bondo. Would work ok, but this stuff is expensive and hard to work; there's really no reason to use it here. Avoid fiberglass resin, as it's very hard to get a good bond to metal and the stuff can crack as it's more brittle than bondo. Also nasty to use. Lead has the many of the same issues as bondo when applied thickly and you need some skill to do it right. Also nasty to use and not cheap.

Plastic body filler got a bad rep because:

1. People didn't mix it right

2. Didn't let it cure right

3. Used it too thick in inappropiate places (anywhere that has part flex; not an issue on your tank)

4. Poor surface prep; THE MAIN REASON FOR PROBLEMS!

5. Won't fill large holes unsupported, but people try

I've seen this stuff work well in thicknesses up to 2". I did some bodywork on a car I bought and found it 1 1/2" thick in a door pillar that had been caved in. It had been there for years and hadn't moved a bit, even after untold cycles of slamming the mis-aligned door. If you have to go over a 1/2" thick, after doing the initial 'cheese-grate' let it cure overnight to let it shrink fully, then do your finish coats. Using the 'reinforced' bondo (containing fiberglass strands) for the thick areas won't hurt, then I'd recommend 'regular' for the finish coats. If you want to be POSITIVE it won't come out, then rather than sanding to bare metal, sandblast to bare metal the areas you put it on. Make sure the surface is clean/dry, and that stuff will STICK....

'78 E original owner

[crazy steve]

I should have also mentioned that bondo doesn't stick to lead very well; if a Pro has to fix a damaged leaded seam, they'll grind as much of the lead off as they can before putting on plastic...

'78 E original owner