Art20c

Hi guys,
87 928 S4, Diamond blue metallic
Trying to repair small bent in area where bumper cover meets the driver side fender between headlight and side marker. Every time we touch it, it keeps on cracking. We weld it I believe 5 times, and it still brakes next to weld as soon as we put bumper back on, to see how it fits. Is there any secrets to deal with aluminum, or fender just has to be replaced?
Cracks are very small, about 2-3 mm in lengths, but my painter says that after a little while, it will be much bigger.

JHowell37

Hopefully you're using a Tig welder for this. You can technically Mig weld aluminum but I strongly urge against it as mig welding is much hotter and you're more likely to blow holes through the aluminum. I got fed up with chasing cracks in these ****ty fenders so on mine I just drilled a hole in the end of the weld and smeared a boat load of fiberglass reinforced filler into the back side to reinforce the whole area. I've already had one crack return but it's not really visible so I'm not going to lose sleep over it. Keep in mind that it's almost impossible to find a used fender without cracks. Even if you do, they're so ****ty and thin that you can crack them while transporting them. Some might disagree with my comments but I've walked through two Porsche junk yards this year and I make it a habit to run my hands along the fender lips of every 928 I encounter to check for cracks. I'm also one of the only ones here who has painted a 928, and replaced a quarter panel on one. Brand new fenders are outrageously expensive and unless they're secured in a crate, they can crack as easily as a used one.

My advice, try and solve your problems with modern plastics.

Lizard928

heat it with a torch first. then remove the dent.

Art20c

is there after market fenders made out of steel?
I found 2 fenders on internet fairly priced in decent condition, but now Im afraid of transportation

mark kibort

JB weld and sand. it will not crack

mk

JHowell37

I would not by fenders unless I could visually inspect them for cracks in person first. Unfortunately the Chinese are only shipping us their crappy windshields at this time. I doubt they'll ship crappy sheetmetal for this car as the demand isn't too large.

Podguy

Gas welding is the way to go on the alumimum fenders and doors. You have to have the surface very clean - use a stainless steel wire brush on the area to avoid contamination from aluminum oxide.

For cracks on the edges of the fenders I put a bit of a bead on the back. it is not noticable and will add strength to the welded area. You can use normal gas welding wire and flux - I got mine from the Tinman - Kent White. or you can use some 3 in 1 rod from Alladin.

JB weld and fiber glass is not going to do the trick. It will eventually separate. With the gas welding you can load on a lump of rod and then grind it to metal finish. One note of caution. Alumimun must be welded flat. Only a genius or very experienced gas welder can weld aluminum when it is vertical.

If you are having trouble with the crack following the new weld then you are not getting enough penetration on the weld and not preheating the area well enough. Cracking comes from the fender cooling too quickly. I use a bigger torch or even a heat gun to heat a wide weld area - maybe two to three inches around the target weld. I use a wet towel to bound the weld area so the fender does not absorb the heat and cool the weld area too fast. This also limits balloning and warping which the high heat promotes.

Often when I get done with the weld it looks pretty bad. But a little metal work and grinding and you can end up with a near perfect repair.

Once the weld is done I hammer it out a bit before grinding it down. The hammering actually adds strength to the aluminum by collapsing some of the metal. Heating expands the metal's thickness making it soft and weak. Hammering out the repair area thins the metal and makes it harder and stronger. I know this sounds weird, but this is how Aluminum works. The reason the fenders are as strong as they are and as difficult to get out dents is they are pressed thinning the metal and making it stronger and more brittle.

For dents I apply a little heat and work the metal. This will cause the aluminum to baloon out. Some times like on the hood you will end up with the tin can effect. To get the repair flat i use off dolly strikes. Just the opposite of steel. I also use a slap hammer with a towel wrapped around it to work a door to flat. When the metal is stretched too far then I use a heat gun to shrink it. Apply the heat gun to the area you want to shrink and then let it cool on its own. Again unlike steel where you would use a wet towel. oddly the wet towel will sometimes work too. Aluminum is weird.

I have been able to work doors, hoods and fenders to the point there very little filler is needed. But then again a little filler helps add some strength to worked aluminum. it is rare to find any used panels that do not need at least a little tweaking. If I had to rely on perfect sheet metal I would never get a 928 finished.

Good luck

Dan the Pod Guy

John Veninger

I'm a genius!!!!


A picture would help. Maybe welding on a back plate would help.