Mercedes Benz 190SL

Preparing the undercarriage to accept its first coats of paint was made easy with the body rolled to its side. The entire undercarriage was acid washed with POR15 Metal Ready in a plastic spray bottle after cleaning with panel wipe. The spray allowed the acid to be sprayed deep into the joints. Several coats were applied with a hard brush and 3m Scotch Brite pad until all signs of surface rust were removed. The acid was continually sprayed with water from a plastic spray bottle to keep the acid from drying and to reactivate it. After soaking in acid for 20 minutes the floor was thoroughly washed down with warm water and immediately dried before any rust formed.

The dry floor was then sanded with 3m Scotch brite pad and cleaned with panel wipe and degreaser. I used a Devilbiss GTI gravity feed gun with a 1.4mm tip to spray the floors with three coats of PPG DP40 epoxy primer. This should provide sufficient coats to seal the metal over which was sprayed 3M smooth anti chip coating, Grey part number: 08886. I like this product as it is smooth and overpaintable and sharing the same, robust anti-chip benefits of the textured product, 3M™ Smooth Coating dries rapidly to an excellent finish. Applied using the pressure adjustable air-fed 3M Pressure Pot Stonechip Applicator gun gives the best results.

The joints were seam sealed with Wurth Polyurethane adhesive and sealing compound. Product 0890 100 2 Grey using a hand application gun. A further coat of PPG DP40 epoxy primer will follow three coats of PPG's DAR 4065 "Sandalwood" Semi-Gloss tan/grey.

Ensure that before any original floor pans are removed that you mark the locations of the brake and fuel pipe clamps and ensure these are drilled before painting. If using original mounting clamps ensure that square holes are drilled and pre-fit the pipes, clamps, fuel tank and fuel filter to ensure location is correct. This was aided as the body was rolled onto its side. Additionally before painting ensure that the two holes for the rubber exhaust bumper are drilled in the right hand front floor pan. The fronts of the floor pan that meet the lower firewall panel were originally factory bent at a ninety degree angle and upwards. This will cause an obvious water trap. I decided to seam weld at this joint and cut of the lip by grinding back. Push plenty of seam sealer at this point, when I say push do not use a brush, instead use a putty knife to ensure it is as tight as can be.

Posted by webmaster at 06:29 PM | Permalink

The old pitted floor pans were stripped and new pans welded while the car was on jack stands on the floor to avoid distortion of the chassis. The chassis/frame was in superb condition except for on or two places, which required local repairs. The floor pans consist of four separate panels factory spot welded to the chassis 'n' shaped side and cross members from beneath the car. This forms a box section which was not sealed, primed or treated by the Mercedes-Benz amd results in rust from the inside out. The replacement floor pans are thickers than the original and are two sided zinc coated steel. The zinc coating creates a barrier against rust and can be painted over once prepared well. All chassis members should be checked carefully by tapping with a pick hammer to ensure that they are not weak, especially the trailing arm supports which could become critical if the trailing arms were to break loose at high speed.

The SIP 170 turbo Mig welder performed nicely but welding on you back with overhead plug welds took time mastering. Too low a speed and rating on hte Mig welder and the weld would not hold up. Too fast a wire speed and too high temparature the weld will fall out, hopefully missing your arm. Precautionary measures should include full body and head protection, safety first. I sort the advice from a Hot Rod forum, HotRodders, and this was the response by one of the members:
"Remember to work the pool. If the weld is falling out of the hole, two things to look for here.
1) You probably actually have too much heat or moving too slow and the weld is molten to the point that it is sagging under its own weight. Gravity is getting you there.
2) Also make sure that there are no gaps between the 2 pices of metal. If this happens, it not only is a bad seal, but it makes it a bear to weld vertical plug welds.
If the tacks are not holding, again it is a missed location of weld or lack of penetration. A lack of penetration may be from weld technique or heat. I really doubt that it is heat since we are talking relatively thin sheetmetal here. When doing that type of plug weld, I usually try to start in the middle of the hole and work the weld out to the edges while circling around the entire inside of the hole. If you see the molten pool starting to sag, stop for about 3 seconds and hold the torch in the same spot. When it is too dark to see the pool through your helmet, hit it again and finish the weld.
Overheald welding is probably the most difficult if that is what you are doing. If you take two pieces of sheetmetal about the same guage, set them together on the ground or bench, you can tune your welder comfortably before trying to overhead weld the floor pan. Look at the backside of the second piece of scrap. You should see where the heat has penetrated through it. Not fused material like a pimple, but just enough to discolor the metal outlining the weld from above."

Armed with this advice and with several practice runs I mastered the overhead plug welding.

While the car was on jack stands I built a trolley. This was rigged with two protrusions to one side clear of the body so as to provide a pivot point when rolling the body over its side. Next process is to complete the grinding, de-rusting and preparation for paint. Much easier than working under the car on your back.

Time now to attend to the right hand wheel well, which was previously badly repaired by plug welding rust holes. The lower portion was cut cut out. An new repair panel was fabricated complete with drain hole. This was butt welded an finished off by lead loading.

Posted by webmaster at 10:53 PM | Permalink