Testarossa lower sill cancer and how to defeat it!

My 88.5 Testa was recently in for a clutch and during a cursory inspection underneath we found a little issue. There was some slight, but obvious separation of the lower sill area where it joins the main floor of the car on the UK drivers side.

This car gets driven two or three times a week, so there is a bit of dirt underneath, but all in all it's in pretty good shape. It's seen one wet road in my two years of ownership, and naturally Australia doesn't have the salt or sand issues found on USA / Euro / UK roads.

Here's a few pictures of what we found underneath:>


Once the car was home with the new clutch all was well until the fourth glass of Merlot after dinner one night. I had obviously been dwelling on it, so wandered down to the garage and low and behold, here's the Testarossa up on the hoist, right at eye level and ready for a check up probe!

Grabbing a small pry bar and a screw driver I began the cursory investigation! Poke, poke poke.....whoops, the screw driver disappeared!

Hmmm.....not good. Not much sleep that night and in the morning, I got into it.

Unfortunately I didn't get shots of what I found, so it's a before and after scenario, but this diagram of what a Testarossa sill construction looks like, will help in the explanation of proceedings.

I'll try and explain. Always hard because I'm working backwards to the way the car would have been assembled at the factory.

First I removed the 52mm x 1.2mm cover strip which as we can see in the pictures was the initial evidence of some cancerous growth. This buts up to the riveted floorpan sheeting and is tacked every 150mm or so with a small MIG tack.

It's held to the inner sill boxing section by a few small spot welds and is also bonded with an adhesive of some sort. Once this was removed it was apparent that the inner sill boxing wasn't in good shape, and that this cancer had started in the inner sill boxing and then spread to the cover strip as moisture in here has nowhere to go.

It wasn't long before it became apparent that I would need to remove the inner sill boxing to do this job properly. Not wanting to upset the spot welding, I ran the angle grinder along the top of the sill seam and then ran it along the base of the vertical section, basically cutting out a reverse L shape.

Here's the sill cut out:>

So the rusty part still left is the vertical section of the inner sill that is tack welded every 6 or so inches to the chassis rail. Next step was to cut that out which was pretty tricky as it's up about 45mm and you can't get an angle grinder in there.

I used a fine and very sharp cold chisel and then a die grinder with tungsten carbide cutter to remove the remainder of the welds. The damage does not appear to extend beyond the lifting or jacking saddles so I've cut out the material to that point.

At this stage I'd been at it most of the day and Suzie opened the garage door, arriving home from work, to be greeted by showers of sparks and the air full of rusty dust and grinding smell, and the visual image of me standing under the Ferrari with angle grinder in hand, getting stuck in!!

I think she nearly turned around and went back to work she got such a shock. Hey, it's not everyday that you take to your pride and joy with an angle grinder!

She settled down after a strong Scotch, and I got back to it after she left for the office the next morning.

Next I needed to remove the section of the inner sill that was spot welded to form the third skin of the main body seam. To do this, I used a centre punch and marked the centre of every existing spot weld, then using a nice new 6.5mm bit, drilled the spot welds through the first layer, but not going too far into the centre layer which is the strengthening gusset.

Once the holes were drilled I managed to use the same small, sharp cold chisel to remove the final strip of old metal.

Once the final section of the inner sill was removed it was time to clean everything up and treat the exposed metal with a rust converter / preventative solution. I use a product called FERTAN which is basically a Ferrite Tanate product which converts superficial rust and penetrates the sub strata of the metal forming a permanent barrier. You can prime and paint directly over it.

The tubular chassis rail isn't treated at all, and when the FERTAN hit the rail it really reacted causing the black that you see in these next pictures. Before applying the solution I used the angle grinder and a wire cup brush and really laid into the rail to get it as clean as possible. You can see some pitting in the surface of the tube, but I didn't want to grind this out, so have left it fully treated.


The car really has some quite interesting construction and design methodology, and here's something you probably haven't seen before.

Triangulating from the top of the sill and joining the main body seam there is a strengthening rib or gusset. When you step on the sill, the load is transferred through this gusset directly to the body seam where it is shared with the other sill and chassis members. To keep this gusset strong, it has holes pressed into it, just like the ribs on an aircraft wing.

The body seam is made up of three layers of metal, the outer sill, the middle gusset and the inner sill. In these images you can see that I have removed the inner sill, and you can now see the middle gusset and make out the round pressed holes in the gusset.


Here's what I took out of the old girl.

"Ode to England" I think I'll call this little lot!

Harsh but true, but not entirely what you think. More on this later!


Now that everything was cleaned, prepared, and preserved, it's time to put the new steel back in.

I used zinc coated steel sheet at 1.2mm thickness. This is the correct type of steel as used in modern cars, although some are only 0.55mm thick! None of that tissue paper for my car, so 1.2 it is.

The distance between the jacking saddles is exactly 1200mm so I made up two sections of steel. One to replace the inner sill which will be spot welded as per the original to create the third thickness of the originala body seam, and then be MIG tack welded to the chassis tube.

The other is 52mm x 1.2mm x 1200mm and is the extension of the floorpan that covers from the body seam to the bottom of the chassis rail, exactly as per original.

Here's the folded section in place ready for welding.


It's nice to have mates with good tools. Here's a 415v three phase spot welding machine sitting in the trailer and about to be unloaded. This will be used to do the spot welds, and hopefully once I have a bit of a practice on some scrap material, I will be able to place the new spot welds right on the originals to keep everything looking perfect.

The new inner sill will be welded in place, then primed and painted and then the final cover strip section will be welded and bonded into place. Then the final part of this saga will be to apply the Wurth under body deadener to recreate the original finish.

It's not an easy job, and not one to be taken lightly, but I'm pleased that I found the problem and have been able to rectify it 100% and keep the car as per original.


Well tomorrow is another day, but before I go, we must all ask ourselves how and / or why did this happen to my lovely car?

And here's the culprit:

You can see in this horrible picture, where the outer box section wraps around the front wheel arch and is welded under all of that body goo. See the little hole above? Well there is the reason for the water ingress.

We all have a rubber bung in our lower sills which allows access into the section of the sill UNDER the triangular gusset! But that hole is above the gusset and water getting in there has nowhere to go, so it sits in the inner sill, carrying dirt and mud along with it that deposits on the inner sill steel and rusts it away.

There are four drainage points along the sill, designed to let air in, and water out, but on the drivers side of my car, these were all gummed up, with a combination of body deadener, and road grime. The moisture couldn't get out!

I have a mate who's an IT guru, although I think he's a spy as he has some cool gadgets like optical fibre cameras! We removed the bung on the other side of my car and stuck his camera into the sill for a look. No sign of any corrosion, just an olive drab green patina on the steel which I think comes from the factory rust inhibitor.

Also, there are no holes in the inner guard to let the water in, and all of the drain plugs were clear.

So lads, get out there and have a look. Check your drain points and also have a look around your front wheel arch and look for holes where water could get into your sills.

I only have a four post hoist so I wandered down to a mate's place who has my two post (on loan) and we lifted the car that way to have better access to the sill. Suzie ("the Wife") followed me down with the spot welder and assorted tools in the trailer.

Here's the car on the hoist ready to make a start on the spot welding repairs.

The Snap On spot welder was fantastic. I changed the tips to allow a closer angle and we were able to place each spot weld directly over the original factory spot welds by first placing and holding one arm of the welder on the factory spot from the outside and then as the jaws closed, crimped and welded, the welds were perfectly placed.

Vise Grip clamps were required along the entire length to ensure that everything stayed in place but it really went well.


Once the spot welding was done it was time then to MIG the inner section of the sill to the tubular chassis rail. I used a formed block of timber here on a screw jack to apply just the right pressure for the new inner sill to meet the chassis rail perfectly and then MIG welded it in place.

When I had cleaned everything up, it was then ready for a good coating of metal primer with a good anti rust additive. In the first picture you can see a 10mm strip that has no paint. This is where the new sill cover plate will be bonded and the panel bon adhesive requires a metal to metal contact so I had to tape up this strip when I primed everything.


This is a drawing of my revised sill.

When compared to the earlier drawing you can see where I had to modify the original design so that I could actually get the MIG gun in there to do the welding to the chassis tube. Given that my steel is slightly thicker, still meets the chassis tube, and also triangulates to be stronger, I'm confident that this is a great repair.

Now it's time to do the last stage prior to the under body treatment, and that is to fit the new lower sill cover plate. This was a new strip of coated 1.2mm steel as per the previous drawings. This section is bonded in place and required 24 hours to set. I'll do it in the morning when I can set up a decent clamping process and show you the pictures tomorrow night.

This last component is non structural and is primarily used to extend the floor pan cover sheets from the tubular chassis rail to the triple thickness sill seam. Originally it is spot welded with only four or five small spots and then held in place by a bonding agent and the thick underbody deadener/sealer used at the time.

After consulting a couple of specialised local panel shops I opted for fixing this part by more modern methods and used 3M Panel Bond 8115, which is a two part epoxy adhesive designed specifically for bonding steel, alloy and fibreglass panels. It's dispensed from a two part cartridge with a special gun and is pretty nasty, sticky black crap to use, but amazingly strong and hard once it sets and cures.

After liberally coating the cover strip it was fitted into place and then supported with a long length of 4x2 to ensure even pressure during the bonding phase. A number of screw jacks allowed my to control the pressure and I walked away for the 24 hours required to cure properly.

I've picked up some Wurth under body spray and will be practicing on some cardboard sheet to get the spray pattern right so as to match the rest of the car.



After a couple of days I removed the timber and here is the result.

Tip for others: If any bulk adhesive forms when bonding, make sure you wipe it away when wet. There was a little left that squeezed out and I figured I would remove this later. Hahaha.........that stuff sets like steel. I had to use a die grinder and carbide bit to remove the little bit of excess that there was. Amazing.

From this point, any new steel received a coating of a rust preventative metal primer and then the car was prepared for the re-application of the underbody coating.

For this I used a Wurth product. Wurth Underbody Seal protects vehicle underbody, wheel housings and sills permanently from corrosion through stone chipping, road salts, etc. This permanently flexible rubber-plastic coating is impervious to temperature changes and can be easily cleaned.

You need to use a special gun to apply the product properly and I was fortunate enough to be able to borrow FerrariFixer's brand new Wurth 'schutz' gun which is specially designed for this application.

This is a messy damn job and you need to make sure that both the car and the garage are well protected or you will end up with black splatters everywhere. First thing was to mask up the car. I planned to redo all of my inner wheel arches and recoat the entire central underbody pan right out to the edges of the outer sills so there was a lot of masking up involved.

Once the car was all taped up, then I had to wrap the hoist and cover the carpeted floor, creating a nice little spraying booth to apply the underbody covering.

And here is the finished product.


As a final treatment, all cavities, channels, inner rails and doors have been sprayed with Wurth spray wax, which comes with a long tube that sprays a vortex swirl pattern to ensure total coverage inside those 'hard to reach' places.

It's been a tedious and somewhat difficult job, but I'm pleased that I went the extra mile to ensure that everything was cut out, treated, and then properly repaired. I'm quite confident that we won't see a recurrence of this problem again on this vehicle.

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