It's common now - even with cars from "dry" climates to have perforated rear shelves. I have a blog addressing how to check for the worst deterioration. But even a car that passes the test can have hidden secrets you can only find under the interior panels. In working on these cars, I do not worry about surface rust as the new life these cars will have is very different from the previous 40 years of exposure to the elements.
But once rust goes past the surface, it needs to be addressed. POR-15 is excellent at permanently stopping rust - even when it has pocked the surface. Pinholes can be fixed with POR-15 filler. Any spot you can get a finger through should be repaired with a welded piece, as penetration in one place usually means weakening in many other places.
This car had good gaps from the get-go - no prior chassis damage. But the right fender was a challenge, having been creased and stretched in front of the door. It took so many hours to hammer weld and shrink the sheetmetal that it would have been cheaper to buy a replacement fender. But there is an advantage to leaving a factory-installed fender in place. So I made the investment. As a result, the reflection down both sides of this car turned out perfectly straight - rare in a car not restored by a top professional.
While the chassis and body were remarkably rust-free, the rear shelf had been cut out completely. That was likely because of perforating rust, but at this point, it was just a guess. I had identified an excellent body and paint resource in Costa Mesa, near where I bought the car. I ordered a rear shelf stamping from Restoration Design and started on the transformation. As the picture shows, some holes had been cut behind the rear seat buckets, Really made no sense to patch them as the seat bucket bottoms were thin from corrosion. Back to Restoration Design for a rear seat stamping - and got that installed.
TRE got the engine running perfectly and as a double check, I put the car on a dyno. I was very pleased that the car put 193 HP to the rear wheels. A quite respectable <12 lbs per HP.
Depending on driving style, some people doing this installation would choose the transmission ring and pinion ratio that was original to the chassis. The 72 915 gearbox is magnesium-case, mechanical speedometer and 7:31 ring and pinion. The 72 (through mid 73 model year) 915 has an internal mainshaft seal, which can need changing out in as little as 30,000 miles. The mid-73 through 74 915 (and later) has an external mainshaft seal, which can be replaced without complete disassembly of the transmission.
This car got the later Carrera transmission, which has a stronger aluminum case, electronic speedometer drive
I had been searching for a chassis to build a new car in the style of the black Sinister 72.
In September 2012, I found a sad Sepia Brown 72 non-sunroof coupe (originally Sportomatic) with functional 2.7/915 installed. As far as I'm concerned, Sepia is a "get out of jail, free" card. I do not feel any obligation to keep that color...
I chose to use a rare, but available-in-72 color: Beige Gray #622. It's a very understated color, non-metallic and best described as "putty." As an admirer of Rob Dickinson's Singer cars, I wanted to do a sleeper: understated color on the outside, but luxurious monochrome leather inside. I planned to recover every vinyl surface with leather. I bought 5 full hides in Redmond Mocha, which is best described as chestnut.
The chassis got Bilstein front struts and aluminum S calipers, front and rear sway bars and 27mm rear torsion bars with Neatrix bushings. Car was lowered/aligned and corner-balanced by Johnson's Alignment in Torrance.
My intent from day 1 with this car was to show a "Singer
I wanted a monochromatic interior in an unusual, complementary color to the Beige Gray exterior.
I chose a color variously described as chestnut or reddish-brown. I purchased 5 complete hides to assure a perfect match throughout. I was able to find a carpet color close to the leather color...
You may note that the left door handle/armrest is a mirror
image of the right. I fabricated it. AIR did a french stitch and the result was really excellent, IMO.
I tried covering the dash myself. It was a waste of energy. AIR did it right. Recovering these dashes cannot be done correctly without a seam along the 'step' between front & rear. In the real world, the heat from normal sunny days will begin to separate any covering from the dash where the cover is stretched. The seam allows the covering to lie on the dash without this stress.
Note that the leather color varies with the lighting - from incandescent to fluorescent to sunlight. In real life, the color is consistent to the eye.
To finish off the interior, I commissioned TRE to cover their standard RSR style seats with my leather and cover the center cushions with closely-matching corduroy for comfort.
Merging a 3.2 engine and preserving the excellent Motronic
engine management system with the 72 configuration is
non-trivial. I took the car to TRE Motorsports in Van Nuys for that work. The torque and horsepower of the stock 3.2 is entirely adequate to move a 2300 lb. car around smartly. If you are like me, you will adjust to more horsepower fairly quickly and the installation on this car left some 'headroom' for adding 5-8% more HP between a chip upgrade and an exhaust backdate. In the case of this car, I left the factory setup intact, including stock heat exchangers and catalytic converter.
Because the car was destined to have a 3.2 engine, I wanted more than 15 x 6" wheels on the car. However because I was seeking a stock/stealth look, I used the 72-optional 15 X 7" Fuchs. To differentiate the look, I kept low-polish outers and media-blasted the centers and sealed them with matte clear coat.
AIR in Van Nuys was given the armrest/door handles to cover in my leather. They did an excellent job.
TRE further contributed to the build's safety by relocating the seat belt latch mounts to the center console and the lower, outer end attachment was created with a reinforced "bung" on the longitudinals.
One of the things you always want to address with a 3.2 engine is the fuel lines on top of the engine. These deteriorate after 20+ years and as they are high pressure lines, a failure can be catastrophic. I had TRE install new lines while the engine was awaiting installation. TRE found inconsistencies in the fuel injector output, so the engine got 6 new injectors as well.
Because the 2.4 T engine isn't a big heat-producer, this car had no oil cooling provision besides the engine-mounted cooler. I had TRE install hard lines the way additional cooling was done on the 85 Carrera 3.2 - with a new Carrera style cooler in front of the right tire. I did not remove the battery box with this car, as there is adequate air circulation in that area for the cooling demands of a stock 3.2.
(In the case that you have an engine that runs hotter, There are two steps to take to upgrade cooling: One is to remove the battery box to gain more airflow over the cooler. The second is to add a thermo-switched fan to move air over the cooler when the car is stopped. This was the solution Porsche used in 1986.)
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and 8:31 ring and pinion. As a result, it feels less 'torquey' than the earlier transmission, but runs somewhat lower RPMs at higher speeds.
Completing the chassis build, this car got a plastic fuel tank
as delivered on the Carrera RS and optional on all 73s (though
rare in North America).