The Story of Boris
My 300SEL 6.3 (affectionately known as Boris) was bought from the now defunct Gosford Classic Car Museum on the 24th of October 2017. It was delivered from Gosford to Canberra by truck, where it was taken straight to notorious Mercedes enthusiast and restorer John Green. John recognised the car, and produced a history file going back to 2001. John comprehensively overhauled the air suspension, a process during which many components were replaced. John explained that the previous owner had several mercs, and attached badges to their c-pillars.
Then I drove it around and enjoyed the acceleration and handling in Canberra traffic. An old Merc that looked slow, but without any modifications could beat most cars when the lights went green was just my sort of fun, until I snapped the driveshaft coupling that connects the back of the transmission to the drive shaft. The driveshaft coupling is a rubber disc, which allows vibrations from either end of the car to dissipate. It’s a known weak point for which John Green had a solution – he adapted the coupling from a later Merc, with a much bigger diameter coupling.
John Green warned me that the next weak-point would be the very complex roller bearings in the differential housing. The diff in these cars has a component where a number of small roller bearings run around a circuit, and a failure of this part usually results in all the bearings firing throughout the diff housing and gears, ruining the whole assembly.
John pointed out that the rear main seal was leaking oil. To replace the seal the engine had to come out. Even though everything was working well, it seemed like a good excuse to rebuild the engine and see what we could do to get a little something more out of it.
Research revealed that someone in Britain had managed to replace the complex mechanical fuel injector with more modern fuel injection, but this resulted in a very non-original engine bay. I wanted to keep the car as original and reliable as possible, so I ruled this out.
With the engine out, and the block stripped down, I had an ultrasound done to check the thickness of the cylinder walls, to see if boring the engine was a viable option. The measurements that came back were not ideal. I guess Waxenberger didn't have reliability as his highest priority when he created the 6.8. Since boring the engine to gain displacement wasn't an option, I researched the possibility of increasing the stroke to gain displacement. Turns out this was a good option, and I could get plenty of stroke, with plenty of room for more without compromising the engine geometry.
I found that such a crank would have to be completely custom. Further research unearthed a business in Western Australia (Galloway Race Engineering) who could machine a custom crank from billet steel to more than fit my purposes. I could send them the original crank and explain what I wanted from the new crank, they would then create a CAD design based on the old crank that would fit my new requirements, and use a CNC machine to do the rest.
The result was magic. The new crankshaft was significantly stronger and lighter than the original, and when paired with new, also much lighter and stronger conrods and pistons makes the engine much more satisfying to put the boot in. I had Galloway Race Engineering build the whole motor including very slightly uprated cams, and then ship it back to John Green to install in the car, along with having many of the visible components of the engine nickel plated, as when new. The engine bay had undergone a full restoration, including new stickers, and a thorough deep clean.
After tuning the highly complex but very flexible original fuel injection, and a full rebuild of the original transmission, including additional clutch packs, my wallet felt a lot lighter, and the car drives like a dream. The engine bay went on to win best of show at the Mercedes-Benz Club of the ACT 2023 Concours D’ Elegance.
The car has also undergone a full interior restoration. The headrests which were not legally required in 1971, have been deleted. The Carpet has been replaced. The seatbelts, a local dealer fitted option, have been replaced with fantastic-looking blue ones that match the exterior and carpet. The wood has been replaced with real Zebrano wood veneer which has a beautiful depth and natural elegance.
