Over the years I have done some rather difficult builds with lots of custom made parts, like the replicas of Atsuhiro Ohno’s Torpedo Optima from the 1987 Worlds and the Dyna Models Scorpion. But amongst the many cars that I would like to make replicas of, there is one that stands out, and that is Hiroshi Nakamuras Ultima based (loosely) 4WD “Nakamura Special” from the 1987 Worlds. This car I find particularly interesting, due to the high number of custom made and modified parts. Add that the car does not exist anymore and that there are very few good pictures of it, and you have what I feel is the “ultimate” challenge for a replica build. Thanks to Nakamura san himself, and to YF Lin who translated a Taiwanese article about the “SPL”, I do have a good idea which parts were used to put this together, but the challenge is taking it from the idea and actually build it.
Hiroshi Nakamura presents his “Nakamura Special” at the 1987 Worlds in Romsey, UK.
The Nakamura Special (just called the “SPL” from now on) was based on a Kyosho Ultima(ish) custom made carbon fiber tub chassis, a little bit wider than the original Ultima chassis, that was made using a hand crafted wooden mold. Of course the mold does not exist anymore either, so you probably already see what kind of challenges there will be with this build. It also has a custom made carbon top plate, and the whole assembly was very stiff and sturdy. I have talked about it with Mr. Carbon, my Finnish friend Jerry Hellström, and he has already made a carbon Ultima chassis, like the standard Ultima steel chassis. I will be working with him to make the chassis for the SPL, but that will have to wait until I get the gear boxes. The chassis being stiff and sturdy was a necessity as the 4WD was provided by a center shaft, much like on the Tamiyas and the Maruis of the time. That is not surprising, as Nakamura san was involved in the design of Marui’s shaft driven cars, like the Ninja and the Shogun, while working for the Proto design company. He was also the mechanical designer of Marui’s earlier chain driven Samurai, but had been working with shaft drive systems in the years leading up to the SPL. If I understood Nakamura san correctly (Japanese translations can often be a bit unclear in my experience) he had used this car to test shaft drive designs for Marui. The car used identical MIP gearboxes both front and rear, where the front gear box were modified and the top gear part removed. The MIP gearbox I have seen called different things, like SP-1 and SP-2, and I’m not really sure what the correct name is. But to be clear, it’s not MIP’s early gearboxes, but the later ones (see picture).
Unfortunately I don’t have any of those gear boxes at the moment, but my American friend Jeff Transou has drawn them in CAD, and will provide me with some 3D printed versions. I might have one original box coming from another American friend, Scoot Mike, but I will nevertheless use the 3D printed boxes first, and maybe change to original boxes when I have verified that everything works. It would be a shame to destroy an original box by cutting it wrongly. Like the first MIP gear boxes, these are also based on the Tamiya SRB gear boxes, and can use gears meant for the Tamiya. Since Tamiya have re-released the SRB’s, gears and other internals are relatively easy to find, and does not cost a fortune anymore. Luckily I did buy a few SRB ball differentials when they were re-released, and I believe I have just two left that I can use for this build. I have earlier mentioned that the front gear box was modified by removing the top portion. The boxes were also modified with attachments to mount the bevel gears used for the center driveshaft. On the original these gears were taken from a RC helicopter, and were the gears for the tail rotor. I have found some bevel gears that I believe will do the job, but have not figured out how I will make the mounting attachments, yet. One idea I have is to bend some steel plates, and then use 3D printed parts to hold the ball bearings, but I’ll figure that out when I get to that stage in the process. The suspension is from the Kyosho Ultima, with the front modified to take Kyosho Optima C-hubs and steering spindles.
The outdrive for the center drive shaft is taken from the top gear of the rear gear box and goes in to the center gear of the front gearbox (the top gear part is cut off, remember?). The top gear is, like on the Tamiya SRB, driven directly by the spur gear that is outside the box, on the right side. So what I had to do was to make a top gear asssembly with a longer shaft, so that in addition to mounting the spur on the right side, I could also mount the bevel gear for the center drive shaft on the left side. I did this by prying off the brass gears from two top gear assemblies (they’re just press fitted to the gear shafts) with a gear puller. At least I believe it’s called a “gear puller”, as I couldn’t find any other English names for it. In Norway we call it a “ters”.
I then used a dremel cutting tool and cut both of the axles where would be the middle of the brass gear, and the used the “ters” again to push them back into the brass gear.
As a bonus, I now have a spare brass gear that could be used instead of the plastic middle gear in the rear gear box.
I will cut the left side of the rear top gear axle and the front middle gear axle (now top gear actually) when I have the gear boxes in hand, to make it the right length for the bevel gears.
Here is a “mock up” of the drive train. I will have to use a longer drive shaft, but this is just to show the concept.
Well, this is it for now. I don’t know when the next update will be, as I still need the gear boxes to move further with the build. I’ll have to be honest, though…. this is probably the first time I’m not sure if I will be able to finish a build I’ve started on, but at least I’ll give it a go!