2022 - Yokomo GT-4W

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It's been a long time since I've done anything RC-related. I actually finished rebuilding this car last autumn, but I dragged my feet on painting a body for it for the next 9 months. Well, it's done now, so now I can show it off.

On its face, this is a pretty-much bone-stock Yokomo GT-4W -- and that in itself is an accomplishment, because these things are unobtainium in 2022. There's always someone selling their old nitro RC on eBay, of course, but old nitro RCs on eBay are a total crapshoot.

This one was assembled from two donor cars (which were absolutely filthy, as is traditional), some spare parts (including a lucky purchase of a brand-new Novarossi C12 engine), and some custom-made parts. The shocks and ball-end links are Tamiya, and the wheels, tires, and body are HPI, but the really interesting stuff is what I had to do to work around the parts I didn't have and couldn't get.

You see, neither of the cars I bought were the "RTR" model, and that meant they had a different arrangement for the central part of the drivetrain. The layshafts that the middle belt rides on are shorter in the non-RTR version, moving the belt and pulleys closer to the center of the chassis and leaving no room for an engine with a pullstart. This was going to be a problem for me, because I like pullstarts and I dislike starter boxes -- they work fine, but they're big and bulky and I don't want to carry one around. I managed to get my hands on the layshafts for the RTR version of the car, but I couldn't get the spacers needed to properly position the pulleys on the longer layshafts, so I made some out of aluminum tubing.

Also, while Yokomo made an adjustable tensioner for the middle belt, it only fits the non-RTR version -- if you try to rearrange the parts of the tensioner to line up with the middle belt on the RTR version, it interferes with the upper chassis plate and the exhaust pipe. So I took a spare set of belt-tensioner bearings and their accompanying mounting screw from a Tamiya XV-01, and I screwed them right into the side of the left chassis support. It's not adjustable, but it doesn't need to be, because I put it in the right spot to begin with.

I also couldn't get my hands on the RTR engine mounts which position the engine a little further to the right on the chassis, helping to make room for the pullstart on the back of the engine, so I had to make those too. Or rather, I used a technique I learned from previous projects, wherein I cut, drilled, and tapped a piece of flat aluminum plate to make an engine mount adapter.

I couldn't find a Yokomo clutch-style 2-speed transmission either -- at least not for anything resembling a sane price (I'm not paying $300 for a 2-speed transmission!) -- and I didn't want to use the centrifugal-pawl style that the car came with because they always shift very harshly, so I used some spare OFNA transmission parts that I've used on my HPI Nitro RS4s many times in the past.

You can also see in the picture above that I'm running a Centax-style clutch; this is the same HPI Centerforce clutch that I installed on my most recent HPI Nitro RS4 3, and it has the same flyweight mod to enable shifting at lower RPMs, so the engine doesn't have to rev-up to a screaming pitch before it can shift. That's fine for racing on a track, but not fine for driving on neighborhood streets.

Why not just use a normal clutch, if I'm so concerned about the shift RPM? Because I didn't feel like it, that's why. 😋 I have a dozen nitro RCs with normal clutches, and only two with Centax-style clutches, so this makes the car a little more interesting.

The steel gears on the clutch bell are from RC-Monster, who makes these gears for nitro-to-electric conversions, but they work just fine on actual nitro clutch bells too. And unlike the stock aluminum clutch gears, I won't have to replace them -- ever.

One last note about gears: In order to get the final drive ratio I needed for this car, I had to run larger spur gears than I've used on my HPI Nitro RS4s in the past, and that caused problems for tuning the shift point of the transmission -- I couldn't get the transmission to shift reliably at all within the Novarossi C12's rev range. Fortunately I had some modified 2-speed clutch shoes from a HPI MT2 that I converted to 2-speed several years ago, with copper-tungsten weights inserted into the clutch shoes to make them engage at a lower RPM; I wasn't using them in that truck anymore, so I put them back into service here.

One more honorable mention: I got some CVDs for the front axle, though strangely Yokomo never made them for the rear axle.

That wraps up the work I had to do on the engine, transmission and drivetrain. There was one last modification required, to make the GT-4W compatible with HPI body shells. I needed to shorten the wheelbase by 3mm, from 258mm to 255mm. Fortunately, that was very easy to do -- I just shaved 3mm off the rear edges of the lower-front suspension arms and added spacers in front of them, then I adjusted the caster shims on the upper-front suspension arms to restore the original caster angle.

Other than that, it's a bone-stock GT-4W. 😋 The body I chose is a Lamborghini Murcielago, because this car has an Italian engine in it, and the preparation of the body is my normal approach -- single realistic color with a few masked-off accent areas, optional headlight inserts installed for a little extra realism, aluminum tape on spots that I know will get scuffed, and a strip of adhesive felt tape where the exhaust pipe touches the body to insulate the body from the hot metal.

Those headlight inserts were a piece of work, but they look good.

The rear wing is color-matched, as I've done on a few of my other touring cars. The wing mounts required a little shaving on the outside edges to fit onto the Murcielago body shell, due to the shoulders on either side of what would be the engine lid if this were a real Murcielago.

Needing to modify the wing mounts reflects the overall experience getting this body to work with this chassis. There were a lot of tight fits, between the wheelbase, the wing mounts, the wheelwells, and the engine.

I like the way it came out, though. And it's a good thing too, because I put-off finishing it for so long that I might've just given up if it had turned-out badly. Even as it stands, I have no idea when I'll build another RC, because my interests seem to be shifting towards other things after 9 years in the hobby. But if this does end up being the note I go out on, it's a good note.

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