2025 - Kyosho FW-05RR 4-Stroke

I've had lots of RCs that took me a long time to finish. This one took me a long time to start.

Three years ago, I bought this car as a ready-to-build kit, including the 4-stroke engine and the conversion kit, on eBay from someone who I guess never got around to actually building it themself. I already had some experience with 4-stroke engine conversions from my HPI Bullet MT 4-Stroke, so this one looked like it would be fairly easy by comparison, having all the required parts in a nice little factory-sealed bag. I had other projects to finish up first, though, so I chipped away at those while this one sat on the floor of my office, though I did take apart the engine and send the crankshaft to a machinist to be turned-down to fit a standard 7mm flywheel collet. (I ended up using the factory-conversion clutch instead, but it's nice to have the option to put a brass BuKu clutch on there someday if I need to.)

Before I finished chipping away at my other projects, my home life exploded, and I had no energy for hobbies for a long time. The FW-05RR kit continued to sit on the floor of my office for another two years, until about this past June when I finally started taking it seriously again. It took me until December to actually finish it, but 6 months isn't a long time compared to 3 years. 😅

The star of this build is obviously the O.S. FS-26S-CX engine, so let's just get right to admiring it:

Isn't that pretty? 😍

Here's a closeup of the PCV system I installed, based on lessons learned from working on the FS-40S-CX engine in my HPI Bullet.

It doesn't look like much, and that's because I finally got the required modifications sorted-out well enough that it doesn't need complexity to work right. For the sake of brevity, I'll refer you to this post for details about the internal engine modifications. Thanks to those modifications, now the only external components are a pressure vent on the side of the rocker arm chamber, a vacuum hose, and a vacuum inlet carefully positioned at the carburetor's idle gap so there's always reliable suction to keep oil vapor moving through the engine. That's important because oil vapor is the only lubrication the engine actually has, and its extremely discontinued so it's not like I can just go buy another one if I trash it. The car version of this engine is exceptionally rare, so this one basically needs to last forever with nothing more than conrod and ring replacements from time to time. Here's hoping. 🤞

Aside from the modifications to the engine itself to make it lubricate itself better, the only other thing I had to do to make this conversion work -- no big deal or anything -- was...y'know...cut a hole in the chassis.

Admittedly that was my own fault, not the kit's fault. All of my nitro RCs have pullstarts and I fully intend to keep it that way, but the engine mounts in the 4-stroke conversion kit assumed I would be using the version of this engine that doesn't have a pullstart. O.S. pullstarts are big and bulky compared to most brands, so even with some extra shims to raise the engine mounts as much as practical, I still had to...*ahem*...clearance the chassis plate a bit. Now that I've done it once, if I ever have to replace the chassis plate again I will know exactly what I need to cut away, instead of needing to err on the side of removing more than absolutely necessary, but whatever. I'm not going to be landing triple backflips off skate park halfpipes with a touring car, it'll be fine.

This engine revs low compared to pretty much any 2-stroke engine, so the conversion kit came with larger pinion gears and an engine mount that positioned the engine further away from the centerline to make room for those gears. It also tilts the engine inward a bit to correct the weight imbalance somewhat. The gears, though, are anodized aluminum, and there are no more-durable alternatives I've been able to find. The anodizing looks to be fairly good quality Type 3 hard anodizing, but anodizing always wears off eventually (especially when scraping against glass-filled nylon spur gear teeth), so to give them a little better chance of surviving long-term, I lubricated them with some White Lightning ceramic/wax dry lube. Normally I wouldn't lubricate exposed gears at all, because there is no lubricant that dust won't stick to, but ceramic/wax dry lube is at least one of the better ones in that regard, and wax has a strong film strength.

Aside from the engine, this was a pretty box-standard build with pretty standard upgrades. As shown above, I determined the fiber brake pads from the newer FW-06 would fit the FW-05RR's brake system just fine and give more predictable braking. And as shown below, I hunted down CVD axles to replace the loose dogbones. Not shown at all are the hardened steel diff gears I got to replace the pot-metal gears the kit came with, but you know what diff gears look like, so it's all good. Oh, and I used a hex screw kit instead of the coarse-threaded JIS screws that came in the kit, because I appreciate being able to take things apart to service them without damaging them a little bit more each time.

Oh wait, I guess an honorable mention goes to the homemade gasket I had to make for the 90-degree carburetor adapter, because the stock gasket O.S. provided for use with this engine didn't seal the 90-degree adapter properly when it was mounted in its slightly-tilted position to compensate for the tilt of the engine.

Fixing that stabilized the air/fuel ratio, unsurprisingly, and also got rid of a nasty oily film that kept accumulating on the back of the engine from fuel spray sneaking past the OEM gasket.

- - -

Okay, that wraps up the mechanical stuff. Now...(sigh)...now I have to talk about the paint job.

It looks lovely, doesn't it? I certainly think so. But oh my god it was a nightmare...and it was almost a disaster.

It took me a while to decide what body to put on this chassis. I was kinda feeling a vintage turbodiesel vibe, thanks to the high-torque low-RPM 4-stroke engine, but the number of 200mm touring car bodies designed after cars that actually had a turbodiesel option are very limited. I ended up going with the BMW E30, which meant one of my other touring cars will need to be re-bodied now (but that's a different topic), but the bigger problem is that I haven't painted a BMW E30 body in 10 years and my skills have improved enough that I couldn't let myself get away with doing this again:

That was fine for my first-ever hand painted RC body back in 2015, but much to my own aggravation, I have standards, and one of those standards is to not halfass something I know how to do well. The problem is, painting a BMW E30 body well requires a lot of layers of paint, because it has details like chrome bumper trim and black lower valances that modern cars don't have. And the deep metallic brown color I wanted was going to require two layers of paint just by itself, gunmetal behind transparent brown. And the chrome was going to require several coats of sealant to protect it from the black backing coat. And all of this stuff was going to have to be masked. Oh god, the masking.

The masking around the bumpers, specifically, required multiple layers of masking staged in the correct order so I could peel them off one by one to expose each part that needed to be painted a different color, and the lines needed to be as close to perfect as I could get them, because if there's anything that looks worse than overspray on clear lexan, it's color bleed between two contrasting colors -- and you can't really get more contrast than black right next to chrome.

I know there are people who enjoy painting RC bodies, but I don't. I like when they're done and they look good. The actual painting process is an obstacle to be overcome. And that, dear reader, is where things went horribly wrong.

You see, after days of washing and scuffing and masking and trimming masks and planning the paint order and making sure I actually had enough of all the colors I needed, I was firmly in "Get This F***ing Thing Done" mode by the time painting day arrived. And with the weather getting chilly, I didn't have long stretches of good painting weather to work with anyway. So while I had everything planned out and staged and ready to go, my impatience found the one hole in my plan -- I hadn't factored in the amount of time necessary to let each layer of paint cure before applying the next one. And when I reached the point where it was time to paint the chrome bumper trim, the chrome did something I failed to anticipate -- the tiny overlapping flakes of aluminum (unlike normal metallic paint, which has gaps between the aluminum flakes) sealed the paint surface and trapped the chrome paint's extremely aggressive solvent underneath it. The other colors I'd already applied, the transparent brown and the gunmetal, started to reliquefy, bubble, and detach from the lexan.

It took 3 days before the paint re-rubberized enough that it stopped conforming to my fingerprints with the lightest touch, and then I had to cut around the edges of the damaged paint and remove it and try again. Even 3 days later, the damaged paint was still soft enough I was able to scrape it loose with my fingernail, and the transparent brown paint was so thoroughly destroyed I was able to clean off the residue with 70% rubbing alcohol. Given how easy it was to clean off, I'm pretty sure the transparent brown paint wouldn't have been set properly ever again, even if I'd given it a year to cure. Not that there was any point, since it was damaged and needed to be removed anyway, but that's just an indication of how far gone it was.

But, despite my newly rekindled hatred for trimming and painting Lexan, ultimately the spirit of "I didn't come this far to give up now" eventually won out, and I repainted the damaged area and matched the original color as best I could -- slowly, this time.

After that it was pretty straightforward; I peeled off the final layer of masking to expose the parts that needed to look like black trim and painted the rubberized black backing coat (did you know Duratrax paints are out of production now? I didn't. 😡) And then I sprayed the fuel-resistant clear acrylic sealant. And then I trimmed the overspray film on the outside and sprayed the matte outer coat to make the black trim look textured instead of glossy. Aaand then I cut holes in the front and rear windshields to cool the engine. AAAaaand then I stuck foil tape and adhesive felt on various places inside the body to protect it from exhaust heat and tire scuffs. AAAAAAaaand then, lastly, I trimmed the foam bumper to fit the body correctly.

Oh yeah, I also got the crazy idea to buy some yellow headlight vinyl and give my "vintage turbodiesel E30" some equally vintage French headlights. Because I hadn't done enough work already, I guess.