2020 - Associated Nitro TC3
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Wow, it's been almost a year and a half since I wrote a "build complete" thread. Having a baby isn't especially difficult (or at least my baby isn't especially difficult), but it sure is a continuous effort. Weekends don't exist anymore; nowadays I sleep better on weekday mornings after my girlfriend takes our kid to daycare than I do at night on the weekends when they're both home.
Anyway, at some point I found time to build a Nitro TC3.
Why did I build a Nitro TC3 18 years after it was released and about 10 years after it was discontinued? Don't I have enough crap to worry about in my life these days? Yes, I do, but I still get bored from time to time, and apparently Me + Boredom = Questionable Decisions. To be honest, I would've been willing to get a newer nitro touring car, but the bottom dropped out of that market a while ago. It looks like the only nitro touring cars still being produced are either super-fancy dedicated racing cars, with no provisions for casual use such as liftable suspension and room for pullstart engines, or else cheap clones of the HPI Nitro RS4. Well, I already have five Nitro RS4s of various ages, and I'm sure not going to buy a cheap clone of a car I already have just for the sake of something different. So the Nitro TC3 was pretty much the only choice. Fortunately I was able to find several complete rollers on eBay -- and unlike the Nitro RS4 rollers that I bought a few years ago, the Nitro TC3 rollers I bought didn't look like they'd gone through a garbage disposal! Almost all the parts were salvageable, so I was able to build a nice car for myself, scrounge-up a pile of spare parts, and still have a complete roller to resell to the next person who wants one. That's just about the best possible outcome for resto-modding a vintage RC car.
That's not to say I got out of this project without spending a ton of money, though. The Nitro TC3 is still considered a desirable platform, so used cars that aren't beat-to-hell cost a couple hundred bucks apiece; also, I like my RCs to be just-so, and since every little thing in this hobby costs $20 nowadays, the price tag climbed quickly. In the photo above you can see several shiny blue parts: TRF shocks which I use on all my touring cars, Factory Team blue CVD axles, the Hitec steering and throttle servos that I like to use on all my RCs (okay, I guess those aren't actually blue), and TRF titanium turnbuckles for the rear camber and front steering linkages.
The shocks are worth a closer look, because like pretty much all of my touring car shocks, they look like they're stock TRF but they're actually a complete bastardization. To get shocks that fit the Nitro TC3 just right, I used TRF endcaps, Yeah Racing shock bodies from their 60mm rally-car shocks, special 28.5mm TRF shafts (2.5mm longer than normal) intended for the front shocks on the Tamiya XV-01 TC, and lower eyelets, spring cups, and springs from the HPI Nitro RS4 3 Evo. You probably also noticed the HPI engine I'm running in this car, in pictures shown above; yeah, I have no respect for brand purity in my RC builds -- all I care about is whether the parts I'm using are made well, fit correctly, and look good. (in the case of the HPI engine, it's less a matter of good looks and more a matter of me already having several of the same engine in-service in my RC fleet, so I have tons of rebuild parts available for this engine.)
Going back to the steering linkages for a minute: I found the stock servo-saver to be totally exasperating and a strange weak-spot in the overall design of this car. All of the rollers I bought had scrape-marks on the front-center drive cup, where the servo-saver adjusting screw had dragged against the surface of the drive cup as a result of the previous owners tightening the adjusting screws more than there was room for, trying to get acceptable performance from the servo saver. After seeing this and experiencing the same problem myself, I decided to take a different approach: I removed the servo-saver spring, cut the adjusting screw shorter, roughed-up the V-shaped surfaces inside the servo-saver, glued-and-bolted the servo-saver into a solid assembly, and fitted a TRF servo-saver to the steering servo instead. I'm much happier with this setup, even though I had to grind away some plastic on one of the front bulkhead support posts to make room for the TRF servo-saver. (it wasn't enough to compromise the strength of the bulkhead support, but it was worth mentioning in case anyone else tries this mod.)
Another platform-specific oddity that I had to deal with included the brake linkage, shown above, which is a strange push-to-stop design rather than the pull-to-stop design I'm used to seeing. That prevented me from being able to use the 2-in-1 HPI throttle/brake servo horns that I have on most of my other nitro RCs; that's a nice part and it bugged me that I couldn't use it here. The brake linkage also had a strangely weak spring that collapsed almost immediately, leaving the brake linkage to depend on parts flex for brake modulation, instead of having a spring of the proper stiffness to provide consistent brake modulation over the servo's full range of motion. Fortunately I was able to find a pair of HPI differential-stiffening springs from my stash of small springs (yes, I really do have a stash of small springs) that fit the bill and improved the brake modulation significantly.
Another couple of strange design choices were the exhaust header, which stuck way out to the side and required me to literally hit it with a (plastic) hammer to bend it in enough to clear the OEM body shell; and the exhaust hanger wire, which was originally just a straight length of wire that would've tilted the resonator way up at the front end instead of being level with the rest of the chassis. As you can see in the picture above, I added a couple of bends to the exhaust hanger wire to position the loose end further down and further forward to meet the resonator at its own level. Then I secured the exhaust hanger wire with a Traxxas pan-head servo mounting screw, because the stock screw relied on a sheetmetal washer to hold the exhaust hanger wire in place, and all of the rollers I bought had those sheetmetal washers deformed from engine vibration. I've always thought Associated had a strange attitude about expecting the owner to spend a day getting the small parts on their new RC to fit correctly, and the Nitro TC3 is no exception in that respect. Oh, and then there's the freaking English screws, which drove me nuts during the whole build. Why? Just, why? Finding flanged-and-serrated wheel nuts that would fit this car was exasperating, and I ended up just jamming some Metric wheel nuts onto the stub-axles after discovering that 6-32 threading is juuust close enough to M4 threading that the Metric wheel nuts would fit tightly but still be removable. Every other country uses Metric, and half the industries in this country use Metric too. I ask again, why use English screws on this car? And English ball-bearings too! Those are like 5x as expensive as Metric bearings unless I buy super-cheap non-sealed bearings! Grrrr!
Okay, enough griping about Team Associated's brand idiosyncrasies. I managed to score a nearly-new 2-speed transmission for this car, and I was pleased to discover that the Nitro TC3 uses a clutch-type shifter in the 2-speed transmission by default, whereas getting clutch-type 2-speed transmissions into my Nitro RS4s required custom-fitting parts intended for the OFNA Z10. I also found an all-in-one aluminum transmission/brake support piece from a brand called K-Factory (whom I'd never heard of before), and a couple aluminum suspension pivot blocks from them as well. It took a little bit of work to get them to fit just-right (what else is new?), but they stiffen the chassis quite nicely -- as if the hard-anodized chassis needed stiffening with all the carbon-reinforced upper deck pieces bolted to it. But hey, it's better to err on the side of too much chassis stiffness because it can always be modded to flex more if needed, right?
So that's my "new" Associated Nitro TC3. I've only been able to drive it a little bit due to the cold weather where I live, but it seems like a nice car, and will add a welcome bit of variety to my nitro touring car collection.
I switched to a Picco P12 engine that I scored on eBay. This accomplished 2 things:
1) The P12 appears to have lower midrange torque (not surprising), which means the 2-speed transmission doesn't slip as much when shifting, and I can actually hear it shift now instead of it sounding like the engine is hesitating at full-throttle.
2) I finally once again have a running Picco engine in my RC fleet. My first nitro engine was a Picco P-Zero .85cc engine in a little 1/16-scale nitro buggy, and the rest of the buggy couldn't perform well enough to keep up with the engine; even that tiny engine kept destroying diff gears, so I stopped running it. I've missed the tiny-F1 sound that Picco engines make.
Despite having 50% less displacement than the HPI T3.0 engine I originally used, and even though the fuel mixture is still rich because I'm breaking-in the engine, it still revs stupid-fast. The piston and conrod in the Picco P12 feel weightless in my hand, which undoubtedly contributes to its fast-revving nature. Too bad it's nearly impossible to find parts for this engine anymore; it was already old when the Nitro TC3 was released, to say nothing of how old the engine is now. I guess I'll keep the HPI T3.0 engine on standby for the day the P12 wears-out.
Every nitro runner has their favorite engine-break-in rituals. One of mine is to run the engine so rich it can barely rev-up for the first tank, and then drain the oil out of the exhaust onto a paper towel afterwards, so I can see what kinds of gunk got scraped off the inside of the engine during its first break-in run.
The black stuff is normal, probably microscopic steel and aluminum dust wearing off the crankshaft and piston respectively, but the sparkly bits were a surprise. I de-burred the cylinder sleeve with a diamond file before running this engine, and then I washed the parts before reassembly, so I didn't expect to see any chrome flakes in the oil. This is why it's so important to run an engine really rich for the first tank, and clean the combustion chamber with a cotton swab after the first tank; those chrome flakes can cause quite a bit of damage to the much-softer aluminum piston if they don't get washed out of the engine as quickly as possible.
Since I switched to an engine that (hypothetically) can rev higher than the HPI T3.0 I originally installed, I decided to install the "RPM-tuned" exhaust pipe to help the engine reach those higher RPMs. While building this car I bought a couple different pipes, but I hadn't been able to find a "RPM-tuned" pipe in bare aluminum. The blue anodized aluminum header does not react well to being re-bent (the anodizing cracks in a most unattractive way), so I used Easy-Off oven cleaner to strip a blue-anodized "RPM-tuned" pipe to match the bare aluminum header I already have. Then I sanded it with a 3M 2000-grit paint detailing sponge, and finished it off with some MAAS metal polish:
I can't say I actually noticed any change in performance, but maybe it's a subtle change and I'll notice it eventually. I'm busy running a couple different cars right now so that could be making it harder to notice small changes in each car.
I also figured out how to add a better fuel-pressure fitting to the exhaust, which just has a hole drilled in the side for a piece of fuel tubing to fit into -- not to mention the hole is positioned so the fuel tank interferes with the fuel-pressure tube. Not sure what Team Associated was thinking when they did that.
That is a right-angle tubing adapter with a tiny bit of tubing pressed onto the end inserted into the exhaust pipe, so that tiny bit of tubing effectively functions as a gasket to keep air pressure and oil from leaking out around the right-angle adapter. In this case the fuel tank helps hold the right-angle adapter snugly in the exhaust pipe, but the tiny bit of tubing on the inserted end would do that job well enough on its own if necessary.
I got bored last night and decided to modify the engine a bit, to wake it up and get higher RPMs out of it. (what good is it to have an engine that runs well if you don't take advantage of the opportunity to take unnecessary risks to make it run even better?) In previous engine-modding experiments I learned that side-exhaust engines tend to be limited by their exhaust timing, so I raised the upper edge of the exhaust port, and added Awesome Flanges™ to the upper part of the exhaust port to help release combustion pressure as quickly as possible at high RPMs before the transfer ports open. I was rewarded with an engine that revs audibly higher, though my apartment complex installed extra speedbumps recently so I haven't been able to get a proper speed-run yet to figure out what the engine's max RPM is.
The gearbox bearings spin freely. This car rolls more easily than all of my Nitro RS4s, even the shaft-drive ones. This car does 4-wheel drifts on pavement with no trouble, so it's making plenty of power already. I had to turn-up the shift point on the transmission because it was blowing past first gear in less than a second from a complete stop.
I was having a problem with the carburetor, though. If the engine idled for more than about 30 seconds, the next time I tried to accelerate the engine would choke and die instantly, even though the engine was idling well, not bogging-down with excess fuel. Even if I tried to gradually open the throttle, it would rev...rev...rev...rev...choke and die without warning. Basically, the engine would be overwhelmed by the amount of fuel needed to run properly at full throttle if it had a chance to cool-down a bit. So I adjusted the mid-range fuel delivery in the only way possible on a two-needle carburetor -- by modifying the taper on the low-speed needle:
The original taper is above, and the modified taper is below. I suspected that the fuel feed was opening too suddenly, and when I examined the shape of the LSN the blunt shape seemed to support my hypothesis. I rounded it off a bit so the fuel feed would open more progressively as the throttle is opened. Obviously I had to re-tune the LSN after changing its shape, but once that re-tuning was done the engine started behaving better. It bogs down some when accelerating after idling for a minute or so, but it's no longer an instant and irrecoverable choke-and-die scenario that requires me to do the Walk Of Shame to restart the engine.
More fine-tuning of the low-speed needle's shape. Throttle response is further improved by having the fuel mixture enrich more progressively as the throttle opens. If you're wondering why it's necessary, you can see a light-colored ring around the needle in the leftmost picture, where the low-speed needle bottomed-out inside the fuel feed when I reassembled the carburetor after initial inspection. The LSN in this carburetor is a VERY tight fit, and when it pulls out of the fuel feed, it happens very abruptly.
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