Haven't done much to do with aviation lately. Spring in mid TN is just not very good weather for flying underpowered foamboard aircraft, yanno? Nothin's wrong with the nitro Spear or nitro Mini Sportster, though, they're all good to go.
In the mean time, I got my hands on a Traxxas Slayer Pro with a blown engine!
Engine was pretty sorry. The piston/sleeve fit was completely ruined, zero compression whatsoever, which is why it wouldn't start when I received it. This was known before I bought it, only paid $200 or so for the truck and that was primarily because of the engine. I knew I'd be able to fix it, but that it wasn't operable as-is, so seller and I came to a pretty fair agreement considering the rest of the truck was pretty much mint and that a brand new one is nearly $500.
Quick way to tell if one of these engines will run at all is to try to do this. In an engine that will run, the piston will not come up to the top of the sleeve, and if it comes out this far it's totally hooped. This is why it failed to start.
If it had started, it would have thrown a rod pretty quickly. Big-end bearing is walking out of the rod
and has spun far enough off target that the oil hole in it isn't aligning with anything. I couldn't get my phone to snap a photo of something that small, but the wrist pin bore in the piston was also egg shaped significantly enough that the piston wasn't moving like it should have done,
further reducing compression, screwing with port timing, and all but guaranteeing that this thing would have never run right if it even started at all.
Since Traxxas 2.5/3.3 conrods are notoriously weak links that like to spontaneously fail...and because this engine was already undergoing rod failure when I got it...I decided to upgrade when I rebuilt the 3.3. Gave it a Davis Diesel conrod, far more stout and far better engineered than what was already there. Shoutout to Family Hobbies in Smyrna, TN for stocking these rods and for popping one up onto the counter when I mentioned I needed a new rod for it!
While I rebuilt the engine, I also rigged it for from-the-transmitter engine starting. Traxxas has an on-board electric starting system already, but they want you to use a wand containing a 7.2v nickel battery that you plug into a port near the back of the vehicle somewhere(You can see me using this in the first clip of it, where it failed to start). These wands work okay for cranking it over, but they're horrible about lighting the glow plug properly, and I wanted to be able to start the truck from the radio.
First thing I had to do was rig it to crank over from the transmitter. Since I use the same Futaba 6J to drive my cars as I do my aircraft, I had plenty of spare channels kicking around, and so I decided full right aileron would crank the engine over. A 10 amp relay controllable from an RC system handles the electrical side of things, and the receiver battery I use is perfect for this because it's high capacity and it has both servo-style and EC-3 high current discharge leads. The former I power the receiver off of, he latter I crank the engine from. Lithium-Iron-Phosphate chemistry, 2 cell, 2300mAh. Standard Rx pack in my surface and air fleet, and it really doesn't even feel the engine here.
With the engine turning, I then had to get the glow plug lit remotely. Parts wise it was easy, an off-the-shelf SwitchGlo system for RC helicopters and aircraft with a twist-lock plug connector did the trick. Now I could have mixed it into the cranking system and basically had it function exactly like the Wand, but there's situations where I might want to use one but not the other. Priming the truck, for example, I plug the exhaust and crank it over to force fuel up into the carb. This is done
without glow heat. And on a cold start I want to leave glow heat on for a few seconds after I've stopped turning the engine over, as well as if I need to leave it idling for an extended period as this is when these engines are most prone to randomly shutting off. So glow heat I put on the Ch5 toggle switch instead. And hey presto it's running again!
Following that I had to get it broken in properly...
and then got some good wheels and tires on it.
It's lookin' boss and running sweet!
If any of ya'll are at FPVFest 2019, be on the lookout. I'll be there, and this truck will come with me alongside my other two nitro surface rigs and all of my aircraft. And it
will go screaming across the grounds at some point, full throttle, second gear, flat out hard as she'll run! Hopefully by that point itt'l have FPV, reverse, and some additional tuning to make it drive even better. Needs thicker diff oil, sway bars wouldn't hurt, adjustments to spring rates, toe settings...mm.