Defective motor?or something else?

[Panther6834]

Consider this an 'inquiry', so as to get a "general consensus opinion".

First, the original configuration: Dynamite 120A ESC, Dynamite 1900kV motor, run ONLY on 4S.
Second, the upgraded configuration: Seaking 180A V3 ESC, Leopard 3674-1400kV motor, run only on 6S.
Props: stock - 43.7mm w/ 1.6 pitch, alternate (CNC 4514) - 45mm w/ 1.4 pitch

Boat is rated for 6S on 'stock' electronics. Based on fully-charged packs, the 1900kV motor should achieve max RPM of just under 32,000 on 4S, and just under 48,000 on 6S. the 1400kV motor, on 6S, should have a max of just over 35,000 RPM.

Now the facts: After switching ESC & motor to the 'upgraded' components, boat was first tested running the stock prop, and the boat was run for approximately four minutes. The first 2-3 minutes, the boat was run full-throttle ONLY in straight lines, with approximately half-throttle when turning the boat around. The boat was then run at full-throttle, in an oval, for the next 90 seconds, and then brought in to have temps taken on all electronics. Other than some "hopping" (indicating the trim tabs might need a slight downward adjustment), the boat runs fine. Temp checks showed everything running quite cool (I don't remember the exact temps, but ESC & motor were below 100, and the two 3S packs (run in-series) were just slightly over 100...in other words, "cool").

I made a slight adjustment (down approx 2mm) to the trim tabs, swapped the stock 4416 prop for the CNC 4514, and swapped the LiPos for a couple of fully-charged packs. I should also mention that another boat was running during this time, so I waited until the other boat was back to shore before putting my boat back in the water again, which was approx 10 minutes. Following the exact same testing procedure, the first 2-3 minutes were spent doing straight full-throttle sprints, with "cool down" periods of half-throttle at each end while turning the boat around. This was to be followed by the same 90 seconds of ovals at full-throttle. Unfortunately, after completing the second lap, and just past halfway through the first turn on the third lap, the boat 'stopped'...she was "dead in the water". It took about 15 minutes to recover, and, upon recovery, I noticed the distinct 'hum' of the servo, telling me that it wasn't the batteries (initially, I thought the LVC had failed, and the boat had no power), and, in all likelihood, the Rx & ESC were probably fine.

As soon as we were back to the workbench, I immediately removed the canopy, and a tiny 'whiff' of smoke exited. I took temp readings, and, while the batteries and ESC were slightly 'warm', it was the motor that worried me - after 15 minutes, the motor was hot...as in, 130 degrees. I quickly grabbed my Tx (I know what you're all thinking -- I should have immediately unplugged the batteries), and tested the steering, and the rudder turned both directions. So, I knew the servo & Rx were fine, and (once again), in all probability, the ESC was fine. Next, I tested the throttle...and nothing. Now, I disconnected the batteries, worried that this brand-new motor, which should have been running cooler than the stock electronics, was fried. It wasn't until a couple minutes later that I noticed one of the wires coming from the motor was no longer connected to the bullet connector, at which point I thought the motor might be ok.

Here's the thing about the bullets - the stock bullets that came on the motor were 6mm, and the stock bullets that came on the ESC were 5.5mm (I know they're listed as '6mm', but, in truth, they're closer to 5.5mm, as they just fell out of the motor's bullets)...so, I cut off the ESCcs bullets, and soldered on the bullets that came with the motor. As such, all three bullets on the ESC's side of the connection were soldered by me, and all three bullets on the motor's side were soldered by Leopard. This led me to believe that Leopard did a sub-par soldering job, and, in re-soldering the "detached" bullet, I had also planned on checking the other two.

However...and, it's a big HOWEVER...I am no longer going to be re-soldering the bullet. In further troubleshooting, I discovered that the insides of the motor are 'toast'. No, I didn't take it apart...I didn't need to. If you look at what I saw, looking into the end of the motor, you will see.
You could say that the motor attempted to pull more amperage than the ESC could supply...but, considering that the motor draws a maximum of 58A, and the ESC runs at a 'constant' of 180A, this wouldn't make any sense. Likewise, one could say that a load increase caused the motor to excessively heat, which would have fried the motor, and, in turn, could have caused the bullet to de-solder. Unfortunately, this also doesn't make any sense, as the 1mm larger diameter prop had a much lower pitch (1.4 vs the stock prop's 1.6), thus the load on the motor was lessened, thus the electronics would have been even cooler. For those thinking "something else", such as moss bound up in the prop, know that the prop, strut, and rudder were clean as a whistle. This was a brand-new motor, being powered by a brand-new ESC. I had previously assumed that the ESC, Rx, and servo were all still good...and, two days later (today), I confirmed this, by connecting a different motor to the ESC, and testing everything...and everything worked.

So, WHAT went wrong? This is the reason for this thread. Based on the facts, the only logical conclusion I can come up with is that the motor was defective. I might still be somewhat new to FE boats, as well as marine RC motors...but, I am more than familiar enough with RC motors, in general. I understand that 99.9% (probably higher) of RC motors have no problems...but, that doesn't remove the fact that, every so often, there will be a motor with a defect...and, unfortunately, I believe that I got that 0.1%. I'd like to hear other people's thoughts. Based on all the facts provided, what do you think? I would really like to know other people's opinions on this matter.