Nitro uncontrollable revving woes

[juice555]

I have a new Team Associated mini MGT 3.0.
Just broken in with 5 tanks.

I'm having a problem that is baffling me - and probably doing much damage to the .18 engine. FIrst of all, and I'm not sure if this is connected: I've noticed a high speed bog, which I now know is due to most likely a lean condition for the HSN. I will fix this before next run.
The problem rarely is after a high speed run, usually after switching to high gear the truck starts revving uncontrollably, without moving. Almost like its in neutral and decided to go full throttle. I thought at first its the crappy AM radio, so i replaced it with a 2.4ghz model, which doesn't seem to glitch at all like the AM one. This had no effect. I had figured the glitching pulled transmission servo halfway, putting it out of any gear, and held the throttle open. HOwever after today's run with teh 2.4Ghz radio it still happened. I ran back to the truck to see the throttle in its off state.
It might be because of air leaks in the motor...but why is it the truck doesn't move?! its in gear, but the engine just revs like hell. Once I hastily shut it off, wait 10 seconds, restart, everything is good again (when its cooled down???).

Any idea what this could be, and how to remedy????


(I've been running it around 2-5C temperatures lately.)

Thanks in advance

 

[Ballen]

it sounds like the slipper clutch needs to be tightend a little

 

[Metalhead Matt]

Sounds like the engine is tuned lean and the 2nd gear one way bearing is slipping. It probably got some fuel in it. A good cleaning with nitro cleaner should fix ya right up. I'd seal the engine before anymore running again to ensure there is no leaks.

 

[juice555]

thanks

Sounds like the engine is tuned lean and the 2nd gear one way bearing is slipping. It probably got some fuel in it. A good cleaning with nitro cleaner should fix ya right up. I'd seal the engine before anymore running again to ensure there is no leaks.

Thanks for the response all.
Do I need to remove the transmission from the center of the car to clean the bearing?

*I will seal the engine today before I run it again.

 

[Snook Man]

If slipping (high revs) in 2nd gear only the OWB would not be a factor, it only comes into play in 1st gear. A loose slipper clutch setting would be the 1st thing to check.

If slipping in 1st gear also then the OWB may be at fault, but a loose slipper would also cause the issue and is most common.

It would be easiet to remove the engine to get to and clean the OWB if needed.

 

[juice555]

If slipping (high revs) in 2nd gear only the OWB would not be a factor, it only comes into play in 1st gear. A loose slipper clutch setting would be the 1st thing to check.

If slipping in 1st gear also then the OWB may be at fault, but a loose slipper would also cause the issue and is most common.

It would be easiet to remove the engine to get to and clean the OWB if needed.

Ok, sealed the engine tonight. Also installed a rubber band on the throttle arm for a fail-safe.
I checked the slipper clutch and the nut was tight as possible. So, I guess it's not a slipper clutch issue.
i did notice some bad gear wear upon tear-down. i attached pictures of the worn gears. I guess this isnt normal.

well, hopefully next run with a richer high speed mixture and the sealed engine should fix the problem.

I still don't understand if the engine was revving that much why didnt the car move...

 

[tmaxxfreek]

nope that is not normal.... you need a new clutch bell as well

 

[hamz9561]

A rubberband is not a good failsafe. A good throttle return spring is necessary. A separate failsafe between the RX and the throttle servo is a really good idea to prevent a run away rig.

 

[juice555]

A rubberband is not a good failsafe. A good throttle return spring is necessary. A separate failsafe between the RX and the throttle servo is a really good idea to prevent a run away rig.

Point taken. I will find a suitable spring.
I was thinking a micro server on channel 4 with link to servo-operated fuel valve. The receiver fail-safe mode I would set all servos to neutral, except channel 4, which will activate the servo, and choke the fuel. [This could also be used manually as well if I can find a way to modify my radio to use a 4th channel.]
The only hitch I can see is the receiver battery dying that will foil my plans, however the plan is for telemetry, so I should have advance notice of this well into the future.
How does this sound?

---------- Post added at 1:20 PM ---------- Previous post was at 1:18 PM ----------

nope that is not normal.... you need a new clutch bell as well

Yea, didn't think so. I also don't think it's normal for this sort of wear to occur after 5 relatively easy tanks. At least I hope this isn't normal.

I'll replace the hub, and make certain to check the gear mesh properly and lube slightly. hopefully this won't happen again for a long time.

thanks

 

[juice555]

New developments

FYI,

I took it out last night and it never over revved.
Alos, I found the servo forward gear position not quite tightly pushing the lever into the gearbox. I think it was this issue that allowed the car to snap out of gear going forward. I did not previously reverse was absolutely fine and never went into 'neutral'. The reverse servo position happened to be perfect.
I believe the high speed acceleration, the transmission instantly going out of gear, and a leaking engine caused the uncontrolled revving.

Looks good so far.

 

[GypsieHunter]

Funny coincidence that this is exactly what is happening to me with my new MGT 3.0, right after break in and everything, however you managed to explain the symptoms much better than I could. I am very curious though what fixed the problem for you (slipper clutch, sealing the engine, transmission servo springs, etc) because I am still in the process of diagnosing mine.

 

[juice555]

Funny coincidence that this is exactly what is happening to me with my new MGT 3.0, right after break in and everything, however you managed to explain the symptoms much better than I could. I am very curious though what fixed the problem for you (slipper clutch, sealing the engine, transmission servo springs, etc) because I am still in the process of diagnosing mine.

Now, I've only run it for 1 tank since i 'fixed' it...so i can't tell you with 100% certainty that it's fixed.
But I attribute sealing the engine, and setting the little stop on the servo gear selector lever a little tighter so it pushes the gear selector lever in positively...there is a balance between too loose (problem occurs) and too tight (servo overworks contantly pushing the lever).
btw. my slipper is set as tight as possible (a la factory)

hope this helps.

I'll post again if my assumption proves untrue that the problem is fixed.