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So my son got a b4.2 for his birthday and today we took it out for the first maiden run. After maybe, I don't know, 10 minutes of rooster tailing around in the dirt, I noticed something wrong sounding with the gears, so I told him to turn it off and bring it inside.

When I pulled off the gear cover, the result was not pretty. It's almost as if the pinion had eaten into the spur gear!

(Click for higher res)

I admit that I did not check/adjust the pinion/spur mesh before we took the car out, because I assumed that "ready to run" meant, well, "ready to run."

So, it goes without saying that we're gonna need to get a new spur gear now (the boy is less than happy about this). What I'm more concerned about is why this happened. Would a pinion that was meshed too tightly do this, or is there something else that I need to investigate?

Did he take it off any gnarly jumps? Rough landings? The motor could've simply moved. Or, some debris got in there and wiped it out.

scr8p wrote:Did he take it off any gnarly jumps? Rough landings? The motor could've simply moved. Or, some debris got in there and wiped it out.

No gnarly jumps to take, as it was just relatively flat terrain with a few tree roots here and there.

There were some clumps of grass that he got hung up in, and there were a few times that the car was stuck, but the wheels were spinning as he was mashing the accelerator trying to get it free. I didn't see any foreign material on the gears when we took it inside and pulled off the cover.

Yeah, RTR isn't really 'RTR'. It just means that its been assembled but in reality you still need to check a few things and gear mesh is one of those things.

Another thing is the slipper clutch settings - it may have been too tight and so when your son was mashing the gas, the gear was getting too hot and that resulted in a gear that got a bit melted.

Of course, it could also just be that you were really hard on it and you need to just get a new gear now.

RC104ever wrote:Yeah, RTR isn't really 'RTR'. It just means that its been assembled but in reality you still need to check a few things and gear mesh is one of those things.

Another thing is the slipper clutch settings - it may have been too tight and so when your son was mashing the gas, the gear was getting too hot and that resulted in a gear that got a bit melted.

Of course, it could also just be that you were really hard on it and you need to just get a new gear now.

So slipper clutch is something I'm not familiar with at all. Any good guides for the b4.2's clutch other than the paragraph or two in the included instruction manual?

There's a way to test it that most guys at the track use, which I will vaguely describe here:

With the car and transmitter both on, and the transmitter in the right hand, set the base of the transmitter on the right rear tire (car facing away from you), hold the left tire with the left hand. Pull the throttle a bit, and the nose should rise a few inches. If it doesn't rise at all, the slipper is too loose. If it does a backflip, it's too tight.

Personally, I remove the slippers on my cars and replace them with an Exotek slipper removal piece. I don't like things slipping, diffs or otherwise, on my cars. If I can hear something slipping, it drives me nuts.


But yeh, my guess is the gear mesh was not set properly.

We replaced the eaten spur gear on my son's b4.2, and set the mesh with a strip of printer paper inserted between the gears.

When I run the motor, though, I am not certain that I like what I am hearing. I took a video to share the noise that I'm hearing.

[youtube]https://www.youtube.com/watch?v=mBrtDdBtyBw[/youtube]
[youtube]mBrtDdBtyBw[/youtube]

Any thoughts as to what that might be? The rest of the transmission spins smoothly.

The link is broken. Does it make any noise when you spin the spur gear with the pinion not meshed with the spur gear? If there is no clicking or occasional binding in the transmission when the spur is not in contact with the pinion, then the noise is likely from the pinion/spur.

clm wrote:The link is broken. Does it make any noise when you spin the spur gear with the pinion not meshed with the spur gear? If there is no clicking or occasional binding in the transmission when the spur is not in contact with the pinion, then the noise is likely from the pinion/spur.

Link broken? Bugger. Here's a direct link, as opposed to using the Youtube tag... https://www.youtube.com/watch?v=mBrtDdBtyBw

Anyhow, the noise went away after I backed the pinion away from the spur a hair. I guess the paper I used was a tad too thin?

I got better results taking a slip of receipt paper, folding it over once and inserting that between the gears to make the mesh.

After a while you can get a feeling of how tight it needs to be without using any paper, but it sounds like the spur might just have slight variances in runout.

The paper trick *usually* works, but after a while you just kinda know where it should be set. There should be a tiny bit of movement between the gears, just enough to show you that they aren't touching. Also, turn the spur to check all teeth, sometimes they aren't perfectly round, and you need to adjust your mesh to suit the spur gear.

It sounds like you've got the hang of it so far.