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After further inspection it is the center gear, it is stripped. Is there any alternative for center gears other than the orignal part?

This one? That's rather bad
some-one spoke about a blackfoot 2 or boomerang spur, but I don't believe that will work

Kyosho had an option house 48p metric gear at one time, thorpe and robinson and im sure others had their stronger gears. Just a matter of what you can find today

Mr. ED wrote:
This one? That's rather bad
some-one spoke about a blackfoot 2 or boomerang spur, but I don't believe that will work

Yes that's the one. It does appear Thorpe has an aftermarket part.

there's one original in the bst section from rc10eh . paul's parts is the subject of the post

thorp and other companies did replacements, but generally are more expensive. I have bad experience with robinson racing replacements for this gear.

I put a thorp under drive kit for my optima and it worked great. I guess the question to ask is what cuased the gear to strip? That wear patern indictes that something was too loose (motor screws, bushings in the gars, the shaft that the gear sits on....).

My guess: too tightly meshed; making it heat up and become soft. You can also see the pinion wasn't well aligned: only the back half of the teeth is gone

I'd call that a classic motor loosening while running. At speed, the motor pulls away slightly and looses mesh, taking out the teeth, and as the motor winds up, the spur is still spinning and it doesn't take more than a sec to rotate around and round them all off....and yep, the pinion is in a bit too far.

jwscab wrote:I'd call that a classic motor loosening while running. At speed, the motor pulls away slightly and looses mesh, taking out the teeth, and as the motor winds up, the spur is still spinning and it doesn't take more than a sec to rotate around and round them all off....and yep, the pinion is in a bit too far.

Speaking of which, do any of you threadlock in your motors? I never have but perhaps it's a good idea...

highwayracer wrote:I put a thorp under drive kit for my optima and it worked great. I guess the question to ask is what cuased the gear to strip? That wear patern indictes that something was too loose (motor screws, bushings in the gars, the shaft that the gear sits on....).

Well the guy I bought this car off of must have neglected to put the plastic bushing in because it was no where to be found, which was fine while using my NIMH battery. Once I pumped so more power into it with an orion 7.4 lipo is when it decided to pop off and wedge itself stuck to the gear cover. This is what I get for being lazy and not checking it out to begin with.


Thanks for the bearing link Ed. Do you yourself us the original cluster gear?

The last time I ran with an original ultima gearbox I used my old faitfull clustergear of the ultima pro.
It's got a steel back-gear and the front plastic is a different kind; looks like machined POM. The teeth are 0.6mod.

From your description , what the previous owner forgot to put is a large enough sized washerbetween the O-ring and bearings. That washer is supposed to hold the gear in place, but if he used a smaller one ... well you saw what happens