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Discussion Starter · #1 ·
Hi all!

I have an orion rxb150 with the YX150 motor. It seems that my first gear is on its way out. Under heavy load (hill climbing, pulling up for a wheelie, etc) I get the skipping sensation, as if my chain is skipping a tooth. This obviously isn't the case, so I am assuming I will need to split the cases to rectify this.

I have found what I think will fix my issue from T bolt: GPX / YX / ZS H-D 4up Transmission (150cc - 160cc) - TRC-3001 - Parts & Kits ZS 155cc & YX150/160 - Pit Bike Engine Parts - TBolt USA, LLC

I am a bit nervous when it comes to splitting the cases. I've rebuilt plenty of top ends before, replacing vales and piston, etc. But I've never ventured into a gearbox rebuild. Seems like there's plenty on youtube videos (however none specific to the YX150) that I can follow and figure my way out through this. I'm confident in my technical ability but I am used to following some sort of guide, be it a writeup, video, or shop manual. Does anyone know of any resources that can help me out? Or anyone familiar enough with these engines that could give me some advice? Anyone know what flywheel puller I will need, and if I'll need any other specialty tools or pullers?

I'd like to try my hand at rebuilding it with the $150 gear set before I shell out close to 1k for a replacement YX. Any help is appreciated! Thanks everybody!
 

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Discussion Starter · #4 ·
I was able to replace both transmission shafts and the selector drum without issue, but I'm still getting "skipping" in first gear. My old gears and drum looked fine upon inspection, and I didn't find any obvious damage anywhere in the case.

What else should I be looking at now? Shift shaft assembly? detent? I'm at a loss for what could be causing this without showing any damage in the case
 

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You might want to go over the chain and sprockets again, checking for a stretched chain and worn sprockets. Also, does the rear wheel have the rubber dampers (part #2, shown below) in the hub? They wear out and will give a "skipping" feeling under a load.

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Maybe check the teeth on the primary gears under the clutch cover...but I think that would affect every gear.

Did you only change the shafts, or gears too.
If the cogs, on the sides of the gears, are worn or broke...or the holes that they mesh into...that would cause a skip under load too.

Are you sure it's not the clutch slipping?
 

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Discussion Starter · #7 ·
You might want to go over the chain and sprockets again, checking for a stretched chain and worn sprockets. Also, does the rear wheel have the rubber dampers (part #2, shown below) in the hub? They wear out and will give a "skipping" feeling under a load.

View attachment 278773
My rear wheel doesn't have cush drive, the sprocket bolts directly to the hub. My chain and sprockets seem fine, in fact they were the first thing I changed when I started down this rabbit hole. I also get the same behavior with both of my wheel sets (I have a dirt set and a 14" sumo set), making me think that end of the drivetrain isn't where my issue lies.


Maybe check the teeth on the primary gears under the clutch cover...but I think that would affect every gear.

Did you only change the shafts, or gears too.
If the cogs, on the sides of the gears, are worn or broke...or the holes that they mesh into...that would cause a skip under load too.

Are you sure it's not the clutch slipping?
I used this set from t-bolt: GPX / YX / ZS H-D 4up Transmission (150cc - 160cc) - TRC-3001 - Parts & Kits ZS 155cc & YX150/160 - Pit Bike Engine Parts - TBolt USA, LLC
Everything after the clutch has been replaced, and I didn't see any damage on my old gears or dogs when I took them out. everything under the clutch looked good too. I was looking real hard for some chewed up gears / other damage somewhere in there, and couldn't find anything out of the ordinary. I'm fairly certain it's not the clutch slipping, the skip feels very jarring (think "clack, clack, clack) and not a smooth loss/onset of power like a clutch letting go. My clutch plates also looked fine to me, though I didn't set them under a microscope.

I really appreciate the suggestions guys. I'm truly baffled at this..
 

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How about the primary gears...19 and 21?
There is also...rubber "cush" inside of the big primary gear that can wear out...altho it must take a lot to wear them out. Maybe 150cc could do it :)


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Discussion Starter · #9 ·
How about the primary gears...19 and 21?
There is also...rubber "cush" inside of the big primary gear that can wear out...altho it must take a lot to wear them out. Maybe 150cc could do it :)


View attachment 278774
I didn't take any photos of those gears in particular, though i didn't notice any obvious issues when disassembling. After looking at the pictures I do have, I do notice something that looks like it could be suspect, which I put a red circle around in the pic. Thoughts?
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I think your red circled gear(s) only affect kick-starting. But what I notice is the one odd gap between the clutch discs. If you pull the clutch cover, and that odd gap is still there, THAT could be a problem.
 

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Discussion Starter · #11 ·
I think your red circled gear(s) only affect kick-starting. But what I notice is the one odd gap between the clutch discs. If you pull the clutch cover, and that odd gap is still there, THAT could be a problem.
I believe the gap is there because I had the springs/bolts removed, so the plates were loose before I removed the basket (maybe I should pull the cover off again for another inspection?). Upon reassembly they looked right to me, and seems to operate normally
 

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Discussion Starter · #12 ·
Turns out my issue WAS caused by the chain. Specifically, the chain tension. When the rear compresses it dramatically alters the length between the drive sprocket and the hub sprocket, effectively loosening the chain by alot. I can't believe I didn't realize this before and split my cases for nothing. To test this I tightened my chain a lot (to the point where it's too tight now) and the skipping vanished. I have a shock extender on the way to hopefully help enough that I can loosen my chain some. If that doesn't work, I'll be looking at DNM rear shocks. I'm on my way to wheelie heaven now! Thank you to everyone who replied, and yes, I feel very stupid now.
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