Motovox MBX 10 engine shaft problem

#1
1st post here. Just got a used Motovox MBX 10 minibike and was going though it before letting my son ride it. Removed the clutch assembly because i found some slop in the fit of the clutch key/key fit. After removing the clutch, the shaft if broken where the key sits in the shaft. What are the easiest/best options for repair. I'm not an engine guy but I am an Industrial Maintenance tech and work on equipment.
 

Motra

Active Member
#2
A new crankshaft is really the best way to fix it but those engines aren't worth throwing any money at. An upgraded engine is probably the way to go. Most here will tell you to install a Harbor Freight Predator.
 
#3
Thanks Motra. I was afraid of that. I got this minibike for my 8 yr old so I wasn't really worried about lots of power. He rode it for about and hour with no issues. I have access to a machine shop at work that could cut a new key slot on the other side of the shaft. Is it hard to remove the shaft and put back in?? I'm not an engine guy. I am mechanical just not engine wise. Is there any guides or directions I can follow? I hate to just dive right in to the guts of this motor. This is just new ground for me.

I can handle 480 volts all day long though.. I believe I could do it and really want to learn the ins and outs of these small motors. I'm going price the motor you mentioned. I have $190 invested so far..

Will the 3hp Predator engine work ok? My son is only 8 yrs old so that might be a better choice for me (and his mom).
 
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#4
I would personally just up the ante & buy the 212 predator. IIRC, they have a throttle stop screw so you can control how far he can open the throttle.

Just my opinion, but unless there's really a serious constraint, it's worth the extra $10 to get the 212 over the 99cc unit.
 
#5
ive been reading alot of people saying the throttle stop thing but ive noticed i i hold it half throttle it can still clomb rpms mabye just because i remived some parts
 
#6
If it was me...what I would do is clean the rust off the shaft good and then mig the broken part of the shaft a little at a time as to not heat up crankshaft and melt bearing seal an then grind the welded area back to specs with a flapper on a grinder and rework the slot with a dremel just be carefull not to add too much material....just my two cents and others may warn against but it is a cheap engine...nothing ventured...nothing gained! :thumbsup:
 
#7
Thanks Boomstick! Which Predator engine do you recommend? There are three 212 engines on the Harbor Freight site. Item#69727 or Item#69730 or Item#60363

I'm still learning all of this minibike stuff.

Sounds like the stop screw will work great. Will I have to get a different centrifugal clutch or is the shaft the same size?? Sorry to ask such simple questions. You guys could do this in your sleep. I need all the help and advice I can get. Better to ask and not get the wrong motor..
 
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#8
No problem. Either way, any of the Predators will do what you want. Part number #60363 IIRC is the Hemi version, with a little bit of extra oomph.

All of them will tote you around well enough, and there's zillions of aftermarket out there for them & the other clones.

You'll likely need to buy a 3/4'' centrifugal clutch, they're not terribly expensive.


All the throttle stop does is keep Jr. from cracking the throttle all the way open. All it does is limit engine speed.
 
#9
jdogg, I thought of that but was worried of heat also. The shaft piece that broke seemed to be hardened. I wonder why it broke like that. Any thoughts on why it broke? Is that common? Thanks for all the input. My son and I spent all day working on the "new" minibike. He is so excited about it all.

I had other issues with the motor. We just got the minibike yesterday, It would only run when the choke was on. We went and got a new spark plug (automate 255). We drained the carb and gas tank. Went and got some 100% gas and after the motor got good and warm it ran fine. He rode it for about and hour but then it started dying and now it won't run good at all. I wonder if this motor has internal problem related to the shaft piece breaking??
 
#10
No problem. Either way, any of the Predators will do what you want. Part number #60363 IIRC is the Hemi version, with a little bit of extra oomph.

All of them will tote you around well enough, and there's zillions of aftermarket out there for them & the other clones.

You'll likely need to buy a 3/4'' centrifugal clutch, they're not terribly expensive.


All the throttle stop does is keep Jr. from cracking the throttle all the way open. All it does is limit engine speed.
Thanks Boomstick! We have a Harbor Freight about 30 minutes from me. I also live close to a Northern Tool. Do they have a motor that is any better?
 
#14
Just go to Harbor freight, everything's cheaper there, & it seems like the stuff is still the same quality.

A predator is a predator is a predator. lol.
 
#15
I got a used 97cc that had a broken PTO like that welded up. Seemed to be a good fix, no problem with it.

It's some work to remove the crankshaft, but I would take it out if it needed to be welded up, then keyway cut.
 
#18
I got a used 97cc that had a broken PTO like that welded up. Seemed to be a good fix, no problem with it.

It's some work to remove the crankshaft, but I would take it out if it needed to be welded up, then keyway cut.
I thought about this. Mine seems to be holding up for now. Just lugging my 7 1/2 yr old around the yard for now. He's still kinda scared.
 
#19
Lol.. Gonna check on it next payday. Any heat issues/muffler clearance with kids legs with a 6.5 motor on the Motovox??


Thanks for the help Guys!!
Not sure about the stock clearance but if you go the header route you will need a jet kit, free flow filter and filter adater and carb stud

Motovox 10/11/12 Under Seat Header

Re-Jet Kit for Stock 6.5hp Carb

K&N Style Air Filter Kit

109mm Carb Stud

Not exactly the info you wanted....just thought I'd throw it out there!! Adds up quick!! :scared:
 
#20
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