Planet Minis

GlenRose

Hey, first post

got a chinese mid-bike given to me that ive been fixing. its a 50cc 4 stroke that looks like a CRF50 engine but with an electric start added and the kickstart removed. also has only one gear inside the crankcases plus a full auto clutch that i believe is exactly the same as the crf50 ones minus the shifter part.

heres a pic of it



but anyway the clutch seems to be engaging quite alot at idle, with the bike off the ground it spins the rear wheel quite fast (300rpm maybe) and i have to hold the wheel quite hard to stop it rotating at idle.

the clutch adjuster (the screw with the lock-nut) doesn't do anything to stop it. theres a bit less then 1 and a half turns of adjustment in that screw as well. not sure if thats correct or not.

compared to my zongshen 250 theres a ton of resistance when trying to rotate the output shaft with the engine off.

what could be wrong with it or do the centrifugal clutches on these just grab a little by their nature. do i need new clutch springs or are the rotating weighs buggered etc etc.

any help would be verrryyy appreciated! thank you!

mexicanyella

You didn't say anything about it, but maybe your idle speed could come down somewhat. I'm sure engagement speed varies from clutch to clutch to some degree, but my Z50 starts to grab somewhere between 2500 and 3000 rpm, and has locked in by 3500 or so. These speeds are well above the 1800-ish idle speed. Do you have access to one of those little digital tachometer/houmeters used on some mowing equipment? If not, just see if you can set the idle lower and get a reliable idle still.

And play with that adjustment some more. Can you tell if adjusting that screw makes any difference on the engagement rpm, or at least how abrupt the engagement is?

Also, if it's cold where you live and the bike is still running summer-weight oil, that can act draggy, at least until the oil warms up. I guess it isn't running any oil in the pic, though, huh?

I just asked yesterday in a different thread what was in those one-speed engines. You've answered part of my question. Thank you. Now please split the cases and take photos so I can see the rest.

doopsx3

yeah I gots a couple of those motors that I tore apart for the heads..not much inside there Mexicano Armarillo

GlenRose

haha yeah theres nothing inside them. aside from the crank shaft theres a pair of the splined gear shafts with just one set of gears in there. no circlip grooves machined for the other gears either. so it would be a fair job to put a proper gearbox in there. although it looks like the bearing pockets are machined. so maybe not so much work after all.

got some repsol sintetico oil in there for now just stripped the motor down out of pure curiosity there. ill have a look if i took any pics of inside the crankcase halves. i dont think i did though.

ill take some more when i pull it apart again to start modifying. heres the ones i did take - 4 stroke tear down pictures by glenscads - Photobucket

as for rpm it could be. but it sounds about right. ill borrow the mychron off the other bike and take a look to be sure.

thanks

mexicanyella

I just saw this on ebay, described as a clutch for automatic 70/90/110 motors. Looks like an inside-out minibike or go-kart clutch. Yours looks like a regular semi-auto clutch. Who can keep up with these Chinese engine engineers?

http://planetminis.com/attachments/2...autoclutch.jpg