Just the other week I had my friend ride my 2003 CRF70 and that thing is always ol' reliable until this very day when the chain mysteriously broke while he was going a good 35 MPH and the case that holds the Auto Clutch simply busted into pieces and shattered part of the Magneto and well... Im not a big mechanic but I've heard people have actually ran into this exact problem but I've little to no clue on how to fix this, let me just show you some photos of the aftermath.



This is the Case and all the little pieces and a broken chain, (We threw everything out excpet the bolts that held the case on)




This was the best photo I could get but if you look closely towards my fingers you can see a bit of the Magneto and a big cut between the metal... I have no idea how much this is going cost to repair I know these are cheap fun bikes but honestly this doesn't look good.





Any feedback at all will be accepted.

as long as the cases arent cracked and are still holding oil you are probably ok. I am pretty sure the flywheel cover is interchangable from CRF50's so parts are cheap on ebay.

I am assuming it still runs?

could you try to get a better side shot of the counter sproket and the flywheel, it looks like your pickup is cracked off......

Dirtymutt9, on 22 May 2012 - 02:37 PM, said:

When you try to start it, you can hear the ignition comes up but seizes to keep running.

if you can try to get a side pic of the engine, you might have knocked your pick up off.


BTW the pickup is the little black box that is next to the flywheel......

Edited by Dirtymutt9, 22 May 2012 - 02:52 PM.

Things don't usually fail mysteriously.  There's normally an explanation or at least a couple of possibilities that you should check out before you go and do the same thing again, such as:
1.  Neglect/abuse.  Was the chain lubed frequently or did anything ever get stuck between the chain and sprockets and stretch the piss out of the chain?
2.  Was chain slack adjusted properly?
3.  Were the chain/sprockets aligned?
4.  Was the swingarm pivot bolt tight?  This will affect both 2 and 3 above.  Note that a loose swingarm bolt is a common problem on these bikes that leads to a wallowed out bolt hole.  The bolt needs to be checked religiously.
5.  Were the chain and sprockets being used beyond there expected life, i.e., worn to excess?
6.  Quality problem.  Pretty rare these days with modern manufacturing and quality control, but I stay away from stuff made in China if I can and will pay an extra $10-$20 if that's what it takes to get a quality part.
7.  Other.  I'm bound to be missing something.

You may not be able to tell if items 1-3 were a factor now that the chain is busted, but your maintenance practices (or lack of) should give you a clue.

Good luck and let us know what you find out so we all can learn.

MixingTheGoodStuff, on 22 May 2012 - 02:50 PM, said:

Could you describe this some more?  When I think of seizing, I think of it not running at all.

Punkinhead, on 23 May 2012 - 08:48 PM, said:

I have a good idea that he means this:

Quote

Edited by dirtbkr188, 24 May 2012 - 04:09 AM.

The pulse trigger mount is broken, you need another stator plate. You'll also need a flywheel puller tool to access the stator to remove it and swap the parts. That's as long as the wiring isn't torn or frayed.

As stated above, a little preventative maintenance can go a long way when it comes to these little bikes. Periodic chain lubing and adjustment usually prevents what happened to you.

dirtbkr188, on 24 May 2012 - 04:08 AM, said:

Yeah sorry haha

Punkinhead, on 23 May 2012 - 08:45 PM, said:

Well I adjusted the chain frequently and sprayed WD40 on it everyone now and then but I think something got stuck inside the chain like dirt and debris or something and caused it to stress and break. I understand about the tips above but I take descent care of my bike. I mean I wish I could live and breath just motorcycles but I have school and work that keeps me from my babies haha. As soon as I fix it im going sell it for like 400-500 bucks