Clutch Drive Gear Nut

[the fitz blitz]

Thanks in advance for any help.

I was bombing along on my 80cc 2 Stroke bicycle conversion & the rear wheel locked up. Restarted and it happened again. I could tell she was not happy.

Thought it was a seized piston but with my limited knowledge I felt problem was in the clutch/gear area as motor would start easy after a while without requiring me to free piston. And locking would happen after engaging drive.

Upon inspecting Clutch Drive Gear Nut

http://motoredbikes.com/media/54-remove-clutch-drive-gear-nut.39510/#media

I can see that it is damaged with a tooth missing and some scaring upon the clutch wheel cog. When I tighten the Drive Nut the bike will run a short distance then will become loose losing drive and rattling.

So my question is - is it a big problem. Would replacing the nut be of help or is the problem of greater magnitude - I bow to your expertise.

Background - I have had bike about a year. I ran in carefully. For the past 4 months I have ridden 3 times a week 10 km twice a day on fairy bouncy surface (Irish roads) I go through a speed camera and it flashes me at 60 kph (that's my girl) and I go 50-55 kph all journey. I always put plenty of oil in mix and the heat is not an issue ! I weight 240 pound (I think, I'm not sure US Measures) - maybe that's an issue with the drive gear and its just worn out (I don't need anybody to tell me to give up the pork pies - ok)

Thanks again

 

[the fitz blitz]

Image 1. This how far the nut is/was out & damage. Image 2. Damage to clutch cog. Image 3. Ridge at rear (Maybe is normal). Image 4. I forced nut further in by tapping with hammer and er..........it split.

 

[crassius]

happens sometimes when factory isn't careful about installing that small bevel gear

when replacing it with a new one, be sure threads inside crank are good, tapered area where gear sits on outside of crank is good, and slot and woodruff key are good - when you put it on, be sure it is sitting straight on the taper (spin the rear wheel with plug out so you can watch for wobble as it turns) and gently tap it straight if it wobbles - finish tightening with a hand impact driver

when done, be sure to clean out that broken tooth and all other debris

 

[the fitz blitz]

thanks - no woodruff key - must have lost it - actually thinking about it i saw something tiny catch my eye fall when opening the case (of course being small it can't be important - bloody hell) but you have pointed me in right direction. I will search physically and on net for woodruff key solution and there are a few threads on here helping me. i don't know any terminology so thanks again.

 

[Frankenstein]

Ohhh OK now this is how my last crankshaft took a dive bomb. I let it be loose and the gear shredded my Woodruff key which mixed with grease to make a grinding paste, the shaft was completely ruined on the taper, no holding a gear after that.

Now here's the fun part, sometimes after smacking that gear onto the shaft, the inner flat of the gear sits lower than the highest point of that crank arm. What that means is it doesn't matter how tight you drive the bolt down onto the gear, because it's actually getting tight on the crank alone, not the actual gear.

A seller on eBay happened to show me a solution, he has a small copper washer, almost shim-like, it sits outside the diameter of the shaft but inside the raised parts of the gear. So you drop it in, filling the void and allows good torque where it matters, just put the original lock washer on top, and then tighten the bolt.

Additionally I would replace that flathead screw style bolt with a 14 mm headed bolt, can't remember the thread but at least one other nut is 14 as well which is nice to have some consistency (especially as you get older) when working on the various fasteners on the engine.

Bicycle_motor_works on eBay sent me the washers, you might be able to find something at a hardware store that will be exact but I doubt it. In a pinch on the side of the road I cut up a key ring, and bent it smaller into a circle to fit that shape nearly perfect, worked till I got home even though the damage was pretty much done.

 

[Frankenstein]

Oh and Woodruff keys can be found at Lowe's, maybe home depot, and also harbor freight. Get them from that guy I mentioned and he could probably throw in a washer if you ask him while ordering. It's a good idea to have a couple spare keys around. Good luck

 

[Frankenstein]

And I missed the part where your gear split, he sells them too. You'll have to replace it and splitting it may be the actual problem anyway, it could have had a Crack that slowly grew and finally it was too much and it just refused to stay on, and it's possible the Woodruff hey was completely destroyed, it would be no simple task for it to fall out with a gear in place, but to slip under the gear outside it's little groove, wedging the inner part of the gear out could help that little crack's stress riser to unzip it's way right up through the rest of the gear.

 

[hmbab2000]

I'm battling battling this same issue!
Mine didn't fail, but it looks close.
I can't get the small gear to seat, but then I don't have a working bolt. The tip got trashed. Through reading this, I just need to use the bolt to tighten it back down?

 

[hmbab2000]

Here's the amount of "damage" that happened.
I got lucky when I thought I was hearing things!

 

[Frankenstein]

The back of the gears should be flush, almost always some of the bevel gear will be higher. Hammer it on with firm but gental smacks, if it truly won't set on there after hammering then it's probably damaged beyond help. Hopefully a new gear does it, if not then it's the crankshaft that needs replacing...