Screw came off from small bevel gear

U

userix

New Member
I started to heard weird clanking sound from the clutch area that seems random. I decided to open it up and check and I found that the small bevel gear screw came off and was grinding away the clutch cover. The bike still rides fine, but is it safe to continue riding without that screw? Will the gear come off eventually? The screw looks weird and nothing like the one pictured on pistonbikes. It won't even go back in anymore. I guess it got messed up from the gear spinning. I assume I need parts number #3 and #4 from the diagram found at pistonbikes:

Crankcase
 

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userix said:
I started to hear weird clanking sound from the clutch area that seems random. I decided to open it up and check and I found that the small bevel gear screw came off and was grinding away the clutch cover. The bike still rides fine, but is it safe to continue riding without that screw? Will the gear come off eventually? The screw looks weird and nothing like the one pictured on pistonbikes. It won't even go back in anymore. I guess it got messed up from the gear spinning. I assume I need parts number #3 and #4 from the diagram found at pistonbikes:

Crankcase
Click to expand...
I have seen that happen a few times, even seen the gear make a hole in the clutch cover......lol The rider was listening to an iPod and didn't hear the noise LOL
Your screw has had the threads ground off.
Do not try and put it back in as you will damage the threads in the crank.

If you keep riding it you risk the gear coming off and damaging it as well as the
clutch gear and the cover or worse.

Then you will really be screwed! lol

To put it back on properly you will need a impact driver that you hit with a hammer
to tighten that screw.

After hearing noises how long did you wait to check it out?
 
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I started noticing it yesterday afternoon when I rode for 3hrs. I live by bikeguy joe's signature quote "If it ain't broke, and you mess with it long enough, it will be."

But today when I rode it this afternoon, it sounded like something was loose and flying around in the clutch case. So I finally decided to open it up to take a look and thank god I did. Is that round piece of metal I am holding in the 2nd pic the remains of the spring gasket?
 
You are correct. You need a new screw (#3) and the star lock washer (#4, what they want to call a spring gasket) that fits in between the head of the screw and the gear.

Part numbers 10 and 11 in bicycle-engines.com parts list.
Clutch Assembly

Also, in the second pic that you posted I noticed that the lock screw for the flower nut in the center of your clutch is missing as well.
Bicycle-Engines.com lists it in the text as part #1a, but they do not show it in the diagram or in the for sale list. (?)
 
GearNut said:
You are correct. You need a new screw (#3) and the star lock washer (#4, what they want to call a spring gasket) that fits in between the head of the screw and the gear.

Part numbers 10 and 11 in bicycle-engines.com parts list.
Clutch Assembly

Also, in the second pic that you posted I noticed that the lock screw for the flower nut in the center of your clutch is missing as well.
Bicycle-Engines.com lists it in the text as part #1a, but they do not show it in the diagram or in the for sale list. (?)
Click to expand...

Good eye. It's there, just in another slot and out of the pic's view. Thanks for noticing though.
 
MotorBicycleRacing said:
To put it back on properly you will need a impact driver that you hit with a hammer
to tighten that screw.
Click to expand...

This is a very bad idea. There's a good chance you could hurt the crank by hammering on it.

I suggest just using a big screwdriver instead. You can lock the gear by either jamming another screwdriver in the teeth, or use something like a piece of brass. When you put it back on it doesn't have to be break wind tight, that's why it's there's just a slot screw head on the bolt. I found the lock washers at a hardware store.
 
I just stick a penney in the gears to jam them.

I don't think you will harm the crank by using a hammer impact. I have driven the gears on several engines with a deepwell socket and a hammer.

Please explain how and what damage could be caused by using hammer to hit a driver or socket on the gear.
The gear is press fit. you won't get it on very far without use of a hammer . The screw is not there to pull the gear down. It is just there to hold the gear on after it is pressed or driven flush or nearly flush with the clutch gear
 
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wayne z said:
I just stick a penney in the gears to jam them.

I don't think you will harm the crank by using a hammer impact. I have driven the gears on several engines with a deepwell socket and a hammer.

Please explain how and what damage could be caused by using hammer to hit a driver or socket on the gear.
The gear is press fit. you won't get it on very far without use of a hammer . The screw is not there to pull the gear down. It is just there to hold the gear on after it is pressed or driven flush or nearly flush with the clutch gear
Click to expand...

Well, there's a good chance you can knock the flywheels out of true by hammering on the end of the crank, and it's not necessary.

With a little ingenuity you can use the puller tool that removes the pinion gear, to press the gear on. No hammering is necessary.
 
biknut said:
Well, there's a good chance you can knock the flywheels out of true by hammering on the end of the crank, and it's not necessary.

With a little ingenuity you can use the puller tool that removes the pinion gear, to press the gear on. No hammering is necessary.
Click to expand...
The impact tool allows you to easily tighten or loosen that
straight slotted screw for the bevel gear without holding the gears or
jamming anything.

By hammer I mean you tap it not that hard, done it many times with no problems.
Just need to turn that straight slotted screw that is very easy
to strip out. the impact drivers come with hardened straight and philips
bits that do not slip.

To remove the gear you use the puller of course and the gear does not
need to be hammered to install.

biknut, you have experience on maybe 2 or 3 motors if that.
I have had over 500 motors that I have given a warranty on........
 
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MotorBicycleRacing said:
The impact tool allows you to easily tighten or loosen that
straight slotted screw for the bevel gear without holding the gears or
jamming anything.

By hammer I mean you tap it not that hard, done it many times with no problems.
Just need to turn that straight slotted screw that is very easy
to strip out. the impact drivers come with hardened straight and philips
bits that do not slip.

To remove the gear you use the puller of course and the gear does not
need to be hammered to install.

biknut, you have experience on maybe 2 or 3 motors if that.
I have had over 500 motors that I have given a warranty on........
Click to expand...

It's true I only know very little about China Girls, but I bought my first impact driver in 1969.

My forte is more about destruction lol.
 
Cool, so the use of impact driver won't hurt my crankshaft? I have an impact driver somewhere in my garage. I'll dig it out once I get the replacement parts.
 
A little off topic, but the same thing happened to me and I reaaallly don't want to pay $13 with shipping for that screw, would it be possible to just get something with the same thread size, cut it and use a washer to hold the little gasket on?
 
Yes. So long as it does not come in contact with the inside of the gear case cover.
Exactly what "little gasket" are you referring to?
 
I'm not really sure what to call it... I think it's the little piece of metal that is shredded in the pictures at the beginning of this thread. It's a little serrated metal ring. And does anyone happen to know what size the bolt is? I was think 6mm but any specific numbers would be awesome. Thanks!
 
Awww now you got me to go out to the garage and dig out my tap and die set. :p

It is an M8x1.0 bolt

The shredded part was an internal toothed lockwasher.

Here's some cheap parts and a diagram:
Crank & Piston

Parts #3 and #4 are the ones.
 
you will need to chase the threads on the crank with a metric tap. from the looks of the crank screw you probably did some damage to the threads in the crank, using a hammer impact wrench won't hurt the crank. Just a few good taps on the wrench some loctite( blue loctite) on the threads won't hurt either.
to lock the gears use a rag to jam the gears.
 
Glad I found this thread as it's great to get some guidance from those who've experienced this before.

This just happened to my bike. I heard a scratching sound... kind of like a chirp every few seconds. Fortunately, I was close to my house...pulled off the cover and out popped the screw. The first two threads were worn/gone...and just a little wear inside of the cover.

I ran an new bolt into the crank threads to true it up...there wasn't much damage, but it did have a little resistance as it went in...somewhat concerning, but it feels solid now. I was able to salvage the original screw with a die, and then used some loctite as I screwed it back on.

I didn't hit it with an impact hammer...but I suppose I could? We'll see how this holds. If it comes out again, I'm not sure I can save the crank threads...maybe a retap there would still work. Let's hope it doesn't come to that.
 
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