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Discussion in 'Motorized Tandems, Trikes and Recumbent Bicycles' started by Fulltimer, Jun 23, 2013.
Digging into the distant memory banks of youth I recall that we used different springs to adjust the rpm that the shoes grabbed. A lot of the lads that were more avid go karters than I was had a small box with different coloured springs. Each colour denoted the strength of the spring.
You may have weaker springs in your clutch and it is engaging at an idle. Not a guarantee but worth a look.
Thanks, I'll check that out.
If you remove the auto clutch cover and roll the bike back and forth can you watch the clutch hub turn independently of the clutch drum?
Drum is stuck to the hub?
Broken friction shoe spring?
With the clutch pulled in everything moves. Except the bike.
I am guessing that you are using the auto clutch for the China Girl engine as shown in your pictures. If the "starter spring" is non-existent, the auto clutch's hub should not turn when the engine is off as it is attached to the engine's crank shaft. If you roll the bike back and forth with the hand clutch engaged (hand lever out) the clutch drum should turn leaving the clutch hub stationary. If the hub and drum turn as a unit then the drum is somehow jammed or stuck to the hub.
Note: most auto clutches do have a "starter spring" that is supposed to allow pedal starting of the engine. It acts like a one way clutch device, allowing the auto clutch and hub turn in unison to start the engine. Once the engine is started the "starter spring" releases it's grip in the clutch hub and the auto clutch goes into the normal, as expected mode of operation.
This can be observed when watching the auto clutch (engine off and cover removed) and rolling the bike back and forth. Rolling forward the auto clutch will be locked up and turn as a unit. Rolling backwards the auto clutch drum only will turn and the hub will be stationary. If the "starter spring" is installed backwards then the reverse of the above description will be true. The clutch will be locked up and turn as a unit when rolling backwards, but the drum only will turn when rolling forward.
Also when the engine is running with a backwards installed "starter spring" this will cause an unwanted drag on the auto clutch and the bike will want to roll under engine power at all times, even at idle speeds. Note that this effect is not strong enough to propel you down the road so when the bicycle is at a complete stop the engine will stall while at idle speeds when you release the hand clutch. The "starter spring's" grip is not as strong as a fully locked auto clutch in drive mode.
Also... if this "starter spring" is installed backwards then the only way you will be able to start the engine is by using the pull starter. Once the engine starts the backwards installed starter spring will create the above described issues leading to headache, annoyance and foul language.
GearNut: "If you roll the bike back and forth with the hand clutch engaged (hand lever out) the clutch drum should turn leaving the clutch hub stationary. If the hub and drum turn as a unit then the drum is somehow jammed or stuck to the hub."
You hit the nail on the head. With the clutch engaged everything turns. Inside the clutch hub is a cup with bearings in it. I checked them and they seem to be fine. By that I mean they are all there, all 5 of them, and they move freely.
It seems that you can't get individual parts for these things and I can get a new centrifugal clutch for around $35.00. Maybe I should go that route?
Before buying another clutch I recommend you do a total tear down of the clutch you have and inspect it for abnormalities.
Is the drum egg shaped, causing drag on the friction shoes? (possibly repairable)
Is the drum welded to the hub off center? (difficult to repair)
Was the crankshaft extension machined too short? (possibly repairable)
This would cause the friction shoe's hub to be compressed against the drum's hub when the center bolt is tightened properly. The whole clutch assembly will be a friction locked "sandwich".
Was the drum hub machined too long? This would cause the same compression issue as a crankshaft extension that is too short. (and my best guess as to the repair needed).
The crankshaft extension needs to fit into the drum's hub far enough to support it and allow a teeny (about 0.020") bit of in and out free movement of the clutch drum hub when the whole assembly is bolted up tight.
There is no play in the clutch drum that I can tell. Everything else you listed seems to be okay. When I parked the bike, to turn it into a trike, it worked fine. The clutch drum has a little wobble to it but that doesn't seem to have any effect on it. It was that way before.
It sounds like you are saying that while the engine is turned off the clutch hub/ friction shoes are disconnected from the drum as they should be.
Am I wrong here? I thought that you said previously that it was locked up...
All I can come up with now is...
When the engine is at idle the shoes are expanding prematurely at too low of an RPM and locked to the drum. A weak or broken shoe spring is all that I can think of that would cause this.
You could try a new spring if you can find one or as you stated before, just get a new clutch.
So far, if I am understanding you correctly, your current clutch passes all of the static tests so I am at a loss as to suggesting a repair.
I was looking at that spring. It isn't broken but it may be bad. In answer to your question about the shoes. Yes, when the engine is off they don't touch the drum. I tried idling down the engine to see if that would help. It didn't. The problem in finding a replacement set of springs, there are 2, would be finding the right tension.
Thanks for all your help. I appreciate it. It probably would have helped if I had used the correct terminology. I think I'll just go ahead and order a new clutch.
Pirate Cycles had the centrifugal clutch for $30.00. But they were out of them. I ended up ordering 1 from JNMotors for $34.95 + $20.00 for shipping. Shipping really ran up the price! Well, it will be here this Friday. But I'm going camping Friday and won't be back until Monday. So maybe Tuesday I'll have an update.
It doesn't fit! My shaft is too big around for it. Back to the drawing board I guess.
There was an insert in it. Apparently so it would fit a smaller shaft. I took out the insert and it fits just right. BUT...the bike still will not set at idle without the bike wanting to take off. That, of course, stalls the motor.