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Motorized Bicycle Trouble Shooting Use this area to post problems that may arise, if you could use some help in figuring out what is wrong with your engine and what needs to be done to achieve top performance.

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Old 10-19-2016, 08:46 PM
crassius crassius is offline
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Default on the current problem with woodruff keys

Just had a guy come it with free spinning drive sprocket. Been seeing a lot of these on the boards lately, but none at my shop. I don't know what kit it is, but it has a gold sticker on mag cover saying 'not for road use' according to EPA.

Went to put a key in, and found why it was bad. All motors I've seen always had all four keys matching in thickness (either fat keys or thin keys). This motor has slots cut for fat keys, but all attaching parts had slots cut for thin keys. This lets the key fall out or even turn a bit sideways and get sheared off.

To keep repair cost down, I used a bit of steel in the slot to hold a thin key a bit higher and tightened it down well. Looks solid now, but will re-post if it fails at some point over next couple weeks.
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Last edited by crassius; 10-19-2016 at 08:49 PM.
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Old 10-20-2016, 04:46 AM
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ZipTie ZipTie is offline
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Default Re: on the current problem with woodruff keys

Another example of amazing Chinese quality control. They just use what is laying around to assemble their engines to fill their orders. I wonder how they sleep at night knowing that all those motors are going to fail to move sooner than later. It's a good simple fix idea crassius . Yep I've read a few stores of oddly loose woodruff keys too. I still laugh in amazement at the story of a guy finding a ciggy butt in his piston chamber.

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Old 10-20-2016, 02:35 PM
crassius crassius is offline
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Default Re: on the current problem with woodruff keys

This may be due to the flat toothed drive sprockets that bunch up the 415H chains being replaced by pointy toothed sprockets. Perhaps all flat toothed sprockets are wide key, while all pointy toothed sprockets are narrow key.

I don't have enough old spares here to be sure.
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