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Old 10-14-2010, 04:27 PM
videomandw videomandw is offline
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Join Date: Jun 2010
Location: indiana
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Default Question On Drive Pinion Gear Problem


i have a question about the drive pinion gear on my chinese two stroke happy time motor. i am talking about the 1 inch gear coming off the crankshaft that drives the large clutch gear on the right side (as you face front) of the bike.

this is the second time it has sheared the little woodruff key that attaches it to the crankshaft. when i went to put the pinion back on the end of the crank, i noticed it was a sloppy fit. the gear wobbled slightly on the crank and even with the big screw tightened all the way, i could pull the gear back and forth on the shaft about an 1/8 of an inch. in other words, it did not fit snugly onto the end of the crank even with the large slotted screw tightened all the way with the lock washer on it.

here are my questions:
1. did i either ream out the inside of the pinion or the outside diameter of the shaft? i shut the engine off as soon as the woodruff key sheared. if i reduced the diameter of the end of the crank, does that mean i need a whole new crank and what does that involve?

2. am i missing a washer or something to keep the pinion from sliding back and forth on the end of the crankshaft?

3. where should i get replacement woodruff keys that are hard enough not to keep shearing off? i bought the last one that sheared at my local ace hardware and ground it down to size to fit the slot.

i don't want to keep replacing keys every 100 miles or so; i want to fix that pinion problem right. otherwise my motor and bike perform like a dream.

thanks in advance for any and all advice,

valparaiso, in
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Old 10-14-2010, 07:42 PM
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killercanuck killercanuck is offline
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Join Date: Dec 2009
Location: Wallaceburg ON
Posts: 1,752
Default Re: Question On Drive Pinion Gear Problem

wow, that little gear shouldn't have any play at all. Chock that up to chinese presicion. Depending on its orientation, you should add a washer where you see fit to help lock it down. You don't want is sticking out too far, so I'd suggest washers under the lock screw, with blue lock-tite and use an impact driver(if available) to snug'r down good.

Your key's are probably shearing due to the slop in the current configuration. Any 'stronger' key would do the same under the circumstances. Having it torque'd down good with a washer or two should stop the shearing.

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Old 10-14-2010, 10:10 PM
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corgi1 corgi1 is offline
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Join Date: Aug 2009
Location: KCMO
Posts: 2,282
Default Re: Question On Drive Pinion Gear Problem

If it woobles it is not right,too much play,,,if after looking carefully at the crank for wear ,if it looks smooth ,you might order another small gear and try it,,I believe ti should be almost a press fit and the sloted screw a safty ,,,also carefully looking on the inside of the small gear probibly in the key way area ,is it cracked and stretched open
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