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  1. #1
    CB750 Member bmaher86's Avatar
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    Feb 2014
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    baton rouge, Louisiana
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    6

    Electric Starter Kickback? Starter Not Fully Engaging Problem

    Hey guys, So I'm building a cb750 and have got it running for the most part. Im sure I could find the problem myself but I figured why not ask the people of cb750.com first. That way I can avoid as much trial and error as possible. My 1981 cb750k starter is not fully engaging, its kicking out and grinding the teeth and not allow for the bike to start. I have solid battery, relay, regulator and solenoid. I just cleaned the stator with a clean rag and electrical cleaner. I even swapped the starters with a parts bike that came with the deal. Anyone have any ideas what could be causing the problem? Thanks Brandon.

  2. #2
    CB750 New Member jeffry's Avatar
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    Sep 2016
    Location
    southwestern connecticut
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    4
    Hi Brandon-- For the starter to not engage fully (and/or disengage in use) you probably have missing or broken "shims" (non-conductive plastic spacer-washers) on the rotor shaft. They disintegrate over time. There should be 5 or 6 (check your manual) on the base of the shaft to make the starter output gear engage w/the engine @ startup. If more than 1 or 2 are missing/broken, the starter's terminal drive gear won't extend far enough to engage/remain with the engine crank long enough for a start.

  3. #3
    CB750 Guru amc49's Avatar
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    Sep 2015
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    Fort Worth TX.
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    3,476
    I have no idea what that last guy is talking about and suspect he doesn't either.

    On that bike (DOHC '79-'83) the issue is well known, the starter itself has nothing to do with it.

    The starter clutch that starter drives has 3 rollers in it that have to all 3 catch and hold to lock the drive to turn engine, they often don't and slip making the crunch/grind. A one way lockup overrunning clutch there. There are 3 screws as well that hold the starter clutch together, they commonly loosen to do the same. If screws are loose then loctite them at tighten. Or, ding them with a punch to stake in place. If you are running car type oil with no zinc and friction modifiers that take the place of that zinc then the oil can be so slippery that the clutch rollers come loose as well. An oil change fixes that. The rollers are backed by springs that collapse and if all 3 are not close to same length then the 3 rollers cannot lock up at same time and again the problem. Any wear on one of the rollers and more of same.

    The clutch can only lock with all 3 of those assemblies working pretty much dead right, any one with less than a full lock and the other 2 pop loose and your noise.
    Last edited by amc49; 09-24-2016 at 12:53 PM.

  4. #4
    Moderator dirtdigger's Avatar
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    Feb 2012
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    Black Hawk SD
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    3,054
    The gears are always in constant mesh...there is no extending to engage like there is in the automotive starters. Its in the starter clutch as AMC mentioned.

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