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2003 Honda 400ex starting issue


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Hello! New to the forum and I have an issue with my project quad and I’d like to see if anyone here has any insight on how to narrow down the exact problem as I don’t have the money to just replace and test. I purchased the engine from someone and went ahead and replaced the top end with new pistons, rings, cylinder jug, and gaskets. It also has a hot cam so I don’t think the decompression valve is an issue. The quad turns over too slow (I think) to fire up which upon further inspection and research I discovered that the starter idler gear is supposed to free spin one way and not turn the other way, which it did not. So I took the stator cover off and messed with the starter clutch until it would freespin counter clockwise as it is supposed to, before it was acting like it was seized to the stator. After putting everything back together and turning it over I discovered that whenever the starter spins it locks back up again every time I fix it. Is this the one way clutch bearing, starter clutch, or something I am overlooking? Sorry for the long post I just feel like more info provided, the easier the diagnosis. Thanks for your time!

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Dream Car Giveaway

The one way  bearing is actually a sprag clutch. . It  should  lock to  allow the  starter  to turn  over the motor in one  direction  and free wheel  in the other.  This is  so  when  you start the  motor the  revs of the  motor  do  not feed back through the  gearing  and spin the  starter  to  destruction.

The starter  should  lock the  sprag  to  turn the  motor  over.  If it doesn't the  stater will  just spin free and nothing else happen. From  your description  the sprag is working properly.

If  it  seizes when  the  motor  starts  it will  spin the  starter as I  mentioned..  When  the  motor  is running  the  sprag  clutch is disengaged.  The  outer  part  spins with the  motor. the inner part  is where the  special   rollers  are  that  lock  the  clutch  when the  starter is spinning the  motor  over.

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Thanks for the reply! Just so I know we are on the same page because I’m not sure if I explained it as well as I could have. I would crank it over for just a second and take the stator cover back off to find that the starter clutch would no longer freespin counterclockwise, it would have a lot of resistance and turn the stator (and the crank) with it the same as spinning it clockwise. I then hold the stator in place and turn the starter clutch and eventually it will freespin again counterclockwise and turn the crank going clockwise (as it should I believe.) I put the cover back on and repeat with the same results every time.  

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I can't if that is  normal  or  not. It  may  be wearing a bit  and binding but the  only way I know  of  it  to  actually  have it start the  motor. When the  motor  starts the sprag  should immediately  release as the   motor speed exceeds that  of the  starter  gear train.  It's very possible it  is worn enough  to  bind  a bit when the  motor  doesn't start but  that hurts nothing as long as it  instantly releases  on motor starting.   The  special "rollers " in the  sprag  are  actually  either  a figure  8   shape or  could be  a  sort of  half round  shape  so  in the  one direction turned by the starter  they  twist  a  bit in their  slots  and  bind the   inner  and outer  parts together . . When  the  outer  part ( connected to the motor) spins  faster than the  inner,  those  rollers  lay  down  and release the  bind   between them.

There  are   tutorials on  Youtube   that explain  how a sprag works  much better than  I  can

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The  working of that sprag  should have nothing  to  do with the  speed the starter  turns the motor  over  unless it  was actually  slipping  when  it  should be  bound  tight.  If the  motor  is  slow to  turn  over  on the starter  it is  more likely  either a low battery ,  starter dragging  or  possibly just  tight   rings  in  the  new cylinders .Are  the   piston  and  ring  clearances  on spec?..  It's   possible  for  some binding there   if they   are too tight  in the  bore.

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