starting the teardown and got some questions

14 replies to this topic
  • gbalias

Posted April 26, 2007 - 07:15 PM

#1 i started tearing down my 1998 yz400 in search of my knocking noise and i got as far as getting the clutch taken out and what not.

i did notice that when i had the clutch plates/discs out, i was able to rotate the clutch basket ever so slightly left and right. it was enough to make a 'knocking' noise and i was wondering if a little clearance is normal?

im trying to check EVERYTHING while im pulling it apart so i can cover all the bases.

thanx guys.

  • grayracer513

Posted April 26, 2007 - 08:09 PM


Clearance between the primary drive gear and the driven gear on the back of the basket is normal. Clearance between the basket and the driven gear is not, and means the cushion unit is shot.

Be sure you check the condition and fit of that balancer gear key.

  • gbalias

Posted April 26, 2007 - 09:52 PM


hmmm....could you point those out in a diagram for me.....

im a bit confused.

and i definitely will check the balancer key.....thats what i was getting to before i had to leave for work.

  • grayracer513

Posted April 27, 2007 - 08:35 AM


The primary drive gear is the larger gear on the crank. The driven gear is the big one built onto the back of the basket. A little clearance between these two is normal and necessary.

Check for play between the driven gear and basket as shown on page 4-44 of the '99 manual.

  • gbalias

Posted April 27, 2007 - 11:23 AM


theres no play b/w the driven gear and basket. :applause:

im off to investigate the keyway and ill post what i find.

  • gbalias

Posted April 27, 2007 - 11:48 AM


how about rotational free play in the water pump impeller? ive got about 30-40deg of rotation before it meets any resistance on the counter balancer shaft. is that normal?

sorry for all the questions, but i want to be sure everything is all good in there.

  • gbalias

Posted April 27, 2007 - 01:12 PM


ok...heres a video of the counterbalance drive gear play:

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  • grayracer513

Posted April 27, 2007 - 01:14 PM


No, that would not be normal. The impeller drives by a flat tab on its end that slips into a socket in the end of the balancer shaft. A worn and/or loose balancer drive key could be the cause of that, but inspect the end of the shafts for where.

  • gbalias

Posted April 27, 2007 - 03:21 PM


it may be hard but, can you tell if the free play in the balance shaft drive is excessive? i posted the video in my last post.

heres the video of the impeller free-play:

  • grayracer513

Posted April 27, 2007 - 04:15 PM


That may not be excessive. You're looking at the cumulative clearance between 3-4 parts there. Open the crankcase cover and get a good look at the whole thing.

  • gbalias

Posted April 27, 2007 - 04:45 PM


do you mean to split the cases to expose the crankshaft?

ive already pulled this cover off to expose the counterbalance shaft/gear as well as the counterbalance shaft drive gear:
Posted Image

ive got #10 in this diagram already off.
Posted Image

  • grayracer513

Posted April 27, 2007 - 09:09 PM


Check the condition of #9 in this one:


  • gbalias

Posted April 27, 2007 - 11:39 PM


it seems ok to me....but i dunno how much tolerance it should have.

in your expierience does the movement in my video seem excessive?

i cant thank you enough gray....if you had a fuel meter, itd be overflowing.

  • grayracer513

Posted April 28, 2007 - 10:15 AM


It looks OK. You can examine the key and see if it's got any wear on it. They're cheap. If the drive gear nut was tight, it wasn't your noise.

  • gbalias

Posted April 28, 2007 - 03:31 PM


the key fits good. and theres really no visible wear.

i did, however, discover that the counterbalance shaft is worn inside where the impeller shaft inserts. i assume its supposed to be a slot shape but when i looked in there with a flashlight, its got a 'figure 8' shape to it. most likely leading to the large tolerance i observed while rotating the impeller by hand (video: ) i also noticed the coolant level was considerably low. im guessing with air in the system, the impeller wasnt always under drag from the fluid possibly helping in the premature wear of the slot.

im gonna be sure everything is full, check the noise and 1st replace the counterbalance shft and impeller shaft to at least have the peace of mind that those are frsh parts.

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