Water pump question

3 replies to this topic
  • Derrick852

Posted May 28, 2009 - 05:01 AM


Hey guys, well, I just bought a used 01 yz 426, and the short of it all was just before I put the bike in the truck to take her on its first hard ride (after all my maintainace), while I was blasting around the sub division the water pump started pukeing coolant out of the relief port/hole. No big deal pulled the side cover off the bike and stripped the water pump. My question is how much play is normal in the water pump bearing/shaft? The bearing itself has no play either way in it, but the shaft does have a slight (maybe 10 - 20 thou at the most at the very end of the shaft (impeller end)when placed in the bearing) wobble. The shaft is not bent, and I took a micrometer to the shaft and it is not tapered so I did not buy a shaft/bearing. Just the seals. What do you guys think, what is the norm?

Being a two stroke rider my whole life, and the little bit that I have rode it, I LOVE this thing. That AP pump needs some tuning though, damn does the thing cough when you crack it off an idle.

  • grayracer513

Posted May 28, 2009 - 06:17 AM


The assembled water pump, sitting in the case only, is supported by one ball bearing. One ball bearing by itself has zero ability to hold a shaft on a given axis; it takes a minimum of two. So where is the second one?

With the crankcase cover back on the engine, the shaft plugs into a machined pocket in the end of the balancer shaft, and is supported by the bearing that supports that shaft. (see This Post) The only accurate check for excessive play at the impeller has to be made when the whole assembly is back on the engine.

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  • Derrick852

Posted May 28, 2009 - 01:27 PM


wow, you know your stuff man, thanks for the help! when i get home i will take a look at it.

  • Derrick852

Posted June 04, 2009 - 08:20 PM


two new seals and a bearing and she is good to rock!

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