Repeat failures of water pump seals

When I had a leak spring up in a water pump that I had just resealed a couple of rides ago, I decided to investigate.

The impeller shaft has only one single row ball bearing on it. In order to hold a shaft on a single axis, you need a minimum of two. To address this, Yamaha inserts the impeller shaft into a machined pocket in the end of the balancer shaft so that that shaft supports the impeller shaft as well as driving it. The right side balancer shaft bearing then, becomes the second bearing on the impeller shaft, and the shaft is held on axis over its length as it rotates.

But here, I had a new shaft and seal already leaking. Something wasn't right. On inspection, I discovered that the right side balancer shaft bearing had a considerable excess of clearance. Measured with a dial indicator, it was over .015", clearly indicating a failed bearing. Because of the shaft lengths involved, .015" at the drive end of the impeller shaft would be exaggerated to around .020" or more at the seal, and since the balancer shaft is deliberately out of balance, it would necessarily force the drive end of the impeller shaft off axis as it spun, and the seal would have to try to follow that oscillation.

There is good news and bad news. The good news is that the balancer shaft bearings in the '06+ Gen2 engine can be replaced with the crankcases assembled and in the frame simply by removing both crankcase covers, removing the drive gears, counterweights, and bearing retainers, and driving the shaft out one side from the other. This needs to be done skillfully to avoid damage to the shaft, and it is important to note that the shaft has a flat side between the bearings that must be turned toward the crank in order for it to clear the crank counterweights.

The bad news is that the bearing is a proprietary sized double row bearing, and Yamaha wants $90 each for them. I've had no luck cross matching it yet, but I haven't given up yet, either. I did replace only the one that failed, though, and I didn't pay retail.

So, I suggest you check the balancer shaft bearing for clearance as you do any impeller shaft/seal service. You could end up avoiding a repeat failure, or possibly worse.

 

If the bearing(s) need replacement, check here for the details of the in-frame replacement process:

 

http://www.thumpertalk.com/topic/1059507-07-wr450-help/?tru=GKvpN#entry11302329

Very informative. Thank you, and let us know if you ever find that bearing anywhere else.

Wow, that's really good to know, Gray. Thanks!

Great info. You would have never thought.

It also accounts for the iron I've been finding on my mag drain plug and in the oil samples.

Hey Gray I know this is a old thread but is there anyway you could give me the part numbers for the counter balancer bearings? I have to replace both of mine. Thanks.

Because I don't know which bearings are the counter balancer bearings.

Then how will you replace them?

What year's your bike?

I just check it and the 06 and 07 have different part numbers. Will the 07 countershaft bearings fit the 06? The 07's are cheaper.

I just check it and the 06 and 07 have different part numbers. Will the 07 countershaft bearings fit the 06? The 07's are cheaper.

Im not sure, the part numbers are different for the bearings but the same for the shaft. You probably have to get the 2006 bearing but its still cheaper then motosport.

Edited by mxr300ex

Twin County is the cheapest place ive found for Yamaha oem parts.

That's great if he has an '07-'09. What if he doesn't?

That's great if he has an '07-'09. What if he doesn't?

Read after my first post we already discussed that. He has a 2006 and we discussed it has a different part number and he can still find the part he needs on the link I posted just by changing the year of the bike.:thumbsup::thumbsup:

I am hoping they fit. I went ahead and ordered the 07 bearings, the shaft and crankcase is the same on the 07's so I think I'm good.

I am hoping they fit.
Do keep us posted.
Do keep us posted.

Don't worry, I am sure I will have questions.

When I had a leak spring up in a water pump that I had just resealed a couple of rides ago, I decided to investigate.

The impeller shaft has only one single row ball bearing on it. In order to hold a shaft on a single axis, you need a minimum of two. To address this, Yamaha inserts the impeller shaft into a machined pocket in the end of the balancer shaft so that that shaft supports the impeller shaft as well as driving it. The right side balancer shaft bearing then, becomes the second bearing on the impeller shaft, and the shaft is held on axis over its length as it rotates.

But here, I had a new shaft and seal already leaking. Something wasn't right. On inspection, I discovered that the right side balancer shaft bearing had a considerable excess of clearance. Measured with a dial indicator, it was over .015", clearly indicating a failed bearing. Because of the shaft lengths involved, .015" at the drive end of the impeller shaft would be exaggerated to around .020" or more at the seal, and since the balancer shaft is deliberately out of balance, it would necessarily force the drive end of the impeller shaft off axis as it spun, and the seal would have to try to follow that oscillation.

There is good news and bad news. The good news is that the balancer shaft bearings in the '06+ Gen2 engine can be replaced with the crankcases assembled and in the frame simply by removing both crankcase covers, removing the drive gears, counterweights, and bearing retainers, and driving the shaft out one side from the other. This needs to be done skillfully to avoid damage to the shaft, and it is important to note that the shaft has a flat side between the bearings that must be turned toward the crank in order for it to clear the crank counterweights.

The bad news is that the bearing is a proprietary sized double row bearing, and Yamaha wants $90 each for them. I've had no luck cross matching it yet, but I haven't given up yet, either. I did replace only the one that failed, though, and I didn't pay retail.

So, I suggest you check the balancer shaft bearing for clearance as you do any impeller shaft/seal service. You could end up avoiding a repeat failure, or possibly worse.

I've had a strange failure on my water pump on my 07 wr450 I discovered today. I have a trail tech vector and noticed the last couple rides the bike getting too high of temps when cruising high speed low throttle. Pulled my rad cap with the bike idling and couldn't see any coolant movement in the rad. So pulled my water pump cover and found I could freely spin the impeller. So I pulled the right side crankcase cover and found my balancer shaft was full of a brown muck and the inside sleeves were completely corroded out. Somehow some moisture must have gotten trapped in there and rusted it out. Impeller shaft end was fine. My theory is it must have either seeped down the impeller, not likely with the flange end, or come from the oring on the coolant passage just above. This is a high hour bike, 450hrs, have done impeller shaft, bearing and seals once before.

So my question is when removing the balancer shaft how will I be able to tell I am lining up the flat side to the crank? Is it visible?

I'm replacing both bearings as well but I managed to find them for $30 a pop :smirk:

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