The YZ400/YZ426 Transmission Blues

Hey fellow YZ400/Yz426 riders: The 400's and 426's are great bikes but last fall my countershaft bearing went out and broke the cases and a bunch of other internal parts. It cost me about $800 to fix it. I think the seal behind the countershaft sprocket went bad and dirt wore out the bearing. Keep an eye on the seal to make sure it doesn't leak and check the bearing for play.

What is the recommended chain adjustment knowing the history of the broken hubs?

Originally posted by Berm Buster:

I think the seal behind the countershaft sprocket went bad and dirt wore out the bearing.

Your chain may have been too tight, a few guys here noticed that the tension spec. in the manual was a bit on the tight side and suspected too much chain tension was causing hubs to break. The same effect could ruin a countershaft bearing.

Do a search for “hub failure,” there are several threads on the chain tension subject.

Or it could have been some trail debris wedging under your chain that did it. Were you riding in mud when this happened?

I had a rock wedge between my contershaft sprocket and chain.. Bound everthing up bad enough that it locked the bike up as I was doubling and tripling thru some whoops. Major get-off and major damage. Something like this may have happened to you causing the problem.



Thanks for the replies. When it happened it was a dry dusty practice day. It could have been a rock but I didn't hear anything. The bearing was in so many pieces, even the steel race was gone. I have always used a o-ring chain which has some additional resistance but I think it was always loose enough. I would check it by compressing the suspension and make sure it had plenty of play. I bought it used and had problems keeping the sprocket bolts tight at first. The sprocket holes were egg shaped and once I bought a new sprocket, the problem went away. Maybe the original owner had it too tight and put too much stress on the bearing. Thanks for the advise, I almost have it back together and will be riding soon.

Those egg-shaped holes may have also been caused my too much chain tension. Sorry for your bad luck.

You may consider checking the applicable tension for your gearing the next time you service the linkage by checking the tension at the tightest point in the swingarm’s travel.

Meanwhile, a bit too loose is better than a bit too tight.

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