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Why does my bike Leak Oil Around the Counter-shaft?

For twenty plus years, these manufacturers have used a “spring washer” or “dome washer” along with a locking bolt to retain 4-stroke and newer 2-stroke counter-shaft sprocket. A retaining ring is used on most 2-strokes. After a year or two of riding, many of these bikes develop an oil leak around the counter-shaft. This often shows itself as streaks of oil lines on the face of the counter-shaft sprocket. When removing the counter-shaft sprocket, most riders immediately see the lip seal pressed into the case around the splined counter-shaft. This is usually what gets replaced in order to eliminate the oil leak. Often the leak still remains after replacing the seal. So how is the oil escaping? We at Dirt Tricks were frustrated as were many, so we disassembled everything possible behind the counter-shaft sprocket. Then we 3D-modeled what we found in order to figure out where the oil was coming from. In the diagram, you will see an “O-ring” mounted in the spacer bushing. That O-ring keeps oil from leaking down the shaft between the counter-shaft and the spacer bushing. The lip seal rides against the outside of the spacer-bushing. What we also discovered, is that every time we noticed an oil leak, the “spring washer” on the outside of the sprocket was not holding the sprocket tight. Then we examined the stock spring washer and discovered that over time, it completely flattened. Often, you can actually spin the spring washer on the bike with the sprocket bolted down. If you study the diagram below, when the spring washer does not hold pressure against the sprocket, the entire stack of parts – from sprocket bolt to the bearing race, is loose. That allows that small O-ring to separate from the face of the bearing race and there is the oil path. Without a functioning O-ring, the spacer bushing is just a pipe for the oil to run through.

The Solution:

When performing hardness tests on the spring washer, we determined that it was not much of a spring, and yielded the first time is was compressed and would not spring back. We solved the problem by producing a through-hardened, tool-steel replacement spring washer that acts like a true spring. When removed, unlike the OEM washer, it returns to its original dome shape. The Dirt Tricks dome washer can be repeatedly re-used. It is extremely hard and tough.
We hope this has not been to over-technical, but with a little detective work, we have solved a simple but nagging problem. So if you have a counter-shaft oil leak, start by replacing your spring washer with the Dirt Tricks dome washer.

~Greg Burns, Dirt Tricks President, Mechanical Engineer. 2016

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