I think 'seat' is a typo. I think he meant 'seal'. The flexible valve stem 'seal' lets oil pass down the valve stem to the valve stem/valve guide interface.
If the seal is too tight on the valve stem, little or no oil will make its way down to the stem/guide interface. If it's too loose on the stem too much oil will be lost down the stem and you'll see oil consumption.
The stem/guide interface needs a small amount of lubricating oil. The stem seal is supposed to provide a 'metered' leak that passes just enough oil to keep the stem/guide wear to a minimum for long operating life.
This line of inquiry by Yamaha may have merit. Yet, it would seem that the seals would have been one of the first areas of interest in resolving this problem.
If the seal is too tight on the valve stem, little or no oil will make its way down to the stem/guide interface. If it's too loose on the stem too much oil will be lost down the stem and you'll see oil consumption.
The stem/guide interface needs a small amount of lubricating oil. The stem seal is supposed to provide a 'metered' leak that passes just enough oil to keep the stem/guide wear to a minimum for long operating life.
This line of inquiry by Yamaha may have merit. Yet, it would seem that the seals would have been one of the first areas of interest in resolving this problem.
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