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Bloke wrote:Why not just buy another piston assembly from your closest Yamaha dealer? Their manufacturing control is just about good enough to drop a replacement piston into an instrument with little or no fitting required.

Yep, I did this with my fourth valve on my YEP-641 euph three years ago. It fit just fine - no lapping necessary. Cost as I recall was around $80.

That must be frustrating. If the other valves are working alright, don't spend the euros yet to get it all done at once. Start with just the valve to get your horn playable, and see how the rest are by comparison afterwards. Good luck!

The type or brand of oil is your particular choice, regardless of what the valve is made of. The viscosity depends on the horn. If you get it, and it's a really tight fit, thin oil, and oil frequently. If it has clearances like most horns, just about any valve oil will do.

Yep... the 321 and 201 pistons are interchangable (at least one through three are). I wouldn't bet on the others being the same. Now... serial numbers before 100,000 will not interchangable with later horns, unless you want to also change the valve guide and stem as well as the piston.

Belltrouble wrote:Does this tell that the later pistons use nylon(plastic) valve guides?

Yamaha tubas with serial numbers UNDER 100,000 (such as yours) have the small metal guide that is held into a pocket on top of the piston with a screw. Serial numbers over 100,000 have the plastic guide that is held on by the stem and a washer. No... the plastic guides will not fit the old pistons. You might think they will work, but the hole you might be trying to use for alignment is actually a vent hole and will cause bad radial piston alignment. You can change the entire piston if you want... along with the correct stem and washer.

Don't ask if serial number 100,000 is the old or new style! I wouldn't know. Also, there are no published Yamaha serial number list to date a horn. Yamaha claims there were no recods kep.