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These are the gearcases on the triples . There are 4 different sizes 25 & 30, 40 & 50, 50 & 55, 60 to 90 hp. I first started running Yamaha motors in 1984 when I purchased a new 30 hp triple (non oil injection) . I have owned all the other gearcases mentioned and I having a lot of history with them.
First off the most common reason most gearcases fail is lack of proper maintenance! People don’t check the gear lube in the gearcase often enough. Water gets into the case, it ruins the gears or it freeze over the winter and cracks the case. Next reason is hitting something. Serious damage is noticed immediately, but many times minor prop damage goes unnoticed and it gradually creates a gearcase problem.
Poor shift cable & throttle adjustment and engine maintenance will hurt the gearcase over time. The motor idle is too high, the cables aren’t adjusted correctly or the motor hasn’t had a needed tuneup.
Lastly some people just abuse their equipment!
So with proper care how long with these gearcases last? Remember a new gearcase are now very expensive. More than doubled in price. But there are used ones on the market that can extend the life of your current motor.
So here are my findings with the 4 Yamaha gearcases:
If you don’t know the history of the gearcase. Inspection is a must. If it doesn’t look or feel right(when you turn the drive shaft and shift gears) Be cautious. Always have a prop on it when you turn the prop shaft to see if it is straight! Even a trained person can miss a bent prop shaft looking at it without a prop on.
Check the gear lube. If there is water in it it will come out first when you loosen the lower screw. Milky gear lube is water in the lube. Blackish color shows lube hasn’t been changed . If it shifts, the gearcase is likely good. You may not notice a shift dog issue with a 60 to 90 hp gearcase. You will notice it when you run it on boat water test.
Always best to dissemble and replace seals and O rings on any used gearcase.
The 25 & 30 hp triple.
Other than bent prop shaft. I have never seen gear issue. Most times the gearcase shows very little wear.
The 40-50 hp (6H4 & 6H5)
No issues
The 50-55 hp (70CES)
There are two cases
Bolt in carrier
Regular style
Two issues:
Both are turn to shift styles. There can be gear problems. Shift dog is more common.
On the bolt in carrier type the bolts loosen and the carrier loosens.
The 60 to 90 hp (6H1)
Turn to shift gearcase....there can be shift dog and gear problem.
These are my findings.
What have you found?
Any suggestions....gear lube type etc....assembly tricks?.....better replacement parts?....where to find parts?
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