Water in Yamaha 25 Lower Unit Question for outboard mechanics : (

Bill Burruss

Bill Burruss

Well-known member
All,
Decided to do a little pre-season maintenance on the 2004 Yamaha 25 HP 2-stroke that powers my BB2, and when I drained the lower unit oil had a good bit of water come out. Have never noticed so much as an oil stain around the prop shaft area. Does this indicate that the leak is from the input shaft (seals are under the impeller), or could the problem be the prop shaft seal, and it just stays clean because the engine runs in water? I'd already ordered an impeller, so I figure I'd replace the input shaft seals while the lower unit is off. The engine has about 140 hrs, and this is the second or third oil change and the first time the lower end has come off (been meaning to change the impeller for some time). Also, the the boat is garage kept, but most outings are in salt water. Anything else to watch out for or thougts on the problem?


Thanks,
Bill
 
Bill ,

It sure sounds like you have a bad shaft seal , the only thing to do is to replace it but while you are doing that , change out the water pump and flush the gear housing out good with oil or another type of lubricant , i run my Honda in salt 90% of the time and rinse it everytime we return from an outing , in installed a self flushing valve outside so i can even rinse it out in the cold New England winter days , My guess is a piece opf fisihng line maybe got wrapped around you prop shaft and cut the seal , but that is just a guess , i have had that happen on another outboard i had , Good Luck it is not a bad fix but definaely need attention before you cause any more damge to the gear box . have a safe seaon !!



Dave M
 
Also be sure to replace the oring or gasket for the filler\drain screw. If the boat sits in the water that can be a source.
 
All,
Thanks- the comments here really helped. Richard got me thinking when he said pressure test, so I did a little more research on that subject. With this set up and 15 lbs of pessue, a bubble burps out of the water intake every minute or so, which I think confirms the problem is the input shaft seals (upper seals), and not the prop shaft.

The adpater in the oil hole is actually from a lower unit fill pump I bought for changing lower unit oil in my Yamahas (probably not needed for what I am doing here). The threads screwed into the lower unit are metric, but the threads the air hose is against is SAE. I plan on getting some more hardware so I can presurize the case and see if it holds pressure with the new seals. From what I've found on-line, 10-15lbs initial should have some residual pressure after an hour.

Thanks again !

-Bil

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