25 HP Yamaha 2 Stroke noise when running slow.

[jimmer]

I have noticed that my small outboard has started to make a noise (not overly loud, but I know it's there) when running at slow speeds. I'm thinking that there is a bearing for the drive shaft that might be making the noise. Any others suggestions from anyone would be appreciated.
The motor runs great and trolls no problem, never stalls, so I'm sure it's in the drive. I don't have much experience with the what's under the fly wheel (?), is it possible it's something up top rather than under the engine?
I wish they would put grease fittings all over the motor. LOL
Thanks,
Jimmer

[Marker]

I would get a long metal rod or section of hockey stick, with the motor running place one end behind your ear and the other end touch different parts of the motor and drive area, you will notice the noise getting louder where the problem is.

I would also change the lower end oil, keep a small sample of the old oil and you can take it to a shop who can determine if you have metal in it. But if you do have a bearing gone in the lower unit the old oil will be black with silver bits, and larger bits may come out with the oil.

One final comment: make sure to run the correct ratio of two stroke oil in your gas as a pre-mix, do not trust those vacuum operated oil pumps to supply the 2 stroke oil, I have seen a few connecting rod bearing failures due to those little oil pumps that gum up.

[Fenelon]

First thing I'd check is the water pump. I've run a fleet of Yamaha 2 strokes and that is the one weak item that consistently goes. The older models had crappy impeller material. Early premature wear, esp. if you do a lot of shallow water work, or you leave your motor in neutral while trailering (spinning prop dry rubs your impeller in the housing). Check your pisser strength. If it's low, I'd overhaul the water pump. I'd also check the compression next.

[Wahoo]

Having just replaced the crankshaft bearings, piston and rings in a 5HP 2 stroke single cylinder Merc this past winter, pay careful attention to how your motor continues to perform. My motor, unlike yours, was running like crap and it would vibrate bad. The only way you can find out what MAY be wrong if you believe the problem lies somewhere in the engine area, is to pull the powerhead and check for noises. That's how I finally found my problem - I spun the crank and heard/felt the bearings on one side. After finally cracking the cylinder, the one bearing was completely disintegrated and the associate seal ruined. I couldn't believe that the motor would even run like this!

Continue paying attention, if things change noticeably it may be time to start disassembly.

Here is a link to some parts schematics: (you can pick appropriate year, I guessed)

http://www.boats.net/parts/search/Ya...SHC/parts.html

Start thinking about getting a Service Manual.

[jimmer]

Thanks guys.
I do change the lower unit oil every year and it looked good.
No problem with the water pump, good strong stream.
I do pre-mix my gas/oil and it is a 100:1 ratio mix.
Compression is good.
I'm fairly sure the noise is in the drive above the water line. Must be a bearing/seal on the upper part of the drive shaft.
I will try the ear and tube idea for sure to pinpoint the noise.