2008 Mercury 20 ELH Whining at High RPM

Hello everyone! First off I would like to say this is a fantastic forum. It's given me a lot of great ideas for fixing up my Grizzly 1548.

I would appreciate some advice on my 2008 Mercury 20 ELH. It's developed an odd whine at higher RPMs and I am having difficulties finding the cause. It begins around 2/3 throttle after you take off and the motor gains momentum. It increases in pitch as you increase RPM and gets quieter. As you reduce throttle it gets louder and then disappears around 2/3 throttle. It almost sounds like a high pitched vibration or "harmonic ringing."

-My first thought was prop sing, but I put an old prop on there and it didn't fix the problem. New prop is an Solas Amita 3, old prop is the stock Mercury with a slightly chewed up edge.

-It only does it in gear, so I wouldn't think it's in the top end.

-I changed the engine oil and found no metal shavings.

-I changed the lower unit oil and found no metal shavings, the lower unit is also shifting fine.

-I removed the lower unit and verified everything looked good with the impeller I put in it last fall.

-I can't find anything loose that would be vibrating. I've also tried running it with the cowl off to find something vibrating.

Short of taking apart the lower unit, I'm not sure where to go from here. Could something be bent? It has been run over gravel bars a couple times, but never hard.

Have you pinpointed the general area of the sound by running it on muffs in the driveway? Could be your timing belt, easy check it to rev it up until you get the sound then shoot the belt with some belt conditioner (or water or whatever) and see if that changes the noise.

Might be worth investing in a mechanic's stethoscope to pinpoint the source of the whine. Cheap tool but I've used one for noises in both cars and outboards. Just watch for moving parts when you're probing around!

I've been wondering about the timing belt. I can check it tonight. It only makes the noise when in gear though. Just revving it up in neutral I get nothing. I've never run a motor in gear while on the muffs. I have run the motor down the lake without the cowl on while pressing on different areas and was unable to affect the noise.

I bought a brand new Tohatsu in 2008, 20hp (exactly the same as a Merc 20), and it was noisy as heck as well. It is gearcase noise. Doesn't hurt anything but my ears. I actually removed the foot and ran it in the water without the foot briefly and it was quiet as a church mouse. Fluid was clean, no metal. Took it back to dealer and he said that they all do it. So I ran it until I got tired of it, sold the boat and motor to my friend who wanted it worse than I did and he loves it--but it's not gotten any quieter.

My 09 merc. 20hp had a whine to it since new. Then one day it decided for no reason at all to eat the pinion gears out of the gear case...... once I replaced the gears and bearings the whine went away.

turbotodd said:

I bought a brand new Tohatsu in 2008, 20hp (exactly the same as a Merc 20), and it was noisy as heck as well. It is gearcase noise . . .

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Yeah I've pretty much narrowed it down to the gearcase. I'm glad to hear I'm not the only one to experience this issue. It just started making the noise this winter.

lovedr79 said:

My 09 merc. 20hp had a whine to it since new. Then one day it decided for no reason at all to eat the pinion gears out of the gear case...... once I replaced the gears and bearings the whine went away.

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I've been running it a couple days and then changing the lower unit oil to check for metal. I think what I need to do is run it longer and see what comes out. Did yours just start wearing suddenly?

mine never had metal in the oil. it ran fine, had that whine since brand new. then one day about full throttle she let go. no warning, nothing.

Usually when you have a whine like that it is a sign that the gears are set up too loose.

lovedr79 said:

mine never had metal in the oil. it ran fine, had that whine since brand new. then one day about full throttle she let go. no warning, nothing.

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nccatfisher said:

Usually when you have a whine like that it is a sign that the gears are set up too loose.

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Is this something that can be adjusted or would I have to replace gears? If I opened it up would I see wear on the pinon gear or any other indicators?

RedL said:

lovedr79 said:

mine never had metal in the oil. it ran fine, had that whine since brand new. then one day about full throttle she let go. no warning, nothing.

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nccatfisher said:

Usually when you have a whine like that it is a sign that the gears are set up too loose.

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Is this something that can be adjusted or would I have to replace gears? If I opened it up would I see wear on the pinon gear or any other indicators?

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I haven't been in one of these honestly. Some others have shims that you use and you check the end play on the shaft and either shim behind the gears or the bearings to get proper clearances.

If you have a factory service manual it would give detailed instructions on the assembly of what you are asking about and you could get your information. Personally I would go that route. I would get a manual and see exactly how it was assembled. If it does show that it does uses shimming to get clearances on those gears then yes, I would most certainly tear into it prior to waiting for it to disintegrate. You most likely would have many parts that would be salvageable instead of waiting for it to fail.

From what I remember there were shims in there. After new years and bearings I want to say they felt tighter. Whine went away

Ok, I've ordered a service manual. I'm going to open it up and take a peek. Thanks for the help guys. I'll report back what I find.

RedL said:

Ok, I've ordered a service manual. I'm going to open it up and take a peek. Thanks for the help guys. I'll report back what I find.

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Good luck with it, I think in the end you will be glad you did.