'97 20HP Johnson Noise/Vibration Issue

[TurboDan]

Hi Folks,

New to the forums here, but I think I've pretty much stumped everyone at the usual forum I posted at, and it never hurts to find a new board to check in on and meet some new boaters!

I was wondering if anyone had some input on an issue I'm having currently with my 20HP '96 Johnson, attached to a 14' aluminum boat with remote start/center console.

My original post on this on another forum, followed by an update after I put on a new prop today:

I have to say I'm a bit disappointed. I took my boat out yesterday for the first time in two years two days ago, and everything worked PERFECTLY. I was overjoyed. I took it out for a spin this afternoon, and the story was a bit different. A weird problem I was having two years ago came up again.

Basically, the engine runs fine, idles fine, gets up the speed fine, and performs fine in fast idle too. The boat always starts off without any problem, but once it gets up to speed near WOT, there is a vibration felt and a "rummmm" sound that sort of "under" the regular engine sounds, if that makes any sense. To be honest, I can't even pinpoint whether the "rummmm" sound is coming from the engine or not. It is nearly constant at WOT and at speeds right below WOT, but is not present at lower speeds whatsoever. The noise gets louder when the bow of the boat goes higher in the air due to wind or a wave (it's only a little 14 footer). When the boat goes over a wake and slams back down, the noise actually stops for a moment, but then comes back. Mostly, the noise and vibration is present on plane.

I'm not sure what this could be - or why it happened today but not two days ago when I went for a ride. Everything is exactly the same today, except the wind is a bit stronger.

UPDATE

OK, put the spare prop on this afternoon. Looked it over with someone at the marina, and basically both props looked just fine, but I put the new one on and also put brand new washers/bolts and everything too just to be safe.

Take the boat out, and the noise and vibrations appear to be gone - until I turned around to go home. It's strange, but it almost was like as soon as I turned to go into the wind, the grinding noise and vibration started up. Once it starts up, no matter what direction you're going in, you'll hear it from that point on. I made sure there were no lines hanging or anything like that (this noise would be too loud to be that anyway!). The other strange part is that I simply cannot figure out whether the noise is coming from the engine or not. While in the water, I stopped the boat and then let it run in fast idle. As I increased the RPMs, the noise did not sound. It sounds like the noise is coming more from the port side when looking in the direction of the bow. It gets louder as you travel faster, however, and is more frequent at higher speeds.

The other thing is that through all of this, the boat performs just fine. There's nothing abnormal in the way the boat handles and the engine seems quite strong, just as it always has been. This nagging griding, rummmming sound with the vibration is driving me crazy, though.

Any other ideas would be helpful, since the spare prop I have didn't do the trick.

So there you have it. I'm stumped, and I shudder to think about even having a mechanic LOOK at this thing at $125/hour! It'd wind up costing more than my boat cost a few years back!

Any help would be VERY much appreciated!

Thanks!

 

[rickdb1boat]

Re: '97 20HP Johnson Noise/Vibration Issue

Hi Dan

I'm betting that it has something to do with the aluminum hull. Especially since it changes when you head into the wind. Waves and turbulant water can make funny sounds on an aluminum hull. I think your motor is fine. Of course, the best test would be to drop your motor on a different boat and see if it does it, but that might be a bit extreme...Even my pontoon boat makes a different noise when heading into the wind or in certain choppy conditions...Kinda of like a growling sound from the water slapping the hull..

 

[xtraham]

Re: '97 20HP Johnson Noise/Vibration Issue

something may have sliped through a crack check for anything laying in the boat loose rub rail ect.

 

[TurboDan]

Re: '97 20HP Johnson Noise/Vibration Issue

Rick,

I was thinking that too, but I don't know what it could possibly be about the hull. It didn't always make that noise. I hope something isn't permanently damaged in the hull of the boat! That would definitely be a worst case scenario, I think.

It definitely sounds alot louder than water rushing - more like a grinding noise with a "rummmmm" overtone to it. I'm not sure if vibration from something is causing a noise or the noise is causing the vibration. Also, the other strange thing is that once it starts, it won't stop even if you change into the direction where it didn't happen five minutes before.

If I at least knew it was a mechanical issue with the engine, I'd take it to a mechanic, but I'm not sure if it is or not. It's coming from the area where the engine is, but it's almost "surrounding" the engine rather than coming from it. I'd hate to take it out of the water, bring it to a mechanic, only for him to start replacing things that "might" be causing the issue when none of those parts even needed replacing. Again, you don't hear the noise or feel the vibration at fast idle.

Perhaps a mechanic at my marina would go for a quick ride with me one day? Not sure if they do that with potential customers or not, as luckily I haven't needed their services in the past.

 

[rickdb1boat]

Re: '97 20HP Johnson Noise/Vibration Issue

What is odd to me and I'm sure to you, is the fact that it does not do this all the time. Adding to that is that water or wind conditions can make it come or go. You may want to have someone ride along and either drive or sit by the motor and see if the noise can be isolated. Maybe a hand placed on the engine to feel for different vibrations and such would help. I've never had that problem in my little fiberglass runabout, but do notice different sounds on the toon. I've pretty much learned to live with them and consider them normal. But I realize your concern that there may be an engine issue. Only you can decide if it's worth spending some money to ease your fears. The ride-a-long mechanic deal would be the first choice, even if you have to slip them a few bucks for their time...

 

[TurboDan]

Re: '97 20HP Johnson Noise/Vibration Issue

Yup, that's basically my thinking exactly. If I knew it was just a noise that has come to be, I wouldn't really care too much. I'd learn to live with it and probably would eventually get used to it coming every now and then.

Hehe, and the obsessed boater in me broke through tonight - I HAD to go out and take another ride after dinner! Just got back about five minutes ago. Good thing no one came with me to try to isolate the noise tonight - because there was no noise! I actually was TRYING to get the noise to come so I could hear it and it wouldn't. I rode into the wind, out of the wind, made sharp turns, brought it down to idle and then revved it up and got on plane, jumped another boat's wake - zero noise at all. The wind wasn't as strong as today and the bay wasn't nearly as choppy as this afternoon - but still, I found it very odd.

The only thing I did differently was put some of my gear at the bow to add some weight there. I guess I'll keep trying different things until I can find out what's going on. My Dad's going to come out with me tomorrow night and see if we can hear anything then. Maybe two sets of ears (and two bodies in different positions in the boat!) will allow us to see something new.

I'll keep the board updated!