Strange sounds coming from a 3 cyl 2 Stroke 90

[ct0218]

Yesterday, after a 20 minute run at 4200 rpm back to the ramp, I noticed my Merc 90 making an unusual noise. Sounded like a belt or pulley squeal, not extremely loud or continuous, but noticeable. I never run the motor hard, and it did the same thing coming back to the ramp about 2months ago. A dozen or so trips in between, it did not happen. I shut it down at the dock, backed my truck and trailer down, less than and when I cranked it back up it sounded normal. My first thought was that the impeller was about shot, but when I pulled the lower unit today it looks like a new one. Stumped as to what that sound could be. The motor has always run perfectly---except for this sound twice now. Any thoughts...?

 

[schematic]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

serial number?

 

[Texasmark]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

3 cyl 2 stroke 90: No belts or pulleys. Only thing I can think of is a dry bearing that gets dry periodically. I assume you are using TC-W3 Marine oil in your injection system and that it works. Easiest way to tell is that your oil level in the tank drops. If in doubt you might add a pint of premix to 6 to 12 gallons for a tank and see if it repeats or not.

If not you might choose to disable your injection oiler. I did on my 90 and it is quite easy......just don't forget to add that oil to the tank. If you use Pennzoil premium plus it states on the container it is semi-synthetic and smokes very little ion my engine. It's my oil of choice and run it exclusively. Almost can't tell it's a 2 stroke, even in the hole shot. Merc won't disclose what's in their premium plus so I run Penn. Besides it's about half the price at WW. So I wouldn't worry a bit about excessive smoking gumming things up. You aren't going to be running it that way all that long anyway. If you are worried about it, put Sea Foam in your gas and it will clean your engine of any deposits the extra oil may cause. Putting SF in your gas anyway is a great idea. I redid my carbs recently on a 10 year old engine and there was absolutely ZERO fuel deposits in the bowls.

Mark

 

[ct0218]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

3 cyl 2 stroke 90: No belts or pulleys. Only thing I can think of is a dry bearing that gets dry periodically. I assume you are using TC-W3 Marine oil in your injection system and that it works. Easiest way to tell is that your oil level in the tank drops. If in doubt you might add a pint of premix to 6 to 12 gallons for a tank and see if it repeats or not.

If not you might choose to disable your injection oiler. I did on my 90 and it is quite easy......just don't forget to add that oil to the tank. If you use Pennzoil premium plus it states on the container it is semi-synthetic and smokes very little ion my engine. It's my oil of choice and run it exclusively. Almost can't tell it's a 2 stroke, even in the hole shot. Merc won't disclose what's in their premium plus so I run Penn. Besides it's about half the price at WW. So I wouldn't worry a bit about excessive smoking gumming things up. You aren't going to be running it that way all that long anyway. If you are worried about it, put Sea Foam in your gas and it will clean your engine of any deposits the extra oil may cause. Putting SF in your gas anyway is a great idea. I redid my carbs recently on a 10 year old engine and there was absolutely ZERO fuel deposits in the bowls.

Mark

The motor is a 2002 ELPT, sn 0T510493. I regularly use Seafoam and Stabil Marine Formula. I have used Amsoil full synthetic TC-W3 for the two years I've had this motor, and prior to that for 10 years in my Yamaha. The oil reservoir is full, and it never gets below half full. I've never had any issues with the oil. Just strange that it has happened twice now, with the long break in between. I idled for 5 minutes at the dock, and the sound never changed back to normal before I shut it down. Less than 5 minutes later it sounds normal again. Weird. The carbs look very clean

 

[schematic]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

Get a stethoscope (cheap) and probe around the engine while its making the noise. Pay close attention to the oil pump.

Of-course the leg oil is OK......right?

 

[ct0218]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

Get a stethoscope (cheap) and probe around the engine while its making the noise. Pay close attention to the oil pump.

Of-course the leg oil is OK......right?

Yep, changed the lube a week or so ago. WHat I drained out looked good after a year. I haven't had the shroud off while it makes the noise, but definitely a possibility since I have no idea where its coming from.

 

[Texasmark]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

Your s/n is within 5000 of mine, same year and OT prefix. I have done a lot of thinking about this and have no answer. If it is a dry bearing, which is all I can think it could be, it's odd that it happens so infrequently.

I have a few thoughts.

I am a firm believer in and user of full synthetic lubrication products. However, Amsoil is the only one of which I am aware that is full in 2 stroke marine oil; but that's their business so one would think that they have to stay the course. I use Pennzoil Super Premium synthetic blend. I pick up on bits of info here and there and possibly there is a reason besides price that Pennzoil stops at the blend rather than going full bore like in other lubes they manufacture. As stated, Merc won't tell you about theirs.

I have operated a fair amount of old farm machinery over the years, still do, and it's amazing how you can take a worn/rusted bearing, throw some lube on it and quiet it down. I can understand that a hiccup in your oiling system could deprive some bearings of proper lube, cause them to squeal at you and recover as soon as proper lube was restored. It could cause an oil burn on the bearing that could contribute to the squeal when conditions are right.

The oil mix in your engine is 80:1 at idle. At WOT it's 50. Idling for 5 minutes is running the minimum amount of oil. Yes engines need more lube at higher rpms but.......100:1 that OMC tried a few years ago got numerous negative comments on here from old salts that knew their business and the main one was corrosion while sitting up.

If you ran some premix to go along with your oiler it would give you a data point. Maybe not 50:1 but maybe 100:1. And if you used a partial paraffin based oil like the Penn I mentioned, that would take care of two unanswered questions that I have. I really doubt you will notice any difference in engine smoke as when I disconnected my oiler and went with 50:1 pre mix using Penn oil, I couldn't tell the difference at idle. And the SF should take care of keeping the engine clean.

You may have a bubble in the oil line from the tank to the pump where the oil line makes a vertical turn.

The upper bearing in your lower unit, the one just below the water pump may not be getting lubed properly. At idle it is spinning at the lowest speed and if the bearing were being deprived you would surely notice it then. I assume you are using the Quicksilver Premium LU lube in the quart bottle with the hose and pump.

That's about it for now. I'll keep thinking about it. Good Luck.

Mark

 

[ct0218]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

Thanks Mark for your input. I will try running some additional oil, but it may be winter before it does it again, who knows. I should add that the noise was obvious as I slowed from cruising to idle. I could hear it as soon as the rpm's started dropping (along with less wind and motor noise). It did continue at idle, but started at 4200 rpm's. At the restart not a hint of an unusual sound.

 

[Texasmark]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

That may be a clue. The F gear setup is an overrun clutch. When decelerating you don't want the prop to stop the boat so the clutch dog sitting on the prop shaft ratchets....aka free wheels. This and the engine rpms dropping take the load off the drive shaft bearings. If I were to expect one it would be the upper one just below the water pump and upper seals, as I mentioned initially. That is a distinct possibility and messing with the engine lube oil won't help.....but you will have an idea as to where to look if it continues after you take the action mentioned on the addition of some pre-mix.

However, idling still puzzles me. Not much stress idling. On the drive shaft upper bearing replacement, it is not an easy job. You have to drop the lower unit and pull out the prop shaft and R gear and carrier. Then reach up in the housing and remove the nut holding the shaft in place, and remove the water pump and all. But you will have the opportunity to inspect all the bearings in the drive line and ensure to yourself their condition.

HTH,
Mark

 

[ct0218]

Re: Strange sounds coming from a 3 cyl 2 Stroke 90

If it ever stops raining I hope to get out Thursday or Friday. I'll try and duplicate the run distance and rpm's. I have a stethoscope on order, couldn't find an inexpensive one here in the mountains, but I doubt it will arrive before I hit the lake again.. If and/or when it acts up again I'll pull the shroud quickly and see if I can at least find the general area the sound is coming from. Off hand it sounded like it was coming from the upper half of the motor, but at that point I wasn't really trying to locate it. I'll let my wife run the boat and I'll spend more time checking it out. I'm holding off on adding oil to the gas tank until I make a few more trips to see if will happen again.