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Rattle that changes with RPM -Johnson 90hp

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wallyuwl

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Took boat out for first time this year. 1985 Johnson 90hp v4. Faint rattle or tapping sound that gets faster but not really louder with increasing RPM. Not present at idle. Motor runs fine except for this rattle. It seems like more of a plastic sound vs a metal sound.

Toward end of last year I replaced the stator and then took it out. Ran great. Since then the only thing that has changed is I took my new torque wrench and set it to 102 ft lbs and tightened the flywheel nut a little more. I also changed lower unit oil. Before taking it on the trial outing late last year to test the stator I tightened flywheel to 100 ft lbs with my old torque wrench. Spec is 100 to 105.

I plan to put it on the hose tomorrow. Anything obvious I should check? I do have a nice voltmeter with DVI adapter and factory repair manual if needed.
 
Ok so this is what I did.

First, I took off and put back on the flywheel. I did this first since the only change from last fall when it ran great last time out to this summer is I slightly tightened the flywheel nut in spring. Tightened the nut to 100-101 ft lbs this time.

Looked on my OMC repair manual for compression test instructions......

Ran the engine to operating temp. During this time I did NOT hear the rattling/tapping noise.

Took out all plugs.

With plugs out and full throttle via handle it doesn't start (starter doesn't engage). So I just moved the choke lever to full. Turned key 6 or 7 times. Did this for each cylinder.

Right side (looking at motor from inside boat) were both around 89 or 90. Left upper was 91ish. Lower left 87ish.

Manual does not give specs, only that they should be 15 psi or less difference.

My tester is just a cheap one off Amazon so hope it is fairly accurate but not sure.

Reinstalled the plugs and ran it and all seems fine. Runs good, no rattle.

Should I just take it on the lake and see how it does, or anything else I should check?
 
Compression should be about 120 PSI.----Perhaps test with another gauge.----Throttle does not need to be open when testing that 2 stroke motor.
 
racerone said:
Compression should be about 120 PSI.----Perhaps test with another gauge.----Throttle does not need to be open when testing that 2 stroke motor.
Click to expand...
I think the gauge might be bad. Last year after I got it all compression were 115-120 range (I tested with engine cold and no throttle, but those don'tseem to matter much). It could have gone bad sitting in the garage over winter. But they are still all close and, as of now running on the hose, the noise is gone. I will probably get a different one soon, though.
 
racerone said:
A loose flywheel would certainly make some noise.
Click to expand...
It is weird. I replaced the stator last Sept and tightened flywheel 100 ft lbs with my old harbor freight torque wrench. Took it out a week after the repair and ran great.

I got a new Husky torque wrench over winter because the HF one started slipping last summer. This May I tightened the flywheel nut to 104 ft lbs with the Husky (spec is 100-105) (did not Uninstaller flywheel, just tightened nut). Take it out a month later (yesterday) and I hear the rattling.

Today I take off and reinstall the flywheel, tightened to 101ish with the Husky and it runs great in the driveway on the hose with no rattling.

Odd that tightening the nut would cause a problem. But as of now it seems fine after what I did.
 
Possible that flywheel was not seated properly on the key.-----Note the key positions the flywheel for proper timing.------It is driven by the locking tapers.
 
So I took it out last week and heard the rattle again. This time I even heard it slightly while at idle, but still is much more pronounced when in gear and louder as rpm increases.

So I put it on the hose in the driveway again and it ran fine with and without the cover on. No rattle. I got a different pressure gauge off Amazon and it read all cylinders 90 to 100 psi. Seems to run too good for that to be correct.

Since it doesn't do it on the hose, I wonder if it could be something to do with lower unit (related to back pressure while in water)?

It does die pretty easily while on the hose (buy not in water), but it has always done that.

I did get on the waiting list for the dealer to check it out.

Any thoughts on things i can check in the meantime?
 
I had something similar to what you are describing that was driving me crazy. Turned out to be a cowling latch that had loosened up just enough to rattle. It's worth checking.
 
EODJay said:
Yes. Hopefully that's all it is for you.
Click to expand...

Unfortunately it wasn't it. But I did appreciate the suggestion.

It made the rattling/ticking noise right away in the water. It is more noticeable if you are going kind of slow then accelerate a little (louder during the acceleration phase).

Took the cover (cowling) off in the water and it definitely seems like it is coming from the flywheel or something attached to it. From what I could tell nothing was rubbing against it.

Ran it WOT for 7 or 8 miles. Stopped and did WOT again a few times. Each time once RPM hit about 4400 (maxes out 5000) the noise stopped and it ran like a top!

Got home, put it on the hose with and without the cover and no noise. Put my torque wrench at 100 ft lbs and the flywheel nut was/is tight.

The weird part is it only makes the noise in the water where there is back pressure.

Video (audio) attached.

 
Reading a little more... could it be a flywheel with bad magnets? What am I looking for to determine if magnets are becoming delaminated?
 
I doubt it is an issue with those magnets.-----Those compression values lead me to believe your motor is worn out.----Some here will scoff at my trouble shooting tips.----Remove a couple of transfer port covers and look at pistons and rings.-----Compression on a healthy motor is around 120 PSI.----Yes I know your neighbor will say 100 PSI is fine !
 
racerone said:
I doubt it is an issue with those magnets.-----Those compression values lead me to believe your motor is worn out.----Some here will scoff at my trouble shooting tips.----Remove a couple of transfer port covers and look at pistons and rings.-----Compression on a healthy motor is around 120 PSI.----Yes I know your neighbor will say 100 PSI is fine !
Click to expand...
All compression 115 to 119 (got a new gauge). Gear oil isn't leaking and has about 2 to 3 hours on it since changed.

Next step take off flywheel and look for problems? Are there bearings between flywheel and lower unit?
 
????---Bearing at the top of crankshaft.-----Bearing on center journal of crankshaft.-----Bearing on the bottom of the crankshaft.----Bearing on big end of each rod.
 
racerone said:
????---Bearing at the top of crankshaft.-----Bearing on center journal of crankshaft.-----Bearing on the bottom of the crankshaft.----Bearing on big end of each rod.
Click to expand...

In reading, a bad crankshaft Bearing can cause such a rattle, or delaminated magnets on flywheel (but this flywheel has integrated magnets.

Flywheel has some play right to left, maybe 1mm. At least double that amount forward and back.

I could replace the crankshaft assembly and bearing, but want to be pretty sure what it is before throwing $200 and 2 hours at it.

Video of moving flywheel.

 
racerone said:
If you can replace the crankshaft in 2 hrs , you could make a lot of money.----Get that dream job at a boat shop.
Click to expand...

The assembly and bearing. Not entire crankshaft.

Do you know what type of noise a bad upper crankshaft bearing would make? Groaning? Rattling?

Does the flywheel movement in the prior video seem excessive?

I found this thread, my problem seems similar.

top bearing on crankshaft is going bad

I was told my top bearing on my crankshaft of my v-4 johnson is going bad. Can i use the engine for a couple of days before i get it repaired.Thanks
forums.iboats.com forums.iboats.com
 
Bearing housing #3 contains a roller bearing.-----That bearing rolls on the crankshaft.------If bearing has as much play as shown in your video , then crankshaft will be scrap too.----Live and learn about these fine motors I guess.
 
racerone said:
Bearing housing #3 contains a roller bearing.-----That bearing rolls on the crankshaft.------If bearing has as much play as shown in your video , then crankshaft will be scrap too.----Live and learn about these fine motors I guess.
Click to expand...
Thanks for that info. Would love to upgrade, but have put too much time and $$$ in this motor (including boat itself and trailer) over past 5 years. Just not worth it now. But parts are getting hard to find.

Would there be a knocking if camshaft itself was bad? Everything I have seen is flywheel play is probably the bearing, and if no knocking crankshaft is probably fine. Rattle/tapping just started within last 2 hours of use.

Does it take special tools, or have to open up the whole engine, to replace crankshaft? I have the factory repair manual.
 
racerone said:
Why did you mention a ---camshaft ----For this motor??
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I meant crankshaft.

I am going to install the new top bearing and see how it goes. If that doesn't fix it then I will take it in around October. The place I would take it estimated 6 to 8 hours labor to replace crankshaft. Crankshaft used is about $55 to $100. Then it is just a few normal bearings and seals to replace for parts (I would already have most expensive part). But hopefully me replacing the upper myself fixes the movement and noise.
 
The new upper crankshaft bearing changed the noise a little at mid RPM. It made the flywheel move less, especially in the forward-backward direction. So it probably was good to change it.

I was at a loss as to what to do next so I took it in. The mechanic told me it is very likely a connecting rod bearing going bad. But it is not bad, that only probably 5% of people would even notice the noise. He said to keep using it and I might even get another ten years out of it before it needs to get done.
 
if a bearing is goin bad the proper thing is to change it before it ruins a crank or throws a rod id never let a bad bearing go 10 years but its your call
 
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