Tohatsu outboard whine ??

[krissteyn]

Both my 8hp 4 stroke and my 9.8 2 stroke have a transmission whine when above idling speed that becomes inaudible at higher revs...
My local outboard mechanic says it a common problem...
I bought both engines almost brand new from being bought new but boat changed owners and new owner wanted bigger n faster.
The 9.8hp developed the whine after I purchased , and the 8hp got louder after I bought it...
I use the motors at around 75% throttle to get my 3.1m RIB to plane...
Anybody have a cure for the whine ???
I've changed the bottom oil in both cases soon after purchase with reccomended gear oil...

[pbiJim]

My 3.5hp, 5hp, and 9.8hp Tohatsu 4-stroke motors did not whine.

[krissteyn]

Yes , it's not everybody's that does - that's why I want to cure it ��

[GordMay]

Electric start?

[krissteyn]

Not electric start , but good question...

[abroadreachtrvl]

Pour the oil though a coffee filter, is there any debris? Same noise in neutral?

[krissteyn]

Havnt strained the oil , but the noise appears to not come from the lower end...
Bear in mind this is a fault that is not unique - it's a well-known complaint.
Neutral is without the whine....
I'm trying to get a contact for the head office R and D , but so far havnt got a "real" contact...

[Tedd]

I had an 8 HP Tohatsu on my old boat that had what I would describe as a whistling sound at cruise power. Perhaps it's the same thing?


I always believed that the sound from my engine was from the induction system. It did not change when I replaced the carburetor (for unrelated reasons). My leading hypothesis was that it was from the reed valves, although I'm not even certain the Tohatsu was a reed-valve design. You could try running it in neutral to isolate the drivetrain. That's not a definitive test, though, because an induction sound would be load-dependent, not just RPM-dependent.



Incidentally, I once did a survey about how field technicians describe mechanical sounds. It turns out that the range of interpretation of any adjective--whine, whistle, squeal, squeak, grind, crunch, bang, boom, click, and so on--is so wide that the words on their own are essentially useless.

[pbiJim]

Originally Posted by Tedd

...My leading hypothesis was that it was from the reed valves, although I'm not even certain the Tohatsu was a reed-valve design....

As far as I know, the 2-strokes have reeds & the 4-strokes do not.

[Mirage35]

I had a Tohatsu and whined about it a lot. Changed for an electric and that annoying noise stopped.

Sorry, I just couldn't resist.

[motion30]

My 20 hp merc has a whine
I think one factor is they are much quieter than the previous 2 strokes. I can hear the four stroke shift much louder as well

[pbiJim]

This is not outboard specific, but rather a general statement regarding motors that I have assembled.

What I call a whine, is normally caused by gear clearances being too tight. When they are too loose, I often get a clacking sound. In some motors, it is possible to purchase gear sets with different pitch diameters to compensate for clearance issues. In other motors, shimming, or sleeving is the fix. A difference of 0.0002" (two ten-thousandths of an inch) is enough to make the difference. A piece of paper is generally around .004" thick. That is 20 times as much. This issue is something to look for when a newly assembled motor whines immediately.

When a whine develops over time, it is something different. Something has moved. Something is likely rubbing or biding. This can be due to overheating. It can be due to something having been bent after being hit. It can be from wear. Often wear problems result from lubrication problems.

This is Tohatsu outboard specific - Check to see if the little red light works when you turn the motor over. If the light does not work, then you will not know when the engine is running in a damaging condition.

[krissteyn]

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[krissteyn]

Thanks Jim , yes the little red light comes on normally...
Without more info from this knowledgeable group , I'm not going to strip the motor. I don't have a workshop and doing it as a liveaboard is not simple...

[krissteyn]

Thanks for reply Ted , the noise is more of a whine than anything else IMO
It's apparent on my 2 stroke 9.8 and the 4 stroke 8hp...