Shaft problem

[91 Sunsport]

Bought a 91 Supra Sunsport which had been out of the water for approx 1 year. It was in good nick and mechanic said it was in good shape. Took it for a spin and it went great. On the second day we noticed a noise which sounded like it was coming from the shaft as it left the strut (I think) - this noise only happens at low revs (travelling 5 knts or less). I\'m new to this game. What do you think the problem could be and how much do you think it may cost?

Cheers

[DKJBama92Mariah]

Hello and welcome to the community,

It could be the strut bushing, but its hard to tell without knowing more.

What is the nature of the noise? a pop, click, tap, moan, groan, etc.

Does it change in frequency or intensity with changes in engine speeds?

Give us a little more info and i'm sure someone can step up and give you some good advice.

Cheers,
DKJ

[91 Sunsport]

It makes a groaning noise at low rpm. It does change in tone at different speeds but it is completely gone when more throttle is used.

[SupraNut]

Is there any vibration associated with the noise?

[91 Sunsport]

There could be a little vibration but minimal

[91 Sunsport]

Thanks for looking into this for me.

I had it out again this morning. There was no groaning first thing, (I thought it could have been just an aberation - not my luck) but when we were out for say 10 min then slowed it down to 5 knts it moaned at the lower RPM and as the rotation began to slow down you could hear the moaning slow down with it until the shaft stops in the idle position and then there is no noise. I'm guessing that as everything heats up and expands the shaft/something begins to rub. I'm thinking that as the boat has been out of the water for approx 1 year a rubber ring or bearing might be to blame.

[DKJBama92Mariah]

Well, there are three things that i can think of that could be causing the noise: (1) strut bearing, not so bad; (2) shaft packing, still not so bad; (3) transmission, now thats bad.

I dont think its either the strut or the transmission because i would think that they would make the noise all the time, not just after you've been running a while.

Check the strut bushing first because it is easy. It is inside the hole in the strut with the shaft going through it, and it is made of rubber on the inside part that touches the shaft. You'll be able to tell if it is worn out, but i dont think this is the prob because a worn out bushing typically has a vibration associated with it.

My gut is telling me that the nut on the stuffing box is too tight. The stuffing box is what allows the turning shaft to go through the bottom of the boat without letting water in. Here's how it works. The nut on the stuffing box has a flax rope inside it that encapsulates the shaft. This rope is pushed against the shaft by the pressure of the nut tightening down and squeezing it. Here's the catch; A little bit of water (5-10 drips per minute) has to be allowed to pass through to lubricate the flax rope. If the nut is too tight this cant happen and the friction between the rope and shaft will make the whole assembly get HOT.

I would take the boat on a test run with the floor panel behind the motor box removed. With the floor removed, you'll be able to pinpoint the noise to the stuffing box. If that turns out to the the source of the noise, i WOULD NOT attempt to adjust it now. If it has been running too tight, then the flax rope is probably cooked and you won't be able to get it to seal properly without really cranking down on the nut, which is what is causing your problem in the first place (at least if i'm correct here).

Putting new packing in isnt really that hard of a job. If you end up doing it, there have been several other posts you can refer to for guidance.

Keep us posted and dont be afraid to ask if you have any questions. I've found its a whole lot more time efficient to ask first rather than doing a job once, then asking why it didnt work, and finding out i'll end up having to do it all over again.

Cheers,
DKJ

[91 Sunsport]

Thanks for your help - I'll take a look and let you know.