Vibration Problems

[87SupraCompMN]

Hello,
I have a 1987 Supra Comp ts6m. I was having vibration problems when I ran the boat real slow or putting it into nuetral. I took the tranny out and rebuilt it...bearings, clutch plates, etc...although everything looked pretty good. We put it back in and are still having the same problem. It's aligned pretty close so I don't think thats it. I ran a dial indicator on the shaft and spun the shaft one full turn several times and it varies .010 of an inch. I would think this is a sign that its bent. The other thought would be maybe the damper but I was told those don't go bad too often. Also, if its the shaft, does anyone have the specs on the shaft as far as length goes? I know its one inch in diameter but I don't know the lenght and I would like to order one before I take it apart. Can anyone help me on this one?

[DKJBama92Mariah]

.010 is a pretty high runout. I have been told that factory specs call for runout of <.004. Personally, I would pull the shaft and take it to a machine shop and have them check it. If you can get the shaft off without destroying the coupler, many shops will offer to cut you a new shaft. That's what I'll do the next time I bend my shaft. I keep my money local if at all possible.

[87SupraCompMN]

Thanks, yeah I heard about the same for runout. I should probably replace the strut bearing while I'm at it...it seems pretty tight when I turn it manually. Do you have any idea what the lenght on them are?

[DKJBama92Mariah]

Not sure on the length. Skier's choice could probably tell you.

The strut bearing should feel pretty tight when it's dry. It's only lubricated by the water flowing though it. I would be more concerned if the driveshaft turned really easily.

I would check to bearings to see if they're wearing evenly. If they are wearing like the shaft is running though the strut cockeyed, then the strut may be bent as well. I know of no way to check for a bent strut other than to just eyeball it. It takes a pretty good smack to bend a shaft like that, and the strut could also be a victim.

Do I understand you correctly that the vibration only occurs at low speeds? What about higher rpms? Does the boat shake?

When was the last time you had the prop in the shop for a pitch and balance? If there is a lot of trash in the water where you boat, all those little dings can add up. I get mine pitched and balanced every 2 seasons regardless of whether I hit anything big.

[michael hunter]

You said it vibrates in neutral. The shaft isn't turning if you want to prove its not the shaft disconnect the coupler from the trans. Are you sure you dont have a cylinder misfire?
Try pulling the spark plug wires off the dist cap one at a time while looking at the tach.
The RPMs should drop the same foe each cylinder. Note use insulated pliers to pull wires.

[87SunSportMikeyD]

Good luck! There are two 87 SunSports in Fridley, MN :)

[mapleleaf]

Not sure if this is your problem, I do hope it's mechanical, but if the cowl is shaking under this vibration situation, is there some chance that you could have rot in your stringer's and the boats structure is in question....
I know it's an ugly question, but it came to mind....

[87SupraCompMN]

I just pulled the prop and disconnected the shaft and coupler....still makes the same noise. Could it possibly be the damper?? I'm running out of ideas here.....

[87SupraCompMN]

Now that the tranny is rebuilt it's more or a clunking noise....its not that loud but its noticeable. I took the shaft off along with the coupler and its still doing the same thing....could it possibly be the damper??

[DKJBama92Mariah]

Not sure if this is your problem, I do hope it's mechanical, but if the cowl is shaking under this vibration situation, is there some chance that you could have rot in your stringer's and the boats structure is in question....
I know it's an ugly question, but it came to mind....

I think Mapleleaf may be onto something here. Before you spend the time to remove the tranny, put a socket wrench on the bolts holding the motor mounts to the stringers. If the bolts just turn freely in the stringers you have my sympathies.

[87SupraCompMN]

No its not rotted...checked that already. I actually pulled the shaft tonight and the clunking quit when I ran it....I think the shaft is bent or at least that what it looks like. I will install a new one tomorrow and let you know if what comes of it. Thanks for all the help!

[mapleleaf]

I'm with DKJ check dem der motor mounts......I got some rot and a little cowl vibration I notice at idle....not the end of the world, but I will have to do stringer's someday......