Yamaha 8HP 2-stroke squealing sound

[Kiwi_Wil]

Hi all, I have a 2000 Yamaha 8HP 2-stroke. It's a tidy motor that starts and runs well but occasionally it will make a horrible squealing noise. Check out the noise in this video:
https://youtu.be/TO16SNMxXrA

Here's what I know so far:
- The noise only occurs after at least 20-30 minutes of hard running
- Sometimes the noise will go away if you hold a certain RPM but it generally stays across the whole RPM range and gets louder and higher pitch with increasing revs
- Stopping the engine, waiting a few minutes and starting again can sometimes fix the noise (for a while)
- It sounds quite unmuffled, so less likely to be coming from deep in the engine or below water line
- I recently removed the thermostat, there's no evidence of the engine overheating, the tell tale is usually just slightly warm
- The motor still runs ok with the noise, but I noticed it's slightly harder to start if you stop it during it's noisy state
- I thought it might be a worn driveshaft bushing but there's no evidence of wear on driveshaft from bad bushings

Any ideas would be appreciated before I tear into it. Thanks

[TownsendsFJR1300]

IF there is a drive shaft bushing, have you re-greased it and the shaft?

[robert graham]

Check your prop for possible contact with lower unit case….possibly due to the wrong thrust washer in front of prop….

[99yam40]

did this noise start after you removed the thermostat?
or was it happening before you removed it?
Since it sometimes changes when restarting, make sure the starter is not hanging up in the flywheel

either way you really need to put a good stat back in so the proper back pressure will cause proper water circulation throughout the motors cooling system

[Kiwi_Wil]

Thanks for all the suggestions.

I bought the motor recently and serviced it before I even used it. I noticed the thermostat was seized partially open. I bought a Sierra replacement which didn't fit... then went to a boat shop to get a genuine replacement but the dealer advised me they usually remove the thermostat from the 8 as they are prone to blocking up. I took his advice and ditched mine, then the noise occurred on my first outing.

Sounds like I should put a genuine stat back in and go from there. At least my motor will be running at the proper temp.

[TownsendsFJR1300]

Have you serviced or at least checked the water pump?

It may or may not be the issue but the much smaller engines, like yours, that sit, the impeller comes apart.

Check the lower unit oil as well...

[99yam40]

run the motor with the cowling off and see if the sound is louder and make sure the starter gear is dropping away from the flywheel when the noise happens