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Intermittent high pitch whine at moderate throttle

H

HarryL

Member
Tohatsu MFS6B 2010.
started engine cold. I was running at medium throttle with a large load in the dinghy. i had been running for about 10 minutes when a loud hit pitched whine / screeching started. It seemed to be coming from under the cowling. I slowed, put in neutral and shut down. i did not remove the cowling but checked the prop for fishing line. All seemed clear. I restarted and no longer had the noise. I continued at a slightly more moderate rate for another 5 minutes to complete my trip. No recurrence of the noise. I checked oil. It was low but still at the dipstick so I topped off.

A few hours later I used the engine for 10 minutes at medium throttle with no noise. Power seemed fine.Shut down. Finally once more I used the engine at medium throttle (started cold) but after about 5 min the whine started. I just slowed to idle speed and the noise stopped And continued my trip for another 5 minutes. Dark so removing the cowling was not practical.

I am guessing it might be something related to the pull start but so far have not seen anything through visual inspection after removing cowling While running but without the noise. There are particles that look like belt dust seen on a motor with a belt driven alternator but this has been the case before so no new unusual accumulation as far as I can tell.

thank you,
harry
 
Thanks. for some reason my service manual is not here. Is the procedure straighforwad to remove the flywheel to inspect? And by straightforward are there any special tools Like a puller needed?
 
I have the harmonic balancer puller on and tight. I've been adding another 1/4-1/2 turn or so often but it isn't budging. I used a micrometer to try to get the device as close to even all the way around. I've seen vidoes of tapping with a hammer or getting some heat on it. Any suggestions to get it to release?
 
@pvanv Success with removing the flywheel. There was nothing under the flywheel, which I realize now would have been an alternator assembly, and this little engine doesn't have an alternator / rectifier. However looking at the magnet on the flywheel, the screws seem to have been worn down. Maybe this is part of the manufacturing process as I don't see the magnet being a replaceable part distinct from the flywheel itself. The igniter "pickup" might have some wear. My service manual (003-21034-2) has two different gaps specified. pg 5-47 says 0.5mm. pg 8-6 says 0.2-0.4mm. I used a piece of flexible material that measured 0.3mm and tightened the igniter. I'm not sure how it would have ever slipped to rub, then stop rubbing, if that was the problem. I will reassemble and test.3729D676-3568-4407-87BA-B3854CBF1427.jpeg9BF2C634-7A88-4C04-AC8D-67D67DDCD5B7.jpeg
 
Yes, the magnet is not serviceable separately. anthing around 1/2 mm or a little less is OK. Maybe some debris got in between?
 
Turns out it isn’t from the power unit but below it. I had hoped it was from not greasing the grease points in a while but not that. Noise stops when put into neutral which is new in that usually just slowing the engine made it stop. I changed the lower unit gear oil and it is milky. I can’t get it serviced immediately and it has been better but has started again after running for 10 minutes at half throttle. I will run slower for the next day or two until I can pull it out and get it serviced.
 
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