Chirping noise at idle

[bman5150]

Last Fall, I had one of my two alternator bolts break. Unknowingly, I ran around and used the boat for at least 3-4 fishing days and miraculously the accessory belt stayed on and I didn’t break the other bolt.

my local Merc mechanic was not able to get the old broken bolt out of the flange it is screwed in to, so he thru-bolted it and installed a new accessory belt for good measure even though the old belt looked OK.

Ive used the boat 4 times so far this spring since that repair. Yesterday, I noticed a chirping noise from the motor. To me, it sounds like a bad bearing on a pulley. The noise disappears as soon as I touch the throttle. I removed the cowling while I was on the water and started the motor to see if I could determine where the noise was coming from. It seems it’s coming from either the alternator or the nearby tensioner pulley.

question 1 - at idle, the alternator isn’t engaged. In other words, the pulley of course was being turned at idle but I could see the coils stationary inside the alternator. Is that normal?

Question 2 - given that the noise disappears at anything other than idle, is this a clue as to what it could be? Any other thoughts?

question 3 - how difficult is it to remove the accessory belt? Figure I could remove it and see how each pulley turns and find the issue that way possibly.

Im modestly mechanically inclined and have done lots of work on car engines but only have dug around a little with my Merc. I’m concerned that I may have a long wait for service due to this covid mess but will likely call my local Merc mechanic when they open Tuesday to see if they can take a look. I just want to self-troubleshoot a few easy things prior to taking it in.

[bman5150]

Update:

alternator bolt broke again. Also discovered that ground wire attached to the other mounting bolt was broken. I

I’ve removed the alternator and I’m going to replace the ground wire and the broken mount bolt. This time, I’m going to use a washer on the bottom side near the locking nut.

Since I removed the good mounting bolt and it uses a locking nut, I’ll replace that as well.

Don, I think I need that locking nut and a new ground wire. I’m afraid the remaining wire might be a bit too short and would just break again from vibration. On the Merc 175 Proxs flywheel/alternator parts diagram, I need to buy part #11 (ground wire) and part #9 (locking nut).

Do you have these in stock and how quickly could you send them to me? Alternatively, I could probably buy a new locking nut at the hardware store and make my own ground wire with two crimps but what gauge wire should I use?

[bman5150]

Update:

I went to the hardware store an bought a grade 8 bolt, locking nut and loctite. Re-installed the broken alternator ground wire and installed the new alternator bolt. I torqued the bolt down to 40 lb-ft. Bounced around a local lake all day yesteday and no issues. The motor seemed to be even more powerful for whatever reason -maybe it was the broken ground wire causing an issue or maybe it was just that the air temps were only in the mid-40s, lol!

[moetorola]

question 1 - at idle, the alternator isn’t engaged. In other words, the pulley of course was being turned at idle but I could see the coils stationary inside the alternator. Is that normal?

That does not sound normal at all, sounds like the belt is slipping on the alternator from not enough tension. I would replace belt, also!

[bman5150]

Thanks for your response, but the alternator pulley turns perfectly fine now. Belt looks great (it was new this spring and never slipped off even when one of the alternator bolts broke again. Motor ran great all day in the cold Saturday. Pulled the cowl and inspected the new alternator bolt-all buttoned up. I think the dealer simply way over torqued the new grade 5 bolt. My guess is even the grade 5 bolt would work fine provided you didn’t over-torque it.