Default Knocking / rattle sound in 40hp outboard - Lower leg?

[Zacchini3]

Hi,

I have this old 1993 40hp 2-stroke Yamaha. It has been sitting on an outboard stand for a couple months. Started it up on the weekend and it was making a horrible knocking sound which gets worse at lower idle (see videos 1 and 2). When it was on the boat I bought I don't remember it having that sound but it is quite noticeable now.


I took the lower leg off to see if that stopped the knocking sound and it seems like it has? (see 3rd video). I think it has but someone else said they could still hear it. Once the leg was off I noticed the gear linkage is quite loose and when I move it around it rattles, so I was thinking maybe that was the issue... (videos 4 and 5)

I've created a public onedrive folder which has the videos in it:
https://1drv.ms/u/s!Am6rrabP1B2pk13-...LTdVu?e=qGnyqM

Wondering to hear your thoughts. Hope the videos are clear enough

Cheers

 

[Zacchini3]

"Default" is not supposed to be in the title

Any ideas anyone?

 

[robert graham]

Drain lower unit lubricant to inspect for metal particles, water, corrosion, etc.

 

[racerone]

Shift linkage is not the issue.-----Check spark on each lead.-----Possibly running on 2 cylinders.

 

[Zacchini3]

Shift linkage is not the issue.-----Check spark on each lead.-----Possibly running on 2 cylinders.

Just checked spark and compression this afternoon. All 3 cylinders have spark and compression is ~100psi on all three cylinders

Drain lower unit lubricant to inspect for metal particles, water, corrosion, etc.

Already checked the gear oil and changed it, nothing of significance to report.

Sorry for the late reply, working full time now and super busy
Cheers

 

[OldButSlow]

Just checked spark and compression this afternoon. All 3 cylinders have spark and compression is ~100psi on all three cylinders


Already checked the gear oil and changed it, nothing of significance to report.

Sorry for the late reply, working full time now and super busy
Cheers

This is not in the vicinity of the lower unit, but I had an Evinrude v-4 that developed a very audible rhythmic tapping noise at idle and it seem to go away as the rpm's came up. It was similar to a valve tap noise in a car engine. It was very difficult to discern where the noise was originating. Being a 2 stroke, I was afraid it was a crank bearing. It turned out that one of the reeds was cracked and the loose edge was tapping the reed cage with every intake stroke on that cylinder. Luckily I discovered it before the loose piece of the reed/leaf came off and travelled into the cylinder. Just something to maybe rule out.