1988 US Marine 125 rythmic knocking coming from what sounds like leg/lower unit?

[mike22ca]

I have a 1988 US Marine 125. The has been running great ever since i bought it earlier this year. On the way back into the dock the other day I slowed down to come into the harbor and as I was putting into the dock to pull the boat out I noticed a odd sound coming from the motor. Pulled it out and trailered her home and as soon as I got home put some ears on and fired her up to flush the motor and I can hear kind of like a rythmic knocking sound which seems like its coming from the lower leg area/lower unit. The motor goes into and out of forward and reverse gears perfectly fine no problem. I checked and changed the lower unit oil thinking maybe it was low... but it was full. No metal flakes in the old oil. Any idea on what might be causing this?

 

[NYBo]

Impeller?

 

[SkiDad]

with your engine off, does the prop make any noise when you spin it in neutral ?

 

[mike22ca]

NYBo - I was wondering if that was a possibility as well? Its never overheated on me so I figured it must be ok?

mitzysman - No noise at all. Spins nicely. Prop shaft is tight no movement etc.

 

[Jiggz]

I have the 89-125HP and yes there is rhythmic noise coming off the LU usually just above the bullet. And this is mainly coming from the upper drive shaft bearing which I believe is normal. However, if you think yours is loud enough to get your attention, the best diagnosis is to dismount the LU and then check for plays in the drive shaft, side to side and also up and down. If there is too much play, it would mean the bearing needs to be replaced.

 

[mike22ca]

thanks Jiggz I'll have to check it out... I'll have a week off next week so it'll gimme a chance to take a look. I hope its something simple. It STILL runs awesome despite the noise. I def noticed the noise when it started though.

 

[Jiggz]

Great! Just make sure the gear oil is filled up to the bottom of the vent hole. All bearings in the LU get their lube from the gear oil. And the reason the level of gear oil is critical is because of the location of the upper drive shaft bearing. As simple as getting air bound can mean disaster for the upper bearing. It is always recommended to ran the motor for couple of minutes in neutral, shut off and then let the LU to bleed off after filling by keeping the vent plug screw loose. And then tighten it only after checking the gear lube oil level to be at the bottom of the vent hole.

 

[mike22ca]

So it turns out that I have a chipped tooth off of my forward gear. Does anyone know where I can get one for a decent price? I saw a couple on ebay but I was wondering if I had any other good options?

 

[SkiDad]

easier to just change the whole lower unit and sell the one you have. I picked up a whole motor for 200 bucks on craigslist earlier this year - took off the lower unit and sold the engine for 180. I have seen some lower units on eBay too for around 300 which is better than i normally see them on there.

 

[mike22ca]

I dont know where you guys find all these cheap lower units at!!!! I checked out ebay and a few other places and they all seem fairly expensive. And the ones that are cheaper looks like crap. My lower unit other than the chipped gear is perfect, pressure tested no water intrusion, really good shape. Im still better off with a cheapy you think?