Lower unit noise investigation

[Bobbywolf]

Looking for a bit of insight, input.

2004 2stroke Merc 40hp ELPTO

I recently replaced the lower unit with a parts one, and it all seemed in excellent condition. Upon installing it onto the power head and running it, I can hear a noise coming from the lower unit in neutral. At first I thought I was partially in gear, but I was able to rule that out by playing with the shifter. It makes a growling/rubbing noise at all times it seems. (On muffs by the way)

So I wanted to get this outboard good for the spring, so I tore into it. I pulled the bearing carrier fully expecting to find metal, or at least a bad bearing. I found none. I then pulled the pinion and bearing to inspect those, and again, everything is smooth and perfect. I reinstalled the driveshaft and torqued the pinion nut down. The case is empty except for the forward gear and pinion in place, and my noise happens only when pushing down on the driveshaft. If I spin the driveshaft while pulling up on it (seating the pinion bearing) it spins smooth and silent.

I then went to my old lower unit with the broken driveshaft, and it does the same. Feels bumpy and noisy while spinning the shaft, unless I pull up, and it goes away.

Am I overthinking things here? In the water, everything would be loaded pushing the bearings into their cups, so I guess there would be no noise. I just do no remember this noise when running on muffs before.

Any thoughts before I finally put this thing back together and just run it? I can find nothing wrong.

 

[Chris1956]

The driveshaft bearings on a lot of Merc gearcases are cone shaped. The cones can face up or down. Some that face down have a spring and pin on the top end of the driveshaft to push them down into the race. Some that face up rely on hydraulic pressure to push them into the race above.

Since the driveshaft bearing is the highest one, if the gear oil gets low, they could suffer from lack of lubrication. You might doublecheck the bearing again, (replace it?) and make sure the gear oil is topped off. Growling is never good for gears.

 

[racerone]

Correct.-----You have to pull up on a driveshaft when testing for " noise " ----That is just the way gears work on these.

 

[Bobbywolf]

The upper driveshaft bearing is just a ball bearing style, and it moves smooth and looks perfect. The pinion, fwd and reverse bearings were all tested in their cups smooshing them together by hand and they were all smooth. Essentially the noise has to be the gear mesh when unloaded. There is no gear setup or shimming with this lower unit, so if it is assembled correctly, and the bearings are good, I have done all I can.

It is back together again. I'm going to run it. Thanks for the input guys.

 

[racerone]

The driveshaft is pushed up by the gears when working with a load.