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.

 

[Bobbywolf]

Digging this thread back up so if someone else runs into this issue, it can help them figure out what is going on.

Ok, so I dug my boat out of winter storage (The back yard, lol) and wanted to get it running because the first fishing tournament is coming up, and that will be my first boat ride of the year. I get it running on muffs, and again that rattle is present, and bugging the hell out of me. I pulled the lower unit, and ran the motor to confirm the rattle was gone, and it was.

It just wasn't sitting right with me, so I went ahead and drained the gear oil, which was brand new as of the lower end swap, and has no lake time on it at all. Only runs on muffs. I see fine metal. Not good.

More backstory, which I now know is relevant.
When I replaced the lower unit, I essentially made 1 from 2. My old bearing carrier was in much better shape, so I reused it, along with the reverse gear because I didn't want to press it out. (You may see where this is going).

Long story short, I had used the new gearcase, driveshaft, pinion and forward gear, with the old bearing carrier/reverse gear. My thought process is that reverse hardly gets used, so why worry about any previously worn in pattern.

Anyways, I pull it all back apart, and this time remove the reverse gear/bearings from both the old and the new carriers and place them side by side. It was now blatently obvious what was going on. The "Old" reverse gear was 22 teeth. The "New" reverse gear is 26 teeth! The crazy part is that even though reverse and forward gears were different tooth counts, they both meshed well enough with the pinion that I questioned if anything was even wrong. Obviously I caused this, but I would have thought I would have bad binding and big issues mish-mashing gears like this.

So finally I have an understanding of the issue. My "Old" damaged lower end was 1.83 gear ratio (12 & 22 tooth). My "New" donor lower end was 2.00 gear ratio (13 & 26 tooth).

I can no longer locate my old pinion, so I am forced to put this back together with the 13/26 gearing, in my old bearing carrier, stuffed into the new lower unit. I'll be doing this tomorrow, and I hope it works out. Fingers are crossed, and I will update when its complete.