# Lower unit knocking



## Riledup (Jun 10, 2013)

So, I have a 2001 yamaha LF 115 TXRZ ( counter rotating) with a lower unit going bad. I have been looking around and haven't had much luck finding one for less than 1800 bucks. Apparently, this is a one-off gear case. Anyone know where I could find one or know someone who rebuilds them locally? I may rebuild it myself if I can source the parts on the cheap. I am pretty sure it just needs thrust bearings because it is just knocking and there is no metal shavings on the plug. Thanks for the help.
Brad


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## Sea-r-cy (Oct 3, 2007)

Knocking? Like it's jumping into and out of gear? Might check the linkage.


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## Snagged Line (Sep 30, 2007)

I had a disturbing noise on my HPDI 250 that turned out to be the prop chattering on the splines of prop shaft... Switched to different type hub and noise went away..... Thank you Ken at Prop Gods...


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## Riledup (Jun 10, 2013)

forgot to mention, I tested the linkage and even ran it while manually pushing the lever as far over as it would go and it continued to make the noise. I did test the prop from my other motor and it made the same noise as well. The sound is like a one-per revolution metal-to-metal knock. I got close to engine while it was running and it sounds like it is coming from the driveshaft near where it goes into the gearcase under the water pump. I have decided to take it apart and it it kicking my a#s! I have been a mechanic for almost 20 years and have never had something fight me as bad as this dang lower unit. Thanks for the help guys


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## Snagged Line (Sep 30, 2007)

Please say you know about the hidden bolt under the steering torque adjustment fin...( aka; fin thingy over propeller)...


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## Riledup (Jun 10, 2013)

LOL!

Yes I know about the hidden bolt. Thanks. I have had the lower unit off for a few days. My first challenge was the spanner nut that holds the propeller shaft bearing carrier. After I had to chisel the nut out, my next challenge was the bearing carrier itself. I now have the bearing carrier and propeller shaft out but haven't got the forward gear bearing out. Once I get the forward gear bearing out, I can make an assessment on rebuilding this one or buying a new one for 1800 bucks. Good times!


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## Deeplines (Sep 28, 2007)

I just noticed a weird knocking on one of my engines when put in gear at Idle. Goes away with any RPM's. Read my manual and noticed it should be inspected once a year. I've never taking the prop and spindle off to inspect but I guess I will soon. 

Please keep this thread informed on what you find.


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## Riledup (Jun 10, 2013)

Deeplines,
Run your engine and disconnect the shift cable from the lever in the engine compartment so you can push the shift lever manually into gear. Once it's in gear and knocking, push the shift lever farther in the same direction to see if the noise goes away. If that doesn't work, try a different prop on the problem motor to see if the sound goes away.

Took me 4 days, 2 home made special tools, and had to weld a slide hammer to the prop shaft to get my lower apart finally. Gears look fine, so I ordered a new clutch dog since mine had some wear on it. Going to change the thrust bearings and seals while I have it apart. Will update once I get it back together.


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## Deeplines (Sep 28, 2007)

If you need to use a press let me know. Looking in my manual you may need one. I have no hondas tbough.

I also suspect the clutch dog and bearings in my foot


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## GatorMcKlusky (Jul 11, 2016)

http://www.thehulltruth.com/boating...15-4-stroke-noise-low-rpm-stainless-prop.html

seems to be a common problem with the F115 a lot of people say its normal if it goes away with a slight rpm increase in forward.


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## Riledup (Jun 10, 2013)

Thanks Gator.
I would agree with you on the common noise with the smaller 4 strokes but mine has been getting louder and louder. For the first 1080 hours, I had no noise at all on either motor until recently. Like some of the posts say in your link, it is probably the pinion gear bouncing with no load. I am pretty sure mine is progressively getting worse and I wanted to address it before I had to buy a whole new lower unit. I tried the prop from my other motor and the noise continued as well.
I have ordered all my parts, around 700 bucks worth, but my order keeps getting delayed. Hopefully, will have parts in the middle of next week. Will update after I re-assemble and test my work.


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## Riledup (Jun 10, 2013)

*update*

After spending several hundred dollars on lower unit parts, I still have a very loud engine/lower unit. I replaced the driveshaft thrust bearings, forward gear thrust bearings, prop shaft axial bearing, clutch dog, shifter springs and misc. parts, and all seals. Apparently, everything I replaced had no effect on my problem so I am back at square-one. 

I have spoke to 2 marine mechanics about this issue recently and both think my problem is not the lower unit itself. Mechanic A thinks it is play or slop between prop and prop shaft or thrust washer causing it to rattle around. Mechanic B thinks it is my motor running poorly so it is under-powered until I increase the RPM's. I appreciate both of their opinions and help because I am starting to get pretty annoyed at this whole deal.

Today, I tried, yet, another prop on this motor with no change. I still need to measure the prop shaft to see if it is worn ( as per mech A). I, also, added B-12 fuel treatment ( as per mech B), cleaned and tested spark plugs, cleaned and tested fuel injectors, tested throttle position sensor, performed compression check, and started on syncing up the throttle bodies when I called it quits for the day. All of the tests I performed have passed except for one odd issue I just found.
I don't have any of the fancy yamaha tools to complete the throttle body synchronization so I just use old fashioned vacuum gauges and a multimeter.
While trying to match up the vacuum readings on all four cylinders, I found that the number two cylinder vacuum reading was steady at 15 in Hg while the engine was at idle. The other three cylinders vacuum readings were all fluctuating back and forth approximately between 5-20 inches Hg of vacuum at idle.
so...............................any thoughts?
Any yamaha techs on here?


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## Riledup (Jun 10, 2013)

Here is a short video I took.


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## holicori (Dec 26, 2012)

Not sure on outboards, but for cars...a vacuum shouldn't be as low as 5hg. Should be around 15-18hg and stay in that range. 

Sent from my XT1254 using Tapatalk


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## Riledup (Jun 10, 2013)

*progress?*

I checked everything everyone recommended and whatever else I could think of on the port engine and lower unit. The only improvement I could notice in the port lower unit I changed the bearings in, is the prop shaft end-play is in limits now, (.010"),where the starboard lower unit end-play is out of limits. I have adjusted the vacuum and TPS sensor before but did it again and again until I got it dialed in the best I could. The shop manual says to match up the vacuum between the cylinders at idle with 1-3 cm which is a PITA with the gauges bouncing so much. Since I wasn't having any luck, I decided to make adjustments and then rev up the engine until the vacuum stabilized, around 2000 RPM at 16 cm of vacuum, to make sure they were matched up. I was able to get the cylinders with 1 cm of vacuum doing it this way and the motor idles smoothly and throttle response it crisp now. The knocking continued on the muffs but wasn't as loud as before.

Finally, took the boat out again yesterday to do some diving and run the engines to get the fuel treatment run through them. 
When we first launched the boat, there wasn't much change in the noise with either motor in gear at idle. After running the boat offshore 25 miles at cruise, I checked for the knocking noise again in the port motor, and now it only did it in reverse. Around mid day, the noise was all but gone on the port motor in either gear!
Apparently, mechanic B was correct. My motor was running so poorly causing the noise which resonated down to the lower and driving me nuts. 

Now, the starboard motor is making noise as well but it isn't as bad as the port once was. I plan on matching the vacuum like I did on the port motor and hopefully that will be an end to my headache with the boat......for now. 

Thanks for everyone's help on this project.


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## Emerald Ghost (Mar 11, 2008)

You're one heck of a mechanic !


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## Deeplines (Sep 28, 2007)

Wish I could have been there to see that. That sounds WAY over my head if that is the knocking sound I hear coming from my foot. My sound does go away completely at 1500RPM and only when in gear.


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## kanaka (Oct 3, 2007)

I remember trying to sync a 4 cyl jap bike eons ago with a homemade gauge using tubes and mercury. Worked nice till I blipped the throttle, all the mercury was gone. Didn't feel like buying more thermometers.


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## Riledup (Jun 10, 2013)

Deeplines, 
If yours sounds like mine does on the video then that is probably the problem. Now that my port motor is running right and not making any noise, at idle it is smooth and doesn't shake like it did before. May be something to look at on yours. I remember when I first got these motors with only 200 hours on them they didn't shake at all or make any noise, I had turn around to make sure they were still on because they were so quiet. If you rule out all the easy stuff and you still have problems, let me know, we can work something out to try to get you running right.


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