# Yamaha F40 Lower Unit Repair



## ek02 (May 8, 2012)

I am working on a 2006 Yamaha F40 that had a broken driveshaft. The shaft looked like it had corrosion or a bad spot that caused it to break about 12-14" from the water pump. The lower unit turned easily. The shaft bearing had .007 up and down end play. My question is should I shim the bearing to .007 end play or try to shim it for zero end play? Since it was working fine before the shaft broke, shimming to zero may cause the gears to mesh differently. Anyone have experience with this?


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## jmrodandgun (Sep 20, 2013)

ek02 said:


> The shaft bearing had .007 up and down end play.


Thrust bearing?



ek02 said:


> My question is should I shim the bearing to .007 end play or try to shim it for zero end play?


Pull the FSM and see what the end play should be on that bearing. Setting a thrust bearing to zero will end poorly. You need that end play for lubrication and thermal expansion. Also the way the gears are cut they push up on the pinion and shaft when under load. If you set your end play too tight the gears will not mesh. Sometimes you can feel the difference by pulling up or pushing down on the shaft while turning it by hand.

Someone will need to confirm this because my memory has gone to shit....


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## Guest (Mar 31, 2019)

jmrodandgun said:


> Thrust bearing?
> 
> 
> 
> ...


Couldn’t have said it better!


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## ek02 (May 8, 2012)

The .007 play was up and down movement on the shaft. The case has to have some wear on it to get that loose, since the pinion pushes up on the shaft. The service manual procedure uses a special tool to measure the distance from the bottom of the bearing cup to the top of the pinion gear using a nominal shim, and it says to get as close to zero as possible, but I agree with jmrodandgun that zero would be too tight. I may try for a shim pack that gives me .003 or so. The new bearing is the exact same thickness as the old one. I don't have the shaft yet, but if it measures the same as the old shaft, I think I can reduce the shim pack a few thousands. I have a good selection of shims. Hopefully the gears will mesh like they used to. Everything else looks good. Just had a hard time getting the bearing carrier out with a home made puller. All the seals will be replaced of course.


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## ek02 (May 8, 2012)

I got the new shaft today and the distance from the top of the pinion gear to the upper bearing flange is exactly the same as the old one 9.665", my new bearing and race measures the same as the old one, so I should be good to go with a little thinner shims. The shop manual shows the prop shaft and driveshaft seals with the lips pointed toward the water. The seals I took out had been replaced and were put in with one lip to the inside and one to the outside, which is how Evinrude/Johnson always did it. I guess it's better to leak some oil than to get water in the lower unit, so I will probably go with Yamahas shop manual way.


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## ek02 (May 8, 2012)

I got the shaft in and shimmed today. It has .002" end play and the gears mesh ok.


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## ek02 (May 8, 2012)

I finally got around to finishing this project. The lower unit went together ok and I removed the powerhead to get the upper part of the broken shaft out and to replace the teflon bushing in the mid section. There was a lot of corrosion in the bushing area. It runs fine and the lower unit works well. Attached are photos of the shaft. My guess is the shaft may have cracked and then corrosion started, causing the shaft to break. The lower unit bearings and gears all looked fine except for pitting on the upper shaft bearing and race. Any thoughts on why this happened?


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