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Author Topic:   Yamaha F115 Gearcase Repair
onlyawhaler posted 07-18-2010 03:11 AM ET (US)   Profile for onlyawhaler   Send Email to onlyawhaler  
I have twin 2006 Yamaha 115 EFI four-cycle motors on our houseboat at Lake Powell. One has started leaking oil around the shaft on the gearcase. This started after a alummium prop was damaged and replaced and run with an improper thrust bearing by accident. Because of the cost of pulling out the entire houseboat, it would help to just remove the gearcase and work on it that way and leave the boat in the slip with the Whaler. Four bolts hold on the gearcase on this Yamaha motor. Is it as simple as removing those bolts and the lower unit just comes off or is the gearcase attached in other ways?

Is the rear seal that I can see with the prop removed something I can replace on my own or is it a lot more involved and needs special tools? Thanks for any advice


jimh posted 07-18-2010 09:32 AM ET (US)     Profile for jimh  Send Email to jimh     
Typically there is often a hidden bolt that is under the zinc sacrificial anode and trim tab. Yamaha copied much of their gear case design from Mercury, and this hidden bolt is common on Mercury gear cases. If may also be necessary to release the the shift shaft from the power head, if the shaft is retained. Some shift shafts are splined and are not retained.

I am not familiar with the process of replacement of the rear propeller shaft seal on your engine. Perhaps someone else can give the details of the procedure to replace the rear propeller shaft seal. Typically to proceed at any depth into the gear case internals you will need specialized tools.

conch posted 07-18-2010 09:44 AM ET (US)     Profile for conch  Send Email to conch     
I believe more than four bolts hold the lower unit on, more like seven or eight need to be removed. Once the lower unit is down if [you are] not comfortable changing the seal, take it to a shop. You will have done most of the labor, and they can perform leakage tests after the seal and any other parts are replaced. Then you put the foot back on your motor.

An exploded parts view is available online at [did not give any URI but mentioned the word] Yamaha or [the domain]


outragesteve posted 07-18-2010 02:17 PM ET (US)     Profile for outragesteve  Send Email to outragesteve     
Your seals may be damaged along with the bearing carrier. The proper way to replace the two seals requires removal of the bearing carrier. I'd suggest removing the gear case and having your dealer inspect the carrier. If the wrong thrust washer was used it may have worn our the casting, not allowing the seals to keep oil in and, just as important, water out. There are six bolts on the side of the gear case and one under the trim tab. The gear case will slide off. The shift shaft and water tube simply slide off the gear case when it is droppped. If your speedometer pick-up tube is connected, disconnect it at the lower unit first. Also make sure shift control is in neutral for alignment. Good time to do a water pump service! Good luck
onlyawhaler posted 07-18-2010 02:42 PM ET (US)     Profile for onlyawhaler  Send Email to onlyawhaler     
Thanks for the help everyone


jimh posted 07-18-2010 04:54 PM ET (US)     Profile for jimh  Send Email to jimh     
Removal of the gear case is much easier than reinstallation of the gear case. Gravity helps during removal, and all the couplings are being taken apart. During reinstallation you have to re-align all the couplings and fight gravity. Good luck.
outragesteve posted 07-18-2010 10:09 PM ET (US)     Profile for outragesteve  Send Email to outragesteve     
This is much easier when the engine is full tilted up. Try to keep the unit "square" until the drive shaft clears the mid-section. Good luck!

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