05 90 lower unit rebuild

[bottomfishin]

I have a yamaha 90 hp 4 stroke. The lower unit went out (still don't know the cause but broken teeth on the forward gear was result.) had oil in it, no water, but upon disassembly it seemed to me that the backlash was way to tight. I will correct that later. Upon installation of a new drive shaft bearing, the lower needle bearing, not the thrust, I noticed it drove in VERY tight. I used a tool I made for this purpose as I am a machinist and did not damage the bearing. After locating the bearing to the proper depth I tried the shaft, it has to be tapped lightly into the needle bearing with a soft blow hammer, shaft does not spin free. Could the bore in the housing be to small, causing the bearing to compress to tightly? I will measure bore size tommorrow and compare bearing O.D. but does anyone know what Yamaha's spec is for this bore? Also can the backlash be adjusted using the shims under the top bearing only? Thanks

 

[robert graham]

Re: 05 90 lower unit rebuild

my Clymer Yamaha Manual has specs for those gear backlashes which have to be adjusted with shims. I'm sure it has to be assembled just right, but it's more than I would try to tackle. A machinist like yourself will probably do better. Hope you have good luck!

 

[bottomfishin]

Re: 05 90 lower unit rebuild

Thanks Robert,,, I think I can get it done but still, it's pretty involved...just gotta be patient. The book isn't really clear on shimming however, just telling you to be sure to replace them like they come out.. however I suspect someone has be at this unit before and got them wrong. As I said earlier, the lash was non-existant when I disassembled.