what causes this type of where on the lower input shaft

[lime4x4]

I have a 1986 mercruiser alpha drive. I replaced the upper unit 2 years ago with a stern drive engenering unit. The other day i had an issue with the drive and took it apart.I found this weird wear pattern on the shaft

 

[picklenjim]

Re: what causes this type of where on the lower input shaft

Worn coupler.Probably should have been replaced with the drive if you didn't.Or possibly miss alignment.Either way you need a new shaft now.

 

[Don S]

Re: what causes this type of where on the lower input shaft

Lack of lubrication. Those splines should be greased each time the impeller is checked or replaced. Which should be at least every other year.

 

[lime4x4]

Re: what causes this type of where on the lower input shaft

the shaft was greased last fall when i installed a water pump impellor in the lower unit