Alpha Drive Prop Shaft Tolerance

"Year 2000 outdrive. I noticed

"Year 2000 outdrive. I noticed that with drive in gear with no prop on shaft, there is a small amount of concentric movement. What is the tolerance for this?? Is there a possibility that a previous owner has bent the shaft?? Drive appears in good physical condition otherwise (no skeg damage). Thank you for any insight."

If you can see the movement it

If you can see the movement it is past any tolerance level and should be replaced. Just be sure you are not judging this by the very end of the shaft while looking straight at it. The end of the threads can make it look as if the shaft is bent while turning. If the shaft has any movement on the side of the shaft then it is bent. You may get away with a one or two thousands of an inch but that is it. Anymore will cause the shaft to be out of balance and cause damage to the lower gear case over time.

"If you look at the center, wh

"If you look at the center, where the lathe spindle went for machining, you'll see if it's eccentric or not. Ideally, the shaft will be out when checking for bends and a dial indicator used. IIRC, .003" is the maximum.

To answer your question, yes, it's possible and if there is any indication of repainting on the cone or skeg, it's probable that the previous owner hit something."

"Let me say this... If you ar

"Let me say this... If you are close to tolerance as measured with a dial indicator, you might consider putting together and going boating. Likelihood is that you wont notice much. That and replacing the shaft will cost almost as much as buying a new lower unit. The worst that can happen is that it further ruins the lower unit over time (bearings and seal)... and its already ruined."

"Replacing a prop shaft isn&#3

"Replacing a prop shaft isn't that bad. I bought a used one on ebay for $80 including shipping and it was straight. The hard part is having access to the specialty tools needed. Also, shaft deviation (behind the bearing) is taken up by the flexible seals. If it hit anything hard enough to bend the shaft too badly, the bearing and/or carrier will also have issues. I've seen people go for years with bad seals and all they did was change the gear oil frequently. OTOH, when I finally opened one of them to replace the water pump ass'y, the drive shaft, prop shaft, bearings and gears were pitted (pretty badly) and the drive shaft needed to be replaced, but the wear was, surprisingly, not as bad as I would have expected.

If the prop is installed and the shaft is bad enough, the hub will rub on the gear case where the prop fits in (the shoulder on the prop).

Go boating!"

"I felt certain that the smoot

"I felt certain that the smooth side wall of shaft was moving by eye, and by feel. Nothing more scientific. And movement was eccentric (sorry!)to the center line of shaft rotation. I figured the tolerance for movement would be in the thousandths of inch. Let me put prop on and look at clearance of prop hub to case over weekend. I'll update early next week. Great quick feedback guys."

"The tolerance at the forward

"The tolerance at the forward end of the splines is .007 on alpha,mr,#1 drives and .005 on gen 2 alpha. That shaft would be way past any tolerance if the prop barrel rubbed the housing. If you can visually see runout in the center drilled portion of the shaft, its junk."