Shaft Alignment Tolerances

[racclarkson@gmail.com]

On my last cruise, I picked up a vibration on my port side above 1,000RPM. There is no indication of striking anything or apparent prop damage. My cutlass bearings were inspected OK at last haul-out in May; I had a small ding repaired and port prop successfully balanced at that time. There is no indication of gear issues. So, I'm going in two directions. I'm going to break the shaft/gear coupling and check the alignment because I've always had just a bit more vibration (well within acceptable limits) on that side than starboard. I'm also looking at possibly a cylinder (injector) dropping out. I'll be looking at that probably before I look at the shaft, as I really doubt anything there has changed.

My question is this: What would we consider to be the allowable tolerance for shaft alignment? The shafts are 2-1/2", btw.

Thanks for your input.

[JD5652]

Not my area of expertise.... but there's a good current discussion here... and sounds reasonable..

https://www.downeastboatforum.com/threads/tolerenace-for-propeller-shaft-alignment.27046/

Fifth post down on that thread.... 0.001" for each inch of shaft diameter plus 0.002"...

Have you checked motor mounts?

[racclarkson@gmail.com]

Not my area of expertise.... but there's a good current discussion here... and sounds reasonable..https://www.downeastboatforum.com/threads/tolerenace-for-propeller-shaft-alignment.27046/Fifth post down on that thread.... 0.001" for each inch of shaft diameter plus 0.002"...Have you checked motor mounts?

Thanks, will check it out. Mounts are solid.

[dsharp]

.003 is considered the outer tolerance. I usually set the gap, if any, at the top since the mounts seem to settle more in the rear, over time.

[Briankinley2004]

Mine had a vibration and found about 10' of cast net rope with lead molded around it on the shaft.

[DCMY #92]

When you say "no apparent" prop damage. How did you inspect the prop? Did you measure the path of each blade against a fixed point?