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 Post subject: Chasing a noise by alignment and prop shaft troubleshooting
PostPosted: Fri Jun 05, 2020 10:54 am 
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Joined: Mon May 13, 2019 2:29 pm
Posts: 5
Boat: 2011 Axis A20 with 105 hours (Purchased last year with only 76 hours!). I didn't find a good reference here for what I am going through, so I though I would post about me chasing my tail as I go so it might help someone else:
A while ago, I...(I mean my wife, right?) didn't see a piece of mostly submerged wood on a choppy day and struck the prop. I had a vibration afterwards and I wanted a spare prop for longer trips, so I bought a new prop and will repair the other since the damage was minimal, but enough. This fixed the problem, or so I thought until I pushed through some other surf waves at surf speed and when going 30 mph+; both of these scenarios cause a temporary slight humming sound, but no vibration that is noticeable to me driving the boat. The sound is small enough that my wife thinks I'm hearing things, but coming from a virtually flawless boat, it bugged me. I thought I would check engine/vdrive alignment as well as issues with the drive shaft and cutlass bearing, shaft log, etc. I stuck a medium sized zip tie around the shaft through the log from under the boat, and it seemed to be tighter at the bottom. I checked alignment on the trailer, then in the water for a more accurate reading and noticed that the gap was about 2 thousandths different in the water, so if you're shooting for .003, it seems like measuring in the water is worth the effort. I needed to lift the motor some as there was now about +5 to 6 thousandths gap at the bottom of the coupler.
I had some trouble getting access to the jam nut on the motor mounts and I have a decent set of tools. The nut looks easy to get to, but it is shrouded from the sides and the top just enough to limit clearance and the motor blocks the other side. I ended up getting a 15/16" crowfoot flarenut wrench and was able to use a 1/2" to 3/8" drive coupler as a really small extension attached underneath the wrench because it is shrouded from the top. Any other, including different sized crescent wrenches wouldn't fit because of how the nut was oriented. I think an open end flex tip wrench might be the best, but most flex at the box end, and I couldn't find any the right size. I asked my local dealer service tech how they adjust those and he said they cut an open end wrench in half. Once the jam nut was loose, I put a strap under the vdrive and hoisted with maybe 200 lb's of upward pressure to a lift setup I have in my garage to make turning up the motor mount easier. This seemed to work as the following adjustments only took about 10 minutes total. I didn't know how much I needed to move the motor up, so I indexed the top of the motor mount bolts and made 1 complete clockwise turn (the crowfoot wrench came in handy again being able to watch the progress as it turned. This ended up being way too much as my gap ended up at the top after re-examination. It's probably going to be different for everyone slightly, but my experience seemed to be about 2-3 thousandths of coupler adjustment for every quarter turn on the motor mount bolts. I kept about .002 off what I predicted what being in the water would do to the gap.
I need to head back to the lake now, remeasure, and see if any progress has been made, but I wanted to start here before I forget important steps.
If anyone else has had similar symptoms and has any advise, I'm totally open to good advise. The shaft is perfectly centered in the cutlass bearing with no play or uneven wear. My next check will be to do a tape and wire test on the shaft on both sides of the strut to see if the shaft is bent. Nobody wants their shaft bent, right?


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