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Old 03-05-2016, 19:08   #1
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Minor wobble of prop shaft

I was just getting ready to adjust / tighten the stuffing box nut, and when I engaged the marine gear I noticed a minor wobble in the shaft. Is "any" wobble OK? I've read this could be caused by the the shaft connection to the marine gear???? any help appreciated.

Mike
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Old 03-05-2016, 22:39   #2
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Re: Minor wobble of prop shaft

There should be a specification listed somewhere... generally I'd expect it to be too small to be easily seen. Some number of thousandths of an inch. (or tenths of a thousandth of an inch... or the metric equivalent)

You'll have to list the exact equipment involved for someone to look up the tolerance for your installation.
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Old 04-05-2016, 00:13   #3
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Re: Minor wobble of prop shaft

I once thought mine surely must be bent, considering the movement observed.

At haulout I wasn't surprised a new cutlass bearing was needed as I could hear it while running. But I was surprised the shaft was not bent. The engine was so badly mis-aligned the the shaft was flexed to the point of an observable wobble.

The shaft and coupling went to the shop for a keyway repair and the coupling flange needed the face surfaced some to true it to the shaft.

Back in the water I carefully aligned the engine and all is well since.


I would think you shouldn't be able to see any wobble and the coupling connection could cause it, either by engine alignment or coupling flange trueness.
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Old 04-05-2016, 03:28   #4
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Re: Minor wobble of prop shaft

I believe the tool for measuring this is called a run out gauge, or a dial indicator gauge. It's essentially a version of a dial caliper, which instead uses an indexed tip that continually bears on the shaft as it turns. And the part which bears on the shaft is connected to a dial which measures things. So as to tell you how far things are, or aren't out of true.

My description of the tool is lacking in eloquence & descriptiveness, but hopefully it makes sense. Any professional who works on these systems can help you with this. Meaning, both providing the tool, & doing the measuring for you. Though they're not complex. Have a look via YouTube.

Regarding your drive train. Have you checked each of the connections in it, starting with the engine, & going all the way to the propeller? As if any one of them is loose, improperly torqued, or worn, then it could cause your problems.
So could worn engine mounts, or a misaligned engine. Ditto the other causes mentioned herein, as well as an out of balance, bent, or worn propeller.
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Old 04-05-2016, 05:00   #5
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Re: Minor wobble of prop shaft

Mike,

Where exactly do you see the wobble??? At the stuffing box?

I suggest you have your cutless checked, as the small clearance fit there should not translate to noticeable movement further up the shaft...

Unciv has a good description of it... there are specs for tailshaft runout... (tranny output shaft) I wouldn't expect you could see this with the naked eye... we're talking 0.005" from memory of "something of mine"
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Old 04-05-2016, 05:44   #6
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Re: Minor wobble of prop shaft

Good advice using a dial indicator to check the run out. However if you can see the wobble, there is something terribly wrong, and using your boat as us will most certainly cause you additional issues and cost you more money in the long run. If there is wobble, there is vibration throughout the drive system and that can and usually will cause excessive wear on your gear. Especially the tail shaft section. IMO, the shaft needs to come out and be checked out as well as the cutless bearing. I'd also remove the shaft coupler section that goes into the back of the gear and check the spline for wear as well as changing the seal. I say this because this same issue and my lack of understanding left us bobbing around for two days during a circumnavigation waiting for wind after loosing the gear due to a "slight shaft imperfection"
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Old 04-05-2016, 06:16   #7
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Re: Minor wobble of prop shaft

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Originally Posted by Jsta_Rebel View Post
Good advice using a dial indicator to check the run out. However if you can see the wobble, there is something terribly wrong, and using your boat as us will most certainly cause you additional issues and cost you more money in the long run. If there is wobble, there is vibration throughout the drive system and that can and usually will cause excessive wear on your gear. Especially the tail shaft section. IMO, the shaft needs to come out and be checked out as well as the cutless bearing. I'd also remove the shaft coupler section that goes into the back of the gear and check the spline for wear as well as changing the seal. I say this because this same issue and my lack of understanding left us bobbing around for two days during a circumnavigation waiting for wind after loosing the gear due to a "slight shaft imperfection"
WELL SAID! I was thinking along the same lines.
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Old 04-05-2016, 08:24   #8
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Re: Minor wobble of prop shaft

Also check your engine mounts. Worn out mounts can let the engine move around which translates down to the shaft. Should be no "bounce" to the engine when running under load.
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Old 04-05-2016, 09:18   #9
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Re: Minor wobble of prop shaft

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Old 04-05-2016, 09:28   #10
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Re: Minor wobble of prop shaft

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Originally Posted by Jsta_Rebel View Post
Good advice using a dial indicator to check the run out. However if you can see the wobble, there is something terribly wrong, and using your boat as us will most certainly cause you additional issues and cost you more money in the long run. If there is wobble, there is vibration throughout the drive system and that can and usually will cause excessive wear on your gear. Especially the tail shaft section. IMO, the shaft needs to come out and be checked out as well as the cutless bearing. I'd also remove the shaft coupler section that goes into the back of the gear and check the spline for wear as well as changing the seal. I say this because this same issue and my lack of understanding left us bobbing around for two days during a circumnavigation waiting for wind after loosing the gear due to a "slight shaft imperfection"
+++1 You can't run with any visible wobble, or a audibly noticeable wobble. nada, nil, zip, none. You should certainly check motor mounts but if it is the mounts your whole motor and tranny will be moving around as well. Not saying it may not be causing it though. You should check the mating of the propshaft flange to the tranny flange as well. It has to be to spec before anything else.
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Old 04-05-2016, 09:44   #11
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Re: Minor wobble of prop shaft

a lot of good suggestions. you shouldn't be able to see wobble with the naked eye. check the cutless or strut bearing first as that can be done in the water. you should not be able to "see" movement but you can feel it a little. we're talking .0002 inches and also the motor mounts as mentioned above. If all seems tight, disconnect the flange and check for trueness. haul out is next, to check the trueness of the shaft and look for uneven wear on the shaft at the bearing locations, this would indicate miss-alignment...ie...strut to shaft log to output shaft of reverse gear.

Left untreated that wobble could lead to new seals and bearing in the reverse gear. most of the previous will cost no more than your labor and a couple tools...that you should have anyway...the rest will be shelling out bucks. The longer you wait the more shelling.

check the prop too as an unbalanced ...ie...bent or chunks missing...prop can cast the afford mentioned problems. You would probably feel the vibration, from that tho.

good Luck
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Old 04-05-2016, 10:04   #12
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Re: Minor wobble of prop shaft

If you can see it, it's too much. No dial indicator needed. I'd check alignment first. What's the condition of the prop? possibly coated with barnacles?
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Old 04-05-2016, 10:13   #13
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Re: Minor wobble of prop shaft

If you can notice it, it is to much. I would give your cutless a serious looking at.
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Old 04-05-2016, 10:38   #14
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Re: Minor wobble of prop shaft

What isn't evident is what you were doing before getting ready to tighten the stuffing box nut?

I just went through the process of checking my shaft was straight by rolling it on the kitchen counter top. I was convinced it was bent. I replaced the engine mountings and it solved the issue. Running the engine without load and with high revs (out of gear) will not necessarily show you that the mountings are worn.

If this has continued for any length of time you should consider changing your cutlass bearing as a formality and consider the strut bearing as well.
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Old 04-05-2016, 13:05   #15
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Re: Minor wobble of prop shaft

A dial indicator and a magnetic mount to hold is an inexpensive tool. Search amazon.com. You will at least be able to quantify the amount of runout when you talk to the service tech. Youtube will overwhelm you with dial indicator vids. Look for Keith Fenner and/or mrpete222 to narrow things down.
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