Shaft Wobble

[Marshall Mahoney]

Define shaft wobble -- how much is too much? I have always had some shaft wobble with my old 453's and my new(er) Cummins. Should there be no visible movement with the packing gland to the point where I could balance an egg on it?

[Stephan]

I can't answer what should be but can explain my experience.
I have the traditional bronze shaft logs and flax packing. The hose connecting the shaft log to the packing fitting allows some movement. For the first three seasons I ran the boat there was a "tremble" of the packing fitting. It was clearly not perfect but it worked.
Then the tremble turned into a shake on the starboard shaft and I saw some weeping around the shaft log. With the Brother's help and encouragement I can report that things are back to a tremble. The shaft straightening process is here http://bertram31.com/newbb/viewtopic.php?f=2&t=8652
Hope this helps-
S

[Marshall Mahoney]

Thanks Stephan,
Machine shop says my shafts are good. I need to bum a ride off of one of the 31's in the marina for comparison...

[Carl]

Shaft wobble is an open term...does not define much as one person may think it is excessive...another says its fine.


Ideally you want shafts running dead true, no run out.

That said its an uphill battle to achieve that across the rpm spectrum...under loads that wobble can creep in. As boat pops on plane the wobble stops or is greatly reduced. Could be load moves engine a bit on it's mounts screwing with alignment, could be a blade on prop flexing a bit, could be shaft out and load makes worse...could be as rpm increase or changes the shaft finds its center and calms down...could be water supporting shaft at speed...whatever the case, some rpms will give more wobble or runout.

To reduce:
- shafts need to be straight.
A relative term as length, support of shaft (intermediate strut, log) and rpm make a difference. Our size shafts .005 is about the max runout you should see. My boat when it had 1:1, direct drive with 440's... anything over .003 shook the boat. A wheel done by most shops, shook the boat. When I went to 1-1/2 :1 the shaft shortened several inches with reduction gear and shaft spun alot slower....so I was able to get away with more runout and got away with using a friends shop to do my wheels.

Coupler should run dead true to shaft

Tranny coupler needs to be running dead true...my last boat that coupler was bent.

Cutless need to be in good shape...little to no play and running concentric with shaft...not pinching rubber bearing

Shaft overhang beyond strut should be no more then 1-1/2 times the diameter.

Your wheels need to be right on, balanced, checked for tracking, pitch etc. A weak blade can also flex under load...so a happy go lucky prop adjuster with a heavy hand on the grinder can wreak havoc on your wheels.

Motor mounts in good shape...can't have motor flapping around.

Get all those right on and that wobble should be negligible, reduced to "abit" under load...or dead on.

[Marshall Mahoney]

Thanks Carl -- mine is more that negligible. Didn't think about the gearbox coupling. Looks like they are "only" $400 on line...

[John F.]

The wobble in the port shaft on crows nest was caused by a worn coupler that the shaft guy couldn't get to stay true on the shaft. I think the new cousr was about $150.

[Carl]

Thanks Carl -- mine is more that negligible. Didn't think about the gearbox coupling. Looks like they are "only" $400 on line...

As they say, nothing is cheap anymore...except me.

Tranny coupler usually is fine till somebody cranks on it when its used as a makeshift shaft puller. You know when you spread the couplers, place a socket in between shaft, grab some longer bolts then tighten the couplers together pushing the shaft out of coupling. Some don't use a small enough socket or they don't center as they should, some shafts are really tight, others crank the adjacent bolts...whatever the case...I have seen some bent tranny couplers. Toss in lathe, indicate, true up the face and your back in business. Buying new...$$$ when available.

[Marshall Mahoney]

Thanks guys. I fiddled with a dial indicator all day Friday. I'm leaning toward bent shafts. Will pull them later this summer...