Bertram31.com General Bulletin Board

odd markings on shaft

Posted By: joef
Date: Monday, 9 May 2005, at 4:25 p.m.

Men:

Putting the shaft zincs on this weekend. Noted some very strange marks on the port shaft, just at the point where it goes into the hull/shaft tube. I should have taken a picture as it would be easier to explain...1st the basics. The shaft is 1 1/2inch hooked to a cat 3208T 320hp engine on ZF225 gear (1.53:1 ratio). The prop is a nibral 22x24 threeblade. Last season, i did not notice any serious vibration - except a small rythmic thumping at WOT (i usually open everything up for a minute or so as i run down the flat, calm stretch to my dock.)

The marking was a "rub" mark on one side of the shaft only...it appears that the shaft had rubbed against the hull right where it enters the shaft tube. There was no real marks on the hull - it was hard to tell where it was hitting, and the shaft now appears to be sitting right in the middle of the tube (ie, its not htting anything now). I rotate the shaft by hand and it appears to turn true and is centered in the shaft tube. The cutlass bearing has no real visible unusual wear (no play in the bearing and the shaft seems cenetered with no wear indicating alignment problems) The cutlass was replaced last season.

I visually inspected the stringers, which are capped in 1/4inch steel and everything seems perfectly normal The engine mounts look OK - but i'm not sure a bad mount can be identified just by looking - still, none of them looked plainly broken.

I asked the marina to take a look at it - he didn't think the shaft was bent - suggesting that it would be either a motor mount, stringer problem, transmission bearing issue or...a shaft that would flex under heavy load.

...i've not ruled out anytying yet...but the "flexing shaft" theory would seem the best fit for these kind of markings. If there were stringer or motor mount problems, i'd imaging the whole engine would move and the shaft would get marked all the way around its circomference. If the transmission bearings where bad, i'd imagine seeing metal in the oil and other odd noises...oil leaks etc.

I plan to take a closer look at the motor mounts this weekend...the marina manager suggested using a crow-bar to test for movement in the mounts. ...other ideas are welcome.

...i don't know what these shafts are made of...they show some pitting (crevice corrosion?) around the stuffing boxes...so i'm deducing that, at a minimum, they are not aquament 22. If the motor mounts check out OK, and the engine alignement is close to OK i'm inclined to replace the shaft - as it seems the most likely culprit.

Anyone have this type of issue?

J

Messages In This Thread

odd markings on shaft
joef -- Monday, 9 May 2005, at 4:25 p.m.

Re: odd markings on shaft
Walter Kaprielian -- Monday, 9 May 2005, at 4:35 p.m.

Re: odd markings on shaft
Vic Roy -- Monday, 9 May 2005, at 5:09 p.m.

Re: odd markings on shaft
joef -- Monday, 9 May 2005, at 6:12 p.m.

Re: odd markings on shaft
Sean Burlingham -- Monday, 9 May 2005, at 11:05 p.m.

Re: odd markings on shaft
Carl -- Tuesday, 10 May 2005, at 8:52 a.m.

Re: odd markings on shaft
joef -- Tuesday, 10 May 2005, at 7:01 p.m.