F32 Prop Shaft Alignment

DK · Post by DK » Wed Sep 14, 2011 9:52 pm

I am in the process of replacing the inboard stringers on my F32. I noticed the starboard prop shaft is not centered in the stuffing box flange and is touching the bottom of the brass flange looking from outside. the port shaft is also not centered but not touching.

with both engines and transmissions disconnected and removed from the boat, it is my assumption that the shaft should be centered in both flanges. What could be causing this misalignment and what is the suggested corrective action necessary to properly align the shafts?

captainmaniac · Post by **captainmaniac** » Wed Sep 14, 2011 10:56 pm

Alignment really means that the shaft coupling coming out of the transmission and the shaft from there back are aligned, and that means the engine isn't 'twisted' side to side, or 'tilted' forward or backward compared to the shaft.

To resolve what you have going on really requires one of two things, depending on that the root cause is... One possibility is that the engine needs to be shifted in position - in your case, raised a bit to lift the forward end of the shaft enough to clear the flange. After raising the engine, an alignment would be performed again to make sure that everything lines up right (just with the engine sitting a half inch or so higher).

The second possible problem you could have is with the strut. If your strut is bent out of shape, or loose, it might not be holding the aft end of the shaft in the right position. I had the backing plate (wooden block) start to get soft on one of mine a couple of years back, letting the strut move around a bit. Had the block replaced (ugly job as it's under the fuel tank) and all is well now.

If the strut seems solid, your problem is probably that the engine has settled a bit.

captainmaniac · Post by **captainmaniac** » Wed Sep 14, 2011 11:02 pm

Oh yeah - re the second part of your question... not necessarily. With things disconnected, the aft end of the shaft will be supported by the strut, the front end will be supported by your stuffing box or shaft log. The stuffing box / shaft log is a flexible coupling that can move around a bit, so any flex in it will dictate how centered the shaft is compared to the flange. Once hooked up to the transmission, the shaft will 'pull' the shaft log and stuffing box up/down/left/right as necessary, so essentially it follows the shaft where it moves.

Similarly, if you have some vibration or wobble in the shaft the shaft log / stuffing box will move with the wobble, and maintain the seal.

vabeach1234 · Post by **vabeach1234** » Thu Sep 15, 2011 7:33 am

If the boat is out of the water and on blocks or stands, the hull may be flexing and not in it's natural, in the water state. I know that when I block my boat, the propeller binds a little on the strut bearing and is difficult to turn by hand. When in the water, the propeller turns very easily by hand.

jav · Post by **jav** » Thu Sep 15, 2011 8:30 am

what your seeing is normal with the engine room end of the shaft not connected. The shaft is heavy and will naturally sag (gravity) making it "look" like it's not centered.

DK · Post by DK » Thu Sep 15, 2011 9:43 am

Thanks for the guidance. My struts were removed, bushings replaced and re-beded about 9 years ago. I checked them and the bedding and they seem OK. Once I complete the stringer replacement and re-install the engines and transmissions. What is the suggested alignment process?

Since the boat is on land, can I temporarily shim the shaft with wood shims so that it centers in the sutffing box flange and then align the transmission flange to the shaft coupling flange? The alignment would be re-checked with a feeler guage once the boat is launced and sat in the water a few days.

jav · Post by **jav** » Thu Sep 15, 2011 11:27 am

You can ( block them) but it's not necessary. As far as aligment goes- it depends on how thorough you want to be. If you trust that the shafts are straight, your struts are aligned with the shaft logs and that your cutlass bearings are good- you can do rough aligment using the power plants and visually center the shaft in the log.

Once the boat is floated, and the hull is given a few days to settle back to it's natural floating shape, then do feeler gauge aligment at the flanges being sure that you move the engine and gear and not the shafts location in the log. Remember- the goal is to move the engine and tranny into aligment with the shafts location- not the other way around.

Big D · Post by **Big D** » Thu Sep 15, 2011 10:09 pm

Support the shaft so it sits in the middle of the tube (on the outside) then check to see how it is sitting in the strut bearing. The shaft should not be crushing the bearing on any side. Bear in mind that there is some leeway here; the shaft doesn't need to be exactly in the middle of the tube. If you can't get it in an acceptable position, you'll need to find why it's out; bent strut, strut alignment change etc. Once shaft is in the correct spot, keep it supported there while you install the engine again. Do a rough engine alignment to the shaft's position. Final alignment done after a day or two in the water. No more than .003 out. Check at 12, 3, 6, 9 oclock. Rotate coupler 180 deg and check again. If the reading changes, your coupler is warped. Then rotate tranny flange 180 deg and check again. If your reading changes this time, your flange is warped. Take your time to do it right the first time so you won't have to uncouple the coupler, untighten the engine mounts and start all over again.

By the way, before putting it all back together, now's the time to repack the shaft logs. When the shafts are aligned, ensure the packing nut is not rubbing on the shaft. If the shaft is centered and the nut is rubbing, sometimes it's just a matter of loosening the log tube and repositioning it.