Strut Alignment

[P69]

Among the chores of this fall's haul out was to replace/seal off the remaining original thru hulls and replace the shaft and cutless bearing.  When I aligned the new prop shaft in the boat, I saw that it would not align perfectly with the cutless bearing (new shaft, new cutless bearing).  It was so bad that the shaft was hard to turn by hand.  I saw this a few years ago on haul out and the cutless bearing rubber had worn unevenly to compensate for the misalignment. Of course, there was no problem turning the shaft by hand with the worn cutless bearing. Back then I thought it was just bad v drive alignment and ignored it until I got round to properly fastening the v drive to the hull (ended up removing the old wood-based v drive beds and made some new ones out of fiberglass). Now that V drive is aligned and, with the shaft completely loose and unattached inside the boat, it still would not align even when sitting on the bottom of the shaft log. The inboard end of the shaft was too high. I decided to remove the strut and rebed it with thick epoxy to get it closer to perfect.

I thought it might be hull flex from being out of the water, but quickly discarded that because last haulout I saw no visible hull flex; the shaft rotated as smoothly with the boat out of the water as did in the water. Additionally, once aligned, there was no noticeable difference with rotating the prop on land or in water during this haul out. Tonight, when I put the boat back in  the water there was no noticeable difference in alignment. I realigned in water, but it was off just by about 0.002" - 0.005". i got that straightened out to within +/- 0.0015". I'll recheck  tomorrow when I go get the boat. There is undoubtedly some flex, but this strut alignment  issue is not flex.

I ended up digging out the strut pocket, removing the strut, adding some thick epoxy to form a shim that now holds the strut parallel to the propeller shaft.

Like all other fittings, Pearson used silicone on the stut.

As far as I can tell, the problem originated at the factory with sloppy install of the strut. I don't think a PO lifted boat with sling on the prop or strut because there were no stress cracks or crushed fiberglass on the after or fwd ends of the cavity. Another possibility is an imperfect strut. Either way, it's fixed now, with about 1/4" of epoxy at the after end to bring it into parallel alignment with the shaft.

I removed strut, put it back in place with a 'pad' of thick epoxy and adjusted the mounting bolts to make strut parallel to shaft.  Only problem I had was that the holes drilled by Pearson during original install were not straight, so when I tightened the bolts, the countersunk heads slightly skewed the strut alignment athwartship, causing slight contact between shaft and cutless bearing rubber at 9 o'clock position on both fore and aft ends of bearing. It barely contacts, but I was disappointed that it was not as perfect as the dry fit. The only way to solve this would have been to fill the existing holes with epoxy and drill new ones. This offset amount was not worth the extra week in the yard waiting for two more epoxy cure cycles (3 days)

I had to move the engine forward about a foot  to get access to the strut bolts. They were double-nutted and there was no way I could get the leverage under the engine to break the pair of nuts free. Once the double-nuts were free, the main nuts spun off easily.

1.  Removed the strut and cleaned the molded-in cavity
2.  Aligned the shaft with the v drive, using a V-jackstand holding the shaft in place (strut was hangin loose)
3.  Dry fit the strut to unmodified cavity to ascertain the degree of rotation needed to make strut bearing parallel to shaft (eyeballed cutless/shaft alignment so there was equal gap all round shaft in bearing).
4.  Wrapped strut in plastic to prevent sticking to epoxy, spread a thick layer of thickened epoxy to the mating surface of the strut,  and bolted it back to the cavity, while eye-balling the strut/propeller alignment.
5.  Adjusted the four strut bolts to bring the strut in alignment with the shaft. Let epoxy cure over night
6.  Remove plastic/tape and grind off all epoxy that will not be covered by strut contact surface.
7.  Dry-fit with new bronze bolts and recheck alignment
8.  Gooped up with Sikaflex 291 and bolted in place.
9.  Clean all caulking and let it cure
10. Backfilled the cavity with thickened polyester resin
11. Laid in two layers of 1708 over the filled-in strut cavity with polyester resin
12. Ground/sanded smooth, then painted: Done!!

I used thickened polyester because I want to be able to relatively easily remove that filler in the future and epoxy is not easy to chisel out or separate form the cavity walls

Attached are a few pictures. Follow this link to look at all of them.
http://bodylens.com/Gallery/thumbnails.php?album=32

[SVJourney]

Nice work!

As far as I can tell, you are the only one to post up a repair like this.  Thanks for the info and great write up.
Wayne

[Capn]

I also had this done on my 367.  When we found that the shift was out of true in 3 places, the yard determined that the strut did not allow alignment with the v drive. They removed and re bedded the strut to solve the problem.

[Dale Tanski]

Did you notice any reduction in vibration after the repair?
Thanks...
Dale

[PeteW]

When you said " it still would not align even when sitting on the bottom of the shaft log" I am assuming that you are saying that if a straight line (you can use a string) down the center bore of the strut, and parallel to it, does not go through the center of the shaft log diameter then the strut is in misalignment to the shaft log.  If that's what was going on I agree that your problem was strut alignment.

Strut misalignment can be seen with the naked eye by looking at the cutless bearing with the shaft installed. If the bearing rubber is pinched on one side and loose on the other you have a lot of strut  misalignment. Or you can measure the clearance around the bearing in 4 places forward and aft and use a little trigonometry to determine the misalignment in degrees.

So armed with that data, how much cutless bearing misalignment is tolerable? I've been to every manufacturers web site and all I can find out is that misalignment of the cutless bearing is bad and it will cause wear, create vibration and hurt your efficiency. But I can't seem to find an answer as to how much is acceptable.

Winging it I figure that if I consider the clearance of .015" for the water film in the bearing on a 3.5" bearing you get 0.24 degrees of slop max.  At the end of a 60" shaft that means you have about plus and minus 1/4" to get the V drive into the correct location. That said I know the rubber bearing is considerably more pliable so it may be very easy to get yourself into a bad situation in terms of alignment.

I suspect that over time a mildly misaligned cutless bearing will wear in, if its rubbing on one side or the other. Once it can support a water film without friction is stops wearing and remains like that for most of its life. But excessive misalignment which blocks water from flushing dirt out of the grooves in the bearing will allow dirt to score the metal shaft. Once the shaft is scored the bearing is toast.

Thanks for the post(s). This is probably a bigger problem than most of us realize.

Pete

[P69]

Pete, Yes to your first paragraph, that is exactly what I saw, but I just used the shaft instead of a string; it was so obvious.

I like the string idea.  If I had used that, I would have ascertained how much out of alighment it was, but don't know if I could have done anything with that info.  The method I came up with seemed to work, using the shaft with the strut loose/supported and aligning the v drive.

When I removed the stuffing box and just let the shaft drop to the bottom of the shaft log, the inboard end of the shaft still needed to go down farther, but I figured rebedding the strut was easier than moving the shaft log.

In that loose state, the shaft pinched the rubber in the fwd end of cutless bearing on the top part of the arc (pinched top, all gap on bottom) and pinched the rubber on the bottom of the arc on the after end (pinched bottom, all gap on top.

The pinch was so tight that it was difficult to rotate the shaft by hand, unless I used all my strength; I had to fix that.

I do remember that the previous cutless bearing had more than half of its rubber thickness worn away (fwd: top, aft: bottom worn) to accommodate the skewed strut.

With strut rebedded, there is an very slight gap difference between the shaft and the cutless rubber through its circumference. I had no observable  difference in the gap between shaft and rubber (I didn't bother with feeler gauges), but when I tightened the strut bolts, a slight gap difference formed in the vertical dimension.

Dale, I did not notice any difference in vibration levels. I removed the engine in January of 2016 and don't really remember enough to accurately compare pre/post vibration levels.  I also replaced the damper plate, which made a lot of noise, now it doesn't. It's possible that 1) there was no atypical vibration or 2) there is no decrease pre/post.  I also have a new prop (campbell sailer, we'll see how that goes). The old prop (2 blade michigan wheel) had some small dings on its leading edges, might have been out-of-balance.

Now, all the below-the-waterline work is done and I can focus on the interior.