Another Hard Knock Story

[capejt]

While reading though the post of Morgantheship, regarding his hard knocking problem in his drive line, I was overcome with deja vu. I have a similar sound coming from the drive train of my 1979 H33 (Yanmar 2QM15). I've managed to isolate it behind the the tranny, possibly the shaft log tube. It acts up at higher RPMs and only in forward gear.
Now, here's where I start scratching my head. I've experienced this noise since I had the yard replace my cutlass bearing, and I replaced the Shaft log with a PSS. Nobody touched anything as far as the engine alignment is concerned. I could understand if the shaft were out of alignment a little bit. In fact, as I recall checking the shaft as it comes out of the hull, it IS off-center a bit.
From everything I've been reading it seems to me that I need an engine re-alignment, but what I'm wondering is could something be done to correct the shaft if IT is out of whack (alignment-wise)? The only things I can come up wih are...
1. When re-attaching the prop shaft flange to the prop shaft, maybe it went on slightly askew?
2. When re-attaching the prop shaft flange to the tranny flange, perhaps I didn't line up hole "A" with the other hole "A", but rather hole "A" with hole "B" or "C" on the flange.
3. Maybe (by timing coincidence) the engine mounts have gone bad and are in need of replacement. The engine DOES shake a bit.

Also of note is the fact that the boat is in the water so it kind of limits my flexibilty in correcting things.

I'd love to hear what you all are thinking about this one.​

 

[Ken13559]

I once had ocassional knocking noise from prop shaft. When it happens, its usually when driving forward. I have to run abit of reverse and forward to quit the noise. Later on haul out, I notice the prop nuts could be turned by finger strength! Its probably the nuts unscrewed during driving and the prop got pushed backwards by water movement and came loose creating the knocking noise. A little reverse and forward put the prop back. So after I tighten the nuts at haul out, I've no more of such noise.

 

[Don12364]

Possibly due to the PSS

I had an identical experience after fitting a PSS stern gland.
The original gland with its packing had the effect of stabilising the propshaft via the rubber tube on the log tube coming out of the hull.
The PSS has no packing so does not tend to act as a journal (i.e. a bearing) on the shaft. Any tendency to 'whirl' was damped out but not so with the PSS.

I too checked the shaft alignment and it needed a small movement of the engine to centre it - and of course a slight change of angle to get the flanges parallel again.
Then all was okay.

You might like to try having someone else helm the boat and alter the power levels whilst you watch the PSS to see if it begins to vibrate.