I bought a 1972 Morgan 30/2 last year which had a hodge-podge of "improvements" which I have spent the entire year removing and replacing. The ONE thing he did right was to re-power with a BD1005 (love it, love it, love it!). I have finally been out a few times now and have realized that there is an issue somewhere within the re-powered system.
There is a rumbling from the gearbox (PRM 80), most noticeably -and sustained- at low RPM in forward gear, but also intermittently at all RPMs.
My max speed is ridiculous- about 3 knots.
I hypothesize that the previous owner did not change the prop from the A4 (1:1) when re-powering and that I am just grossly under-propped and once I have the correct prop the rumble will stop.
1) I am hauling out next month and replacing the prop- your recommendations would be appreciated.
2) Is the rumble prop size related, alignment related, or something else entirely?
3) Is it safe to use without damaging the PRM 80 (as best as you know)?
I suspect that you are correct in assuming that whoever repowered left the old A4 propeller on. The correct prop will make all the differance to the performance under power.
The figures that I have for the Morgan 302 are 27'6" waterline with a dry weight of 10,000 lbs. If these numbers are correct and you are limited to 12" prop diameter, then you will need a 12"x12" three blade propeller (Michigan Wheel DJ355 works well with my prop calc). This is definately a case where a smaller engine would give you a more efficient propeller and thus more boat speed. If you can fit a larger diameter prop you will get a great boost in efficiency. Let me know when you haul out and measure and we will work out the best prop for you. Your boat speed should be close to 7knots under power.
I suggest that you disconnect your shaft at the coupling and run the engine in gear to check if the rumble is from the transmission or from the shaft. If it is quiet with the shaft disconnected (I suspect that this is the case) then the rumble may come from a bad cutless bearing unless the alignment is way out. I would definately check the alignment before motoring further. If it is way out, it could damage the transmission.
Ran some prop calcs then had Krugger (here in Seattle) do the same- the only thing I don't really know with any certainty at this point is the clearance I have to work with. Of course I need it all done before the haul-out, but then it would be easy, right?
