I just had a wasted exercise pulling an SD20 apart to investigate just such a noise
The noise could be heard in the cockpit
, but not audible when poking my head
in the engine hatch
. I had a weeping oil leak
from the front seal. With a bit of hard running it must have leaked a bit faster due to getting hot and it was down about 250ml. I suspected I had killed the saildrive
due to a bearing running dry.
So with the boat hauled out I had the Yanmar
specialists remove and strip it apart. They found nothing wrong! So back in it goes, and this time I had a closer look at the prop and compare to the other side (if only I had done so before
The prop on the noisy side showed a slight evidence of contact wear on the outer edge, hardly a mm deep. Fitted to the saildrive
there was plenty of clearance, so it must have only moved forwards under load.
So I took it to a prop specialist at Southport and he declared it looked fine. Nevertheless, I decided to get it rebushed which he did within a couple of hours. He also offset the bush slightly to give even more clearance. The removed bush looked perfect. He did say that the original Volvo
bush is softer than what he replaced it with.
So, the boat is now back in the water, with me wiser and poorer and no good explanation of what was really wrong. At least the noise is gone and the weeping seal replaced.