Jcorstorphine
Well-Known Member
This is a follow-on from a previous posting where I raised the question about large clearance in new cutlass bearings.
http://www.ybw.com/forums/showthread.php?349336-Oversized-Cutless-bearing-problem&highlight=
In my case, a replacement bearing was supplied which still had about 12 thou clearance and was assured this was in line with tolerances. Boat was launched two weeks ago and I finally got round to starting the engine yesterday only to find a “moaning” sound coming from the bearing in both forward and reverse at tickover speed.
My engine has a tickover speed of 600 rpm with a 1.5:1 reduction so my shaft speed at tickover is 400 rpm. I have checked the shaft and it is free to rotate, I have also checked that the noise is not coming from my thrust bearing or flexible couplings. I can even hear the noise if I just flick the shaft round by hand.
If I run the engine at 1000 RPM the moaning disappears and does not come back until I shut the engine down and then restart it a day later.
In reverse, the moaning noise comes back after running at 1000 RPM but is less noticeable. I should say that I have not run the engine in reverse for as long as in forward.
Is this the new rubber bearing bedding in or is it the fact that it still has too much clearance? I do not recall having this problem when I last changed a cutlass bearing.
I should say that this is a bit of an oddball rubber cutlass bearing as it has a phenolic bush which is about 9 mm thick with the usual fluted rubber insert. The previous original Stuart bearing was an all rubber unit approx 12 mm wall thickness with no hard external bush.
http://www.ybw.com/forums/showthread.php?349336-Oversized-Cutless-bearing-problem&highlight=
In my case, a replacement bearing was supplied which still had about 12 thou clearance and was assured this was in line with tolerances. Boat was launched two weeks ago and I finally got round to starting the engine yesterday only to find a “moaning” sound coming from the bearing in both forward and reverse at tickover speed.
My engine has a tickover speed of 600 rpm with a 1.5:1 reduction so my shaft speed at tickover is 400 rpm. I have checked the shaft and it is free to rotate, I have also checked that the noise is not coming from my thrust bearing or flexible couplings. I can even hear the noise if I just flick the shaft round by hand.
If I run the engine at 1000 RPM the moaning disappears and does not come back until I shut the engine down and then restart it a day later.
In reverse, the moaning noise comes back after running at 1000 RPM but is less noticeable. I should say that I have not run the engine in reverse for as long as in forward.
Is this the new rubber bearing bedding in or is it the fact that it still has too much clearance? I do not recall having this problem when I last changed a cutlass bearing.
I should say that this is a bit of an oddball rubber cutlass bearing as it has a phenolic bush which is about 9 mm thick with the usual fluted rubber insert. The previous original Stuart bearing was an all rubber unit approx 12 mm wall thickness with no hard external bush.