Vibrations
Dear J. Mansfield Thank you for your letter. My first thought would be that the transmission is slipping. The inconsistent pattern of slip can and could be caused by adverse loads taking place at the time the vibration starts. Have you looked at the transmission oil? Is it discolored? If discolored it could be burnt which could be caused by slip. Take a look at the linkage on the transmission to make sure that there is complete engagement. When out of adjustment adverse loads or spikes in load could cause the transmission to slip. The reduction or cycling down of the Rpm’s reduces load and allows the transmission to again engage.?. My second thought is that the propeller is going through a cavitation cycle, which will cause mass vibrations at sporadic ranges of Rpm’s. Lowering Rpm’s allows water to fill in and around the prop allowing it to drive again. This could be caused by excessive sporadic loads and too much pitch for the given propeller tip speed. This could possibly be confirmed by running the engine, while transmission is in gear, to it’s maximum throttle and checking to see that the max rated Rpm’s are achievable. As for the PSS there should be no connection between the problem and seal. The seal is load free to the running gear and would not have any impact to the transmission or propellers ability of functioning. As for the running gear, the only components, which have capability of slipping, is the transmission and propeller. This is of coarse hoping that you are not having a complete failure of some other component structure, which then should be, constant and not just sporadic. Hope this helps. Kevin L. Woody
