I have a 91 Yamaha 200 on a 21 Cape Horn that I have concern about and need your knowledge and experience for if you're willing to help. <br /><br />I bought the rig used. The cavitation plate was cracked so I removed the Lower Unit (LU) and took it to a prop shop where they welded it for me. When I got the LU back I put it on the boat and checked the oil in the gear case finding it empty. I ASSUMED that the welder had drained it so I refilled it and took the boat to the Tennessee River here in Scottsboro, AL for a test run. First time in the water. (I know..crazy to buy one without testing but I got a hell of a deal on ebay.) <br /><br />When I launched I noted that when in gear at idle there was a heck of a racket and vibration in the motor. Even the slightest increase off idle silenced the noise and smoothed out the vibration. Ran perfect at speed. The prop is in like new condition. <br /><br />When I got the rig home I again checked the gear oil finding it contaminated with water. Pressure testing revealed that the unit needed resealed. <br /><br />I had the unit resealed and changed the bearing carrier at the same time. The mechanic said he inspected the gears and they looked fine. <br /><br />But the condition noise and vibration was still there. I noted that the shifter was not fully rotating to the fully advanced position in forward gear position at idle but did advance to full rotation when the throttle was opened slightly. This I attributed to 1. a clearly worn bushing on the linkage, and 2. Probable stretch in the shift cable and a corroded and stiff control box. I replaced the bushing and the gear box with a like new one I purchased from a member on this site and adjusted out the cable slack to enable full travel into forward gear at idle. This corrected the "short" travel of the shifter rod. BUT THE NOISE/VIBRATION REMAINS. <br /><br />Now it's time for further troubleshooting. The (really very experienced) mechanic who resealed the LU for me said that he has experienced this with other 200 Yamaha engines with stainless props and that he feels it is perhaps caused by excessive gear backlash condition. Says they don't seem to do it with Alum props. <br /><br />Well I don't know if I believe that, but I'm trying to determine how much fore and aft movement on the prop shaft is acceptable. I feel that mine perhaps has too much and that that may be the cause of the problem. I suppose if the gear teeth aren't damaged the gear backlash might be able to be shimmed for adjustment. I really don't know. <br /><br />What's your take on what is acceptable amount of movement. I can measure mine with a dial caliper to get the exact amount there but I'd guess it more than 1/16" but less than 1/4" by good measure. It certainly is more than on a 115 Yamaha, old 115 Merc, and an old Evinrude 85 that I own. <br /><br />Got any feel for this? <br /><br />Steve
