Re: 87 ski centurion
very few tournament inboard owners on this site. you'll get better answers at wakeworld, wakeboarder or there may even be a centurion owner's site. i've got an 87 inboard too...supra.
usually, the shaft and coupler are sold together as a matched set. i've had to cut a shaft to remove it, not a fun time. the shaft can get lodged in the coupler really tight. but, you should be able to get the coupler off the transmission. if not...ouch. that's a big problem. if you can get the coupler off, you might just need to align the engine. the engine mounts allow you to move each corner independently so that things line up. with the coupler separated from the transmission, the coupler and transmission plate should line up within .002 tolerance on all sides...going from memory on that number.
it's also possible that the strut underneath the boat is out of alignment or bent. inside that strut are rubber bushings. you should be able to see the end toward the prop. can you tell if the rubber is worn evenly? they do wear out so if you end up pulling the shaft, might as well replace those. with the right tools, i've heard you don't need to pull the shaft to access them.
there's a really good prop shop where i live (nettles). i've always brought my old shaft in when ordering a new one. they don't want to accept the risk of ordering something wrong so they will ask what size you need. centurion is still in business so you may find an answer by contacting them. or, you might find some fellow owners on the sites i mentioned.
getting the coupler off the transmission is a must though. i'd concentrate on that first. then i'd check alignment and the strut and hope your parts are good.
don't run it with a bad vibration, you could mess up the transmission...or break the shaft and possibly take on water. either way, lots more damage could result.
