when you pull the drive, take a flash light and look at the coupler splines, they should not have sharp edges on the splines, they should look like the ones on the input shaft, If they come to a sharp point, change the coupler NOW or it will leave you in a bad place. If you purchase a tool, it should glide in with little effort and turn the same, use a good high pressure spline grease when you go back together. Good Luck

Yup! Couldn't agree more.

OK guys. I got my alignment tool and pulled my outdrive. The alignment tool went right in and turned fairly easy. Not with 2 fingers or anything but if I wrapped my whole hand around the knurled end i could definatly turn it without much effort. I looked at the splines and they are perfect, not sharp or worn at all. I bumped the engine and it seemed to line up about the same, then I pulled my coil wire and had a buddy crank on the engine with the alignment tool still installed, and it did wobble a little. I had the marinas mechanic look while I cranked it too, and he wasn't too worried about the wobble?? The owner of the marina said maybe the coupler/flywheel bolts were loose? Not sure about that without pulling the motor, but I do know that the gimble bearing felt perfect, the u-joints look and feel perfect, the upper gears in the outdrive look like new with the hint of a wear pattern starting very uniformly on the gears, and the gear oil was right at the top plug where it should be. I put the outdrive back on and drove it all weekend. I ran it several times wide open and it actually seems to smooth out at higher RPMs, but under a load especially with a full boat load of people and the trim all the way down, it definately has a vibration. Maybe I'm just paranoid, and I think it has gotten a bit quieter as the drive has broken in, but I'm telling you, there is something not quite right! I should try to see if the Marina will lend me an entire outdrive to see if it is the drive or not. Doubt they will though..........

Any wobble in that coupler is bad news. My moneys still on that being the culprit.

I've been thinking though, and maybe everybody's over-thinking this, including me. Have you tried a simple prop swap? Maybe you've got a bad prop.

prop swap----exactly----process of elimination from simple to more involved----good point. takes only a few minutes and you will know right away if it feels better----it also seems the age of the coupler was never told----you mentioned that the engine was swapped a few years ago but same coupler used----which would be no problem as long as it was in good shape and not getting dry-rotted or fatigued-----i just blew my coupler last saturday and although i have oinly owned the boat a very short time i bought it from the original owner who was very meticulous about keeping up with this checkmate----however, and im not sure, the way mine blew instantly when i snagged on something led me to believe it was either original (22 yrs old)---or at least old and fatigued----either way a new one from mercruiser is on the way and i hope to be putting it in on thursday---i recommend doing the same and buying an OEM coupler as ive gotten feedback that aftermarket ones may not be as sturdy-----good luck with it.

a prop swap is a good idea, but there should be no woble it the coupler, any woble there goes right to the gimble and then to the u-joints, and will cause your vibration, when you cranked the engine over with the bar in place, it should have been straight as an arrow, my guess is coupler.

I have tried the prop swap yes, not the problem. I sure thought that wobble looked bad as well. I know the coupler is mostly rubber so I thought maybe (especially after the marina mechanic blew that off) that was acceptable. As far as the age of the coupler, the boat is an 84 and I have no reason to think it has ever been replaced. I did replace the motor 2 years ago, but I put the original coupler back on. Not sure why this vibration just started this year with the new outdrive, but blowing the old outdrive the way I did certainly could have driven the coupler over the edge. Hell, it only takes an hour to pull the motor on this thing once I find a picker........last time my bro-in-law who flies our local copper chopper, let me pull into the police hangar and use the electric chain hoist they use for pulling chopper rotors and blades which worked great, but he was a little paranoid about his superiors catching on so i'm a little hesitant to ask him again. If I get the drive pulled and unbolt the motor mounts, wire harness, and transom water hose, i could be in and out of there in an hour easy...... what the hell, I'll ask him. Thanks guys!

I had a freind who bought a new SEI drive, and he said it growled for the first twenty hours or so, then it was fine after that. I believe these are actually built overseas, and I'm sure the tolerances aren't as good as Merc's. I haven't heard of one blowing though. I guess they just have to break in.

my buddy jeff and i did my coupler job on thursday in only a couple of hours as well---not a bad job at all---i was able to get a brand new mercruiser coupler out of nj on ebay for 209 bucks plus shipping-----i thought that was a pretty good deal---and it was here in a few days-----hoping to put it out on the water today and run the boat----lets hope no vibrations or other problems. let us know how you make out once that engine coupler is replaced in your boat k???