1987 268 sundancer engine coupler

[Samuel Thomas]

Hello!
Recently purchased a 1987 sundancer 268 with a 260 5.7l
Came with a 21pitch prop and tried a 17 still not really getting over 24mph so I tried a 15x15 and it's great 34mph! But after 3 hrs or so original engine coupler failed.
It was replaced, aligned and about 8 hrs later it failed again. I am trying to figure out what happened, engine mounts haven't moved and are I very good condition. The lower was apparently just serviced. Brand new shaft and grease.
Is it possible to get a bad coupler? It was quicksilver brand and the box was very old.

 

[techmitch]

Recheck alignment, check integrity of engine mounts both fore and aft, check stringers and transom for rot.

 

[Samuel Thomas]

I will check again once new coupler is installed, but I am asking if not alignment or mounts what could it be?

 

[scoflaw]

That's about it and lack of grease. Did you do the alignment yourself or take someone's word for it ?

 

[Samuel Thomas]

Did it myself with local marine tech, used splined alignment bar. Also when pulling the drive back off tons of grease and no damage to either splines

 

[scoflaw]

So it broke loose at the rubber/steel bond ?

 

[Samuel Thomas]

Yes correct, the rubber seemed to have ripped off the main hub that bolts to the flywheel

 

[scoflaw]

Could be defective. Never heard of a splined alignment bar. How would you get the alignment right with that ? there would be no witness marks to look at.

 

[Samuel Thomas]

Only the tip is splined for a tight fit in the coupler

 

[scoflaw]

So how do you tell how tight is too tight and which way to move the adjustment if it needs moving.

My suggestion would be to get a regular bar with the smooth end.

Check out some Youtubes on the subject

 

[Samuel Thomas]

I can try that for the next one, this was basically the yoke with a extra 2 foot

 

[Samuel Thomas]

So small update, this time had a new coupler installed by a local mercruiser mechanic. Had him check alignment before attempting to adjust to see if I did it correct. It was perfect, or very close. He ended up adjusting the nits on engine mounts a 1/4 turn each to get it perfect. He does not believe alignment could of been the culprit being so close and no wear at all on the yoke splines or the coupler splines.
So I said what the heck check the drive maybe it is seizing up the fluid came out looking brand new, no metallic shine at all, he actually asked if I just changed it. But I had it refilled thinking it should be fine.
Then had the same mechanic that did it with me the first time (very close friend) go check it and it was exactly the same with either alignment bar. Then the only other possiblity is bad mounts or rot so had them check transom and stringers for rot and they didnt find any. Mounts are very solid and not rusty at all.
So final test was lube it up and start it to see if the flywheel was true. It was perfect no wobble or vibration.
I assume I must of gotten a defective unit, everything checks out 3 times over with 3 different people doing it. Kinda at a loss if it goes again and I am slightly worried about being stranded again.
I fell in love with the sea ray sundancer and all the wood in the cockpit and cabin I would hate to move on from this boat.
Side question do they not make stronger couplers? What do the big 454 and other motors use? Because if I am breaking them with 260hp on a good day then I am not sure what direction to go.
Thanks for the responses so far!