Stripped splines on coupler

[dnhoogerwerf]

1996 Merc 7.4 Bravo 2. I removed the outdrive last spring to repair the shift cable. Re-installed outdrive. Used Merc spline grease, did not re-align engine. Everything went together great and ran the boat about 15 hours this summer. recently, while at low speed, prop quit turning. Removed outdrive to find coupling splines stripped out. Questions: What caused the splines to strip? Is this something that happens after time (500 hours on unit)? Should I have aligned motor when I replaced drive (it went together very easily)? Did the shift cable replacement have anything to do with this? It's a big job to replace the coupling (remove engine), so I would like to know what caused it to happen before I just replace the coupling. Anybody have any ideas?

 

[bruceb58]

Re: Stripped splines on coupler

Not aligning your engine was your downfall. I pull mine and check alignment yearly.

 

[ErieRon]

Re: Stripped splines on coupler

I recently spun my coupler splines after 24 years on a Merc 470 / Alpha One. In my case, the stringer that the front engine mount sits on began to sag and caused the misalignment. The (4) lag bolts were loose enough to pull out by hand. So, yes, misalignment is a definite cause and you should always check alignment before reinstalling a drive. I would thoroughly inspect your mounts and stringers as a precaution. Just my opinion.

 

[dnhoogerwerf]

Re: Stripped splines on coupler

Thanks for the inputs on mis-alignment. I thought if the drive shaft (from the outdrive) slipped into the coupler easily, the motor must be aligned or it would hit the coupler rather than slip right in.

 

[Bt Doctur]

Re: Stripped splines on coupler

That is somewhat correct if you were able to PUSH the drive on by hand., but if a front stringer or the rear mounts gave way, misalignment occurs silently.

 

[a70eliminator]

Re: Stripped splines on coupler

This maybe true when the drive went in, but who knows where alignment is now that you splines are gone, have you ever run it aground? Either way there's nothing else I could think of that would toast the coupler splines, but I'm an HVACR tech. not a boat mechanic.

 

[HT32BSX115]

Re: Stripped splines on coupler

1996 Merc 7.4 Bravo 2. I removed the outdrive last spring to repair the shift cable. Re-installed outdrive. Used Merc spline grease, did not re-align engine. Everything went together great and ran the boat about 15 hours this summer. recently, while at low speed, prop quit turning. Removed outdrive to find coupling splines stripped out. Questions: What caused the splines to strip? Is this something that happens after time (500 hours on unit)? Should I have aligned motor when I replaced drive (it went together very easily)? Did the shift cable replacement have anything to do with this? It's a big job to replace the coupling (remove engine), so I would like to know what caused it to happen before I just replace the coupling. Anybody have any ideas?

It's hard to say what for sure happened to your coupler.

My previous boat only went 39 years on the original coupler!!

I don't think the alignment was ever checked until I pulled the engine to replace it!!

For your's though, you NEED to inspect the engine mounting points very carefully and ensure that you adjust the alignment after you pull the engine and replace your coupler......Or you'll be doing it again soon...


I hope this puts to bed the idea that you can use a drive shaft yoke to check the alignment (like some have tried to suggest!!)




Regards,


Rick

 

[myoldboat2]

Re: Stripped splines on coupler

dnhoogerwerf, I lost two couplers in a few years. I used an alignment tool and got it about perfect, I thought. It turns out that the splines on the driveshaft from the sterndrive were too worn. When engaged in the new coupler splines, the shaft could be rotated just slightly. You can view the thread, with pictures, here. I ended up taking the upper bearing assembly apart in the sterndrive upper unit and installing a new u-joint assembly, which comes with both shafts.