Engine coupler & gear ratio question

[ErieRon]

1984 Mercruiser 470R (S.N. 6701134)
Alpha One, counter rotating drive (S.N. OA706258)
19 pitch, 14.5 Dia. prop.
3800-4200 WOT

I have a 23' cuddy with a Mercruiser 470R & an Alpha One (new in 2002), counter rotating drive. I suspect that I have spun the splines on the engine coupler. In neutral, on muffs, the coupler shaft does not turn at all & no gear engagement. Drive seems OK as it shifts and locks into forward & reverse as it should...but the prop won't turn.

Question: Is there a rubber component to the engine coupler, or just the prop hub? I've read numerous threads and I am still not certain.

Further, this is my 3rd drive (2 stolen), and Don S. informed me that I now have the wrong gear ratio for my engine. Original ratio was 1.84:1, and the current drive is a 1.62:1 (S.N. OA706258).

Question: What, if any, are the ramifications to this difference & do I need to change it back to original, or at least closer?

Thank you in advance.

Ron

 

[bigskiohio]

Re: Engine coupler & gear ratio question

I would think you would be able to just change you prop and you would be okay. Your coupler will be similar to this .

 

[Don S]

Re: Engine coupler & gear ratio question

Question: Is there a rubber component to the engine coupler, or just the prop hub? I've read numerous threads and I am still not certain.

The coupler is part metal and part rubber, but your problem is not the rubber part. You have the metal splines stripped out of the coupler. The rubber part would have turned the upper in neutral to turn the pump because there is very little resistance. But with the load on the prop trying to get on plane it would slip from the load and you would smell burned rubber.

With the wrong gear ratio, you are going to loose effeciency, both in top speed and the ability to get on plane.

 

[ErieRon]

Re: Engine coupler & gear ratio question

Thanks again Don...for clarifying. When it went, it happened from a stand-still while I was going to set up a new drift. It just spun as soon as I put it in gear. I never smelled any rubber burning or anything else. Today, while I was running it on muffs to see if the coupler shaft was turning, it wasn't pumping any water.

 

[Bt Doctur]

Re: Engine coupler & gear ratio question

The most likely cause for coupler failure is rear motor mount bushings went bad knocking engine /coupler alignment off.

 

[ErieRon]

Re: Engine coupler & gear ratio question

The most likely cause for coupler failure is rear motor mount bushings went bad knocking engine /coupler alignment off.

Thanks for that advice, I appreciate it. One more thing to add to the list of things to do while the engines out.