Mercruiser Alpha I Gen I upper ratio?

[SCORPIO]

I've got twin Merc Alpha I Gen I sterndrives on my 89 300DA with 5.7 V-8 engines. What ratio do the 5.7's use, 1.5:1?
I'm doing bellows and shift cables and I noted that my starboard drive, the one with the shifting issues, has a large amount of salt and corrosion around the shift shaft and in the bell housing. The shift shaft was almost frozen from the corrosion, I had to use a pry bar to get it all the way in to forward to get the drive off, hence the shifting issue. Looks like the upper housing is warped and not anywhere near flat on the small, skinny little bit of metal that separates the ocean from the inside. The upper also has some corrosion and issues with threads on the oil vent plug so I'm thinking of just getting a new SEI upper and putting it on. I have a good used bell housing (hood) that I'm going to swap in while doing the bellows. I just need to know what ratio to use with 5.7's. My ID tags are long gone from the drives.
Thanks

 

[boatman37]

As far as I know mine is 1.50. I have all the factory documentation for mine and thats what it says. Can't say for sure a bigger boat with twins would be the same though.

 

[SCORPIO]

It looks like 1.47 is what SEI offers as a replacement for the 1.50 which is what Merc used on all the 5.7s, at least from what I can find on the SEI site. Thanks for confirming what is in yours, that reassures me I'm on the right track.

 

[Lazy Daze]

Have you checked the prop chart on Sea Ray's website? It also lists drive ratios.

What is your engine serial number?

 

[Strecker25]

Should be 1.47 for the 350s, same as mine

Just a word on SEI and our experience. We have SEI Lowers on our 98 290 DA with twin 350s. They we’re installed by the dealer I purchased from in 2015. The first year was fine, we put 50-60 hours on them. I removed them for the winter, changed lube, pressure tested, all looked good.

The next season we were cruising along at 25knots and experienced catastrophic failure of the stbd side. Turns out the pinion gear blew up and nearly flew out the side of the drive. They were still under the 3 year warranty. I hauled the boat, removed the drive and sent back to SEI, about 2 weeks out of the water and I got the replacement and re-launched and finished the season without issue. They said the failure was result of improper break-in. The break in period is 10 hours of varying rpm up to planing speed around 8 hours. I followed it religiously and that side has been healthy since.

Last season I was putting to the gas dock at idle speed. A loud bang and a stalled port motor I thought I hit something. Same drawn out process as above but this time the clutch mechanism failed
and locked the lower, in turn shearing the vertical driveshaft off clean where it enters the upper. Again replaced with two weeks downtime, followed the break in period again, and no problems the rest of the season. SEI again blamed improper break in for the failure. I also had to replace the shift shaft bushing and the oil seal under the impeller on the replacement lower because they leaked with ZERO hours on them.

The moral of my story is
1) their warranty is good; they honor it, but it’s not fast.
2) I’m not sure if I got unlucky, or since the dealer didn’t mention the break in period when I bought it, but I’m hesitant to recommend their product on boats our size. Having both blow up really sucked, and I baby the hell out of the throttle in our boat

Plenty of people have nothing good to say about the product, but shop around and maybe consider OEM uppers if you can find some CPO drives.

 

[NorCal Boater]

I have an SEI 106 complete drive on my '85 Cobalt. No, my boat is not as large as you guys but my motor is a GM 383 Stroker of undetermined horsepower. Estimates are somewhere north of 350. Everything I have been told says that's a problem for a Merc Alpha I. SEI stated on another forum that their drive could handle that HP and torque. The drive has been on for the past 5 years. Admittedly, the boat has had minimal use the past 2.5 years as I am just finishing an extensive resto-modification. But the idiot previous owner had no problems. I have not heard anything bad about their drives and I would not hesitate to buy another if I needed one.
Shawn

 

[Strecker25]

I have an SEI 106 complete drive on my '85 Cobalt. No, my boat is not as large as you guys but my motor is a GM 383 Stroker of undetermined horsepower. Estimates are somewhere north of 350. Everything I have been told says that's a problem for a Merc Alpha I. SEI stated on another forum that their drive could handle that HP and torque. The drive has been on for the past 5 years. Admittedly, the boat has had minimal use the past 2.5 years as I am just finishing an extensive resto-modification. But the idiot previous owner had no problems. I have not heard anything bad about their drives and I would not hesitate to buy another if I needed one.
Shawn

Glad to hear success stories too. Like i said, I’m sure plenty of people have good luck with them. At the same time I’m sure plenty of OEM drives have failed over the years as well

 

[SCORPIO]

I have a counter rotating SEI lower on my port drive, been on for 4 years, has worked fine to date. I know SEI has mixed reviews, but considering the price, I may opt for one. I want to see if I can somehow true up the mating surface so the gasket can do its job. I've thought about using a double gasket but am afraid that may cause more issues than it solves. I also thought about gasket sealer but that area is just so narrow there isn't much room to even put any gasket maker. It certainly looks under engineered to me.