470 vs alpha one

aussie · #1 03-21-2011, 06:51 PM

not sure if what im saying is rite but what is the difference between my 470 leg and a alfa one

please explain

THEFERMANATOR · #2 03-21-2011, 10:43 PM

The ALPHA one leg came out some time in the early 80's(82 I think) and was the lower unit used behind everything from the little 2.5L 4 banger up to the 350 small block at 260HP. Before the ALPHA there was the MR I believe it was which for the most part interchanges with the ALHPA one. Your 470 probably has an ALPHA 1 behind it.

spareparts · #3 03-22-2011, 06:05 AM

ferm got it right on the Alpha year models. the upper unit between the two(Alpha and MR1 are simular, MC1 was the older units) didn't differ that much internally, they did differ cosmetically outside. ALl ALpha units also had the large trim cylinders, MR1 units had the odd skinny trim cylinders. the lower unit was where the difference was, the tapered drive shaft bearing was flipped over hte the lower gears were cut different to allow the gear load to push against hte upper bearing. The older MC1 lower units had a preload pin inthe top of the drive shaft that forced the shaft down against teh tapered roller bearing till the gears were under full load, pulling the bearing down, the Alpha(and MR1) didn't have the preload pin, the gears pushed apart against the tapered bearing(bearing installation was flipped). Just about any of the units are swappable, just keep in mind which trim cylinders you are using, and which ratoi you want to end up with. Some early alpha and MR1 units had an A stamped on the propshaft to designate it being an Alpha. Some early 80's 4 cylinder units looked like an Alpha on the outside(square top cap, large trim cylinders), but actually had the older MC1 style internals in the lower(look for the A stamped on the shaft). Alpha units were suposed to be 7 times stronger than the MC1 units. If you have any reason to replace the lower unit, I sugest you upgrade to an Alpha, it will bolt right on.

aussie · #4 03-22-2011, 10:54 AM

thanks guys again for the info

moneyhole · #5 04-07-2011, 09:34 PM

Stern Drive Engineering has a complete stern drive unit minus prop with a 3 yr warranty, they claim no matter if you hit a stump or fishing line, for the MR l (pre-Alpha) and the Alpha 1 for $1295. MR l & Alpha 1 use the same unit. That's the route I'm going... selling a couple of dirt bikes and an old Triumph 500 and I'm ordering that unit. I think they call it the SR106. Just need to know what ratio you want (1.62 for me) and it's on the delivery truck. I have talked to them a couple of times and they seem like very nice folks to deal with- very helpful and have all the answers to my questions so far

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moneyhole · #6 04-10-2011, 11:17 AM

Where did the Merc 888 outdrive fit in with the MR1 and the Alpha(s)? Is the 888 also an Alpha unit and if so about what dates were they manufactured? Was it made for the larger displacement engines?

By the way guys, the info on the MR1 and Alpha is very helpful. I also have a complete Merc outdrive that has the reverse lever on it, how far back does that date? I have everything...someone just cut out a section of the transome with a sawzall to get it. So if anyone has a need for a really old outdrive, I'm going to post it in the classifieds section. Thanks again!