Lesson on Outdrives

Socks

Member
Jan 7, 2019
45
Boat Info
1983 Sea Ray 270 Sundancer.
Engines
Twin 5.0L (305 ci) Mercruisers
How do i determine what series of outdrives I have? They are Mercruisers, but I can't find anything showing if they are Alpha, gen1 gen2 -- or Bravos etc.

Also, is there a difference between the Port and Starboard?

Thanks
 
Show us a picture. Someone will be able to identify it.

Also google “Mercruiser outdrive identification”. There is info out there with pictures.
 
You will need to look for a serial number. Based on the year of your boat they may not be Alphas but rather "pre-Alphas." I think the Alpha drive was introduced in 1984. There is a chance a previous owner upgraded them. A couple of pictures of your drives would help.

The serial numbers would also reveal whether one of them is counter-rotating and if this is true it definitely makes a difference in port or starboard.

Post a of pics of the drives and I should be able to tell you where to look for the serial numbers.
Shawn
 
Thanks, I'll get pictures tomorrow
 
The serial numbers would also reveal whether one of them is counter-rotating and if this is true it definitely makes a difference in port or starboard.

I was under the impression that the counter rotation was achieved by altering the external shift mechanism and the internals were identical.

Can you elaborate further on the differences?

No sarcasm here, I’m just curious as to how it works.

Thanks.
 
I was under the impression that the counter rotation was achieved by altering the external shift mechanism and the internals were identical.

Can you elaborate further on the differences?

No sarcasm here, I’m just curious as to how it works.

Thanks.

The counter rotation on Alpha 1 Gen 1’s is in the lower unit. It’s a different case and gears than a standard rotation. If you install one (I did this on my old boat) you also have to make a change at the shifter.
While counter rotating units are fairly common in Alpha 1 Gen 2’s, they can be hard to find in OEM Gen 1’s.
It took me a while to find an OEM one for my old boat which was an 87 300 Sundancer.
SEI does make an aftermarket counter rotating Alpha 1 Gen 1.
I don’t know if they ever made a counter rotating Pre-Alpha.
 
The counter rotation on Alpha 1 Gen 1’s is in the lower unit. It’s a different case and gears than a standard rotation. If you install one (I did this on my old boat) you also have to make a change at the shifter.
While counter rotating units are fairly common in Alpha 1 Gen 2’s, they can be hard to find in OEM Gen 1’s.
It took me a while to find an OEM one for my old boat which was an 87 300 Sundancer.
SEI does make an aftermarket counter rotating Alpha 1 Gen 1.
I don’t know if they ever made a counter rotating Pre-Alpha.

Thanks for the clarification.

What about Alpha I Gen 2’s and Bravo’s? Same situation?
 
Mitch, thanks for the info. I like anything with pictures :) --- However, I am more confused.
Pre-Alpha's (according to the info, has a hump on the top plate and has a ribbed area at the vent screw. Mine is flat on the top and a non-ribbed (smooth) area at the vent. So it indicates I have Alpha 1.

But, this is where it gets confusing. The Alpha 1 info states the cavitation plate is square on the Alpha1 and mine are rounded indicating it is a Pre-Alpha.

Is it possible I have a Alpha1 upper and a Pre-Alpha lower?

Thanks
 
I forgot to ask, where do I find the serial numbers? Does the fact that my props are marked R & L indicate one drive is counter clockwise rotation?
 
I forgot to ask, where do I find the serial numbers? Does the fact that my props are marked R & L indicate one drive is counter clockwise rotation?

When you look at the props, are the blades on one curved in the opposite direction?
 
Espos4, I stand corrected, the props are not marked R & L. I mis-read and they appear to be the same --- Only difference in the numbers, -- 1 ends in A and the other in B.

Thanks for the help.
 
I forgot to ask, where do I find the serial numbers? Does the fact that my props are marked R & L indicate one drive is counter clockwise rotation?
The serial numbers would have been affixed to the outside of the drives and are probably long gone.
Post a picture of your drives and someone can help you identify them.
 
Thanks for the clarification.

What about Alpha I Gen 2’s and Bravo’s? Same situation?
Gen 2’s were available in counter rotation in all years, and like the Gen 1’s, the case for the lower unit is slightly different on the counter rotating drives. The untrained eye would only notice the slight difference if a counter and standard rotation drive were closely examined right next to each other.
I had to have it pointed out to me.
I’ve got no experience with Bravos
 
The serial numbers would have been affixed to the outside of the drives and are probably long gone.
Post a picture of your drives and someone can help you identify them.
I also had the complete drive #'s with transome #'s on both of my drives attached to both of my motor tags, don't know if this was normal or not but they were merc cruiser tags.
 
I also had the complete drive #'s with transome #'s on both of my drives attached to both of my motor tags, don't know if this was normal or not but they were merc cruiser tags.

Those were probably on removeable covers which, judging by his inquiry, I’m guessing are long gone from the OP’s 36 year old boat.
 

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