Newtoboatingyanmar
New member
Can someone help me identify the model of my outdrive please 
Outdrive model identification plz
- Thread starter Newtoboatingyanmar
- Start date
MapisM
Well-known member
Mercruiser Alpha Gen 1
Newtoboatingyanmar
New member
Thank you mapism I needed to know as it needs a bit of an overhaul so I may post for info as the project goes on ie anodes hydraulic cylinder etc
ChromeDome
Well-known member
Serial number sticker with gear ration info is/was on the side of the upper leg (exact location differs with year/version).
Commonly painted over with antifoul
Commonly painted over with antifoul
Ribtecer
Well-known member
Please do, I'd be very interested to see the work. ?
spannerman
Well-known member
That is absolutely not an Alpha drive, its a Bravo 2 . Alpha drives don’t have the rear cover plate, only a cover on the top of the drive.
QBhoy
Well-known member
Agree it’s 100% a bravo 2, as said above.
stelican
Well-known member
Yes the lower unit size gave me that impression but did not want to be proved wrong!
QBhoy
Well-known member
Spot on. Props tend to be very expensive for them…likely because they tend to be mostly uniquely suited for only the bravo 2 and not generally able to be easily (if at all) used on other applications. As far as I know at least.
ChromeDome
Well-known member
I'm sure the Bravo and Alpha share same Flo-Torq Hub kit
835257Q 1
so should use same propellers (=same cost).
835257Q 1
so should use same propellers (=same cost).
QBhoy
Well-known member
Alpha and bravo one can share props. Bravo 2 not so much. Almost sure the bravo 2 doesn’t have the same prop shaft either. Larger and maybe even different spline pattern too. Most of the props for them are fixed/integrated hub things, that I’ve seen anyway.
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spannerman
Well-known member
B2 has a much thicker propshaft and the props are much larger diameter than the other drives. Its a drive for designed for swinging a large slower prop where the drive is under max load all the time on halfplaning hulls where the boat doesn’t make it over the hump. Alpha and B1&3 are for fully planing boats where the torque load drops off once you are up on the plane.
Elessar
Well-known member
Bravo 2 the most bullet proof of the Mercruiser drives.
Also the big props make them handle most like a shaft drive as it has noticeable prop walk. Still best handled with the wheel but you can get the most out of using the engines to manoeuvre.
With all of their drives Mercruiser sell a blanking plate for the cooling water when being used with Diesel engines as there isn’t enough flow through the leg. So a skin fitting is used.
If it is installed like this then change it to a Y, so water comes in through the leg and through the skin fitting.
Water flow through the leg helps keep it cool.
Also fit a drive shower.
Otherwise on extended passages on the plane when the leg is mostly out of the water they overheat and when you come off the plane and dunk them in the water the shock cooling can cause damage.
From experience
Also the big props make them handle most like a shaft drive as it has noticeable prop walk. Still best handled with the wheel but you can get the most out of using the engines to manoeuvre.
With all of their drives Mercruiser sell a blanking plate for the cooling water when being used with Diesel engines as there isn’t enough flow through the leg. So a skin fitting is used.
If it is installed like this then change it to a Y, so water comes in through the leg and through the skin fitting.
Water flow through the leg helps keep it cool.
Also fit a drive shower.
Otherwise on extended passages on the plane when the leg is mostly out of the water they overheat and when you come off the plane and dunk them in the water the shock cooling can cause damage.
From experience
spannerman
Well-known member
The blanking plate is an option, most of the diesel engine boats we service do not have the blanking plate fitted, there is sufficient flow for all the engines from 120 hp 4 cyl through to 6 cyl D320hp. The are only a few I have seen in the 26 yrs with Mercruiser and they were Yanmar engines with Bravo drives and a few other odd exceptions.
If the blanking plate is fitted it is essential the the S water hose from the drive to the transom has 2 inches cut out of it, this allows the water that would be forced into the drive inlet to circulate through the drives cooling passages and then exit. I have seen several installations where the hose wasn’t cut by the person doing the installation, this results in the gear oil getting too hot and thin, so hot that I have seen the paint on the outside burnt! A drive shower is recomnended on heavily loaded drives or boats that plane with most of the drive above the water level. I spesialise in Mercruiser and Volvo drive rebuilds and its not pretty inside when the drive has been run with oil that got too hot.
If the blanking plate is fitted it is essential the the S water hose from the drive to the transom has 2 inches cut out of it, this allows the water that would be forced into the drive inlet to circulate through the drives cooling passages and then exit. I have seen several installations where the hose wasn’t cut by the person doing the installation, this results in the gear oil getting too hot and thin, so hot that I have seen the paint on the outside burnt! A drive shower is recomnended on heavily loaded drives or boats that plane with most of the drive above the water level. I spesialise in Mercruiser and Volvo drive rebuilds and its not pretty inside when the drive has been run with oil that got too hot.
MapisM
Well-known member
Apologies to the OP, spannerman is correct.
I didn't notice the rear cover, and I assumed that the straight lower unit was only ever used in the Alpha Gen 1, but obviously I was wrong.
Elessar
Well-known member
Mine was fitted to a Yanmar and destructed after coming down off the plane after a 100 mile cruise. I guess it didn’t have the 1” cut. You are right it wasn’t pretty at all.
I then got a boat with twin 220 Mercruisers on bravo 2s. I didn’t regret retro fitting the Y input to get flow through the drives.
spannerman
Well-known member
About 15 yrs ago we had a spate of drive failures when coupled to Yanmar engines, then Mercruiser issued a bulletin only approving certain Yanmar/Bravo combinations and they had to have a drive shower installed, after that we had no problems.
Ribtecer
Well-known member
Blimey, I have an Alpha One leg on a 7m Rib with a cummings 150hp diesel, it has a skin fitting providing the cooling water direct to the engine only.
Should I be concerned?
Many thanks in advance.
Should I be concerned?
Many thanks in advance.
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Elessar
Well-known member
I’d take spannerman’s advice about the 2” cut seriously and check it was done.
spannerman
Well-known member
Double check you have the blanking plate installed first, look at the back of the engine and right above the driveshaft there should be a black oval plate with two bolts on the insude if the transom frame, if there is a hose connected to a fitting check where it goes. It will be connected into the hose from the skin fitting, if so do not cut the external hose.
Having established you have a blanking plate then trim the drive up and cut 2 inches out of the big hose on the lefthand side taking care not to cut the speedo pitot hose or trim sender wire which are usually clipped to it.