Weak Link in Alpha One?
 

What is the everyones opinion on the weaklink with the alpha? Is it the Upper or Lower unit? I realize that they both have limits. According to my mechanic my lower unit may need some "freshing-up". Nothing major though. Im running a 360hp small block. Im not sure on my ratio though. I was running a 270hp with a 17pitch 3blade stainless and ran 4900 rpm's. I guessing it's probally a 1:32.Best speed was 50mph(GPS)with approx 4000lbs loaded. Finally I have heard so much on a supposed set of HD gears for the alpha...Most of what I have heard is that the newer gearsets are all HD. Originaly only the 1:32 gears were HD....Also what puts more load on the outdrive a 1:3 or 1:5 ratio.....Oh well lots of questions hope I can get some input...Thanks in advance

BirdDawg
86F3LS 360hp SB Alpha One

I'm not sure where the 'weak link' may be since I've never failed one. I have an '86 242LS with twin SBC's- about 350 HP each on Alphas.
I installed Simrek drive showers, Merc drive reservoirs, and run RedLine ShockProof Heavy lube in them, and have had no problems, and I do run them fairly hard. I think those three things have a lot to do with keeping them healthy.
I've heard the only hotter running outdrive than the Alpha is the BravoIII. Cooler lube, avoiding holeshots, and avoiding going airborne will give 'em a long life. :D ;)

I've had two fail the same way. The shaft coming from the lower into the upper - snapped where the O-Ring fits on the spline.

Alpha weak spot..
 

I come from a family of Metalurgist that all happen to be boat nuts as well. We have talked about this a few times and also with Hi-Po engine buiders and it always comes back to the upper unit...not the gears or the shaft because there are metalurgical ways to work around that (i.e. anealing, case hardening, etc.)

The weak spot is the case that houses the bearing races that support the gears and shafts. The big initial directional change happens at that 1st 90 deg directional change of force. The aluminum case and the way it is shaped has limits as to the force it can withstand. Once the case distorts then the allignment of the gears change. Every thing gets "out of whack" and failure happens quickly after that distortion occurs.

Heat is aluminum's enemy more so than it is to steel or iron.
That's why drive showers are so effective...they remove the heat build up in the upper unit case structure and prevent the weakness from heat. The shock of big torque and sudden acceleration/decelleration (i.e. "catching air") however will distort the case beyond recovery and you get total failure. Compare the bulk of material used in a Bravo vs an Alpha in the drive shaft housing....Captain Obvious...OK? Even as good as Bravo XRs are...builders like Tom Hofstetter at Chief Engines tears them down right out of the crate and puts in ALL HD bearings, races, shafts,etc. If a drive has a part that can be broken, Tommy has made it break...we all learn from this.

So...if some one wanted to build a "Super High Tech Double Throw Down" bullit proof Alpha, they would start by building the case or housing of the upper unit from hi-strength stainless steel. Add to that heat treated gears and forged shafts and you would have something very strong for sure.

Then...we would start spinning out couplers, shearing off bolts holding fly wheels to crankshafts or worse still...break the cranks themselves.:eek:

Man learns from pushing machinery to it's point of failure and then raising the bar to the next point of failure....a natural process:cool:

I've failed the upper gearset so that is the weak link for me :). Running about 425hp...twins.

I think the posts above probably answer your question.

I ran 350hp on the grooved vertical shafts without failure, but since have changed them out to ungrooved. I broke 3 transom bells before going to a counter rotator on port drive.

Anyway...I would-

1) Install drive showers
2) Install vertical shaft w/o oring groove
3) Change oil regularly

Nice to do

1) My drive guy increased bearing pre-load on upper gear box bearing
2) Updated gear sets..don't recall the details..I replaced one set when drive apart for other work- Maybe more alpha info here..http://www.speedwake.com/forums/arch...p/t-60343.html or some info on ratios..http://www.sterndrives.com/mercruisersterndrives.html
3) Remove upper unit shaft seal (if upper box apart) and convert to wet spline (vert shaft) with double lower seal
4) Renew shifting dog "pre-load springs" in lower unit if apart..drive will pop out of gear under load..

Have fun.....

Just noticed the original post is 10 yrs old..hopefully he has Bravos now ;)