Complete Swap - Alpha One Gen One to Alpha One Gen Two

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I have a 1988 Invader Ski boat I have been restoring. Had it out the other day and the universals went postal on me. Damage is substantial. Gimbal is broken. Upper housing is cracked. Replacing the entire drive system seems the best solution.

The dead drive is an Alpha One Gen One. I found an Alpha One Gen Two complete drive for a reasonable price.

My question is can I bolt the Gen Two onto the transom where the old Gen One drive is? I'm not anticipating using any of the Gen One parts. Just need to know if this is an option.

Thanks,
 

Rick Stephens

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Everything aft of the boat's transom should be swapped. Gimbal housing, bell housing, drive and all. The inner transom plate is the same, so you can change it or leave it. You probably have to drill a couple holes at the top of the keyhole. Other than that, it's a direct swap in.
 

Bondo

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Ayuh,.... As Rick says, just drill 2 more 1/2" holes at the top of the keyhole, 'n yer Golden,.....
 

fishtails

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If it's ever been kept in a slip (and maybe even if it hasn't) be prepared for a possible transom replacement. I'm going through that right now. Just cross your fingers when you pull that gimbal off and good luck!
 
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After a little research I bailed on the used drive.

A little history.

When I acquired the boat it had a 5.0 Chevy in it. The block was cracked on the outside, but nothing letting water in the oil. A wire wheel on a mini-grinder and a bit of Bondo bought me two years of use.

I hadn't noticed the motor mounts, made of wood, had turned to mulch inside the fiberglass casing formed around the wooden blocks used to bolt the motor mounts to. Near the end of the boating season the coupler failed due to radical misalignment from the rotted shims under the motor mount. When I pulled the engine I saw cracks on the starboard exhaust manifold, plus the bondo was beginning to delaminate from the block on the port side. I thought it would be wiser to replace the engine since I had it out.

I pulled all the decayed wood out and filled the fiberglass casing that was left with kitty litter saturated with fiberglass resin. (I know it sounds absurd. You'll just have to trust me that it worked.) I used 1" thick polyethylene shims bolted to the restored mounting blocks.

The motor I put in is a 5.7 Chevy marine engine with some modifications by an qualified engine machinist. Bit of a cam, Edelbrock Performer manifold. Oversized pistons. Puts out in the range of 330 HP and with my current prop spins at an appropriate ~4,800 rpm. However I'm assuming the hp is probably what caused my ancient and original Alpha One Gen I drive to self destruct.

I just love the boat, have a little over $7K in it, and am not adverse to dropping what I have in it again to upgrade the drive. I have read where the Alpha One Gen II is capable of 65mph, which is about top end at WOT currently, but am concerned that even if I go with a new Gen II that it's not enough to provide reliability as it's advertised at maximum 300 hp.

My next uneducated question is can I put a Bravo One in the same transom...or would a new Gen II be enough. I don't want to tear this apart again.

Y'all can tell me I'm crazy to consider it, however I could use some sound advice here.

Thanks,
 

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Bondo

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My next uneducated question is can I put a Bravo One in the same transom...

Ayuh,...... Welcome Aboard,..... Basically, everything aft of the fiberglass transom is different with a Bravo,.....
'n ya need a motor driven raw water pump,.....

Reliability will be up to the right hand of the operator with an Alpha,......
 
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Rarely more than a minute at WOT.

Is acceleration a factor? Floor it and it 'pops' out of the water, throttle it back to 2,600 to cruise at 35mph, which would be normal.
 

harringtondav

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Engines produce maximum torque 3500-3800 RPM. And torque is the limiting factor in a drive"s design. Bondo 's right hand is most critical @ hole shot. Once.you're on top of the water torque loads drop.
 
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So, if I want to floor it coming out of the hole, the Gen II isn't enough? I can tell you that from my cruise speed of 2,600 an aggressive acceleration will compress the seat you're in. I can't promise myself I won't do that. Sounds like more $$ for more reliability.
 

harringtondav

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So, if I want to floor it coming out of the hole, the Gen II isn't enough? I can tell you that from my cruise speed of 2,600 an aggressive acceleration will compress the seat you're in. I can't promise myself I won't do that. Sounds like more $$ for more reliability.

Merc advertises their Alpha Gen II up to 300 hp. But their current line up ends with 250 hp 4.5L, and jumps to to 350 hp 6.2L, which I suspect is coupled to a Bravo.

So It's get back to torque. I'd find a Alpha Gen II that is geared for a 350 Mag. 1.47:1 AKA 1.50:1. 1.62:1 as a fall back. These drives are designed for V8 HP (which is torque X RPM /5252). I'm SWAGing the Alpha ll is good for 260-275 ft lb of torque max. And your on-steroids 5.7 sounds like it could exceed this under some conditions.

So like any other machine, the harder you push it, the shorter life expectancy. So try to control your adrenaline rushes, or you will be replacing your $370 drive gear set and/or $200 FWD gear set with every other lube change. ;)
 

harringtondav

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I pulled all the decayed wood out and filled the fiberglass casing that was left with kitty litter saturated with fiberglass resin. (I know it sounds absurd. You'll just have to trust me that it worked.) I used 1" thick polyethylene shims bolted to the restored mounting blocks.

FYI. I had to excavate under my front mounts due to 3 of 4 lag bolts twisting off as I was replacing a frozen mount - spun when adjusting. I used West System 105 Resin, 207 special clear hardener, and their 404 High Density filler. I'm impressed... just in case you need to build new mount risers for your V8.

I also used SS hanger bolts to secure the new front mounts. I doubt/hope I'll never need to remove them again. But if I do it will be as easy as removing four 3/8 nuts.
 
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@ harringtondav: Thanks for the briefing on the torque. I'm still wrapping my head around how the drive can be so torqued when there's just a prop spinning in water. I have no doubt I need to accept your explanation...I just don't get it. I can move 200 lbs. of water just by jumping in it.

On your FYI, it is curious to me why there would be wooden anchors for motors to begin with in vessels that certainly get water in the bilge from time to time.

I used regular Bondo fiberglass resin available at pretty much any hardware store.Only took a gallon with 'clumping' kitty litter to create the medium to anchor the motor mounts. To give me more time I only used about 2/3 of the hardener required. It took a little longer to set up but the voids where the rotted wood was removed were still pretty stout. Once they were filled with the resin mixture they turned out at least as solid as wood would have been. I drilled 11/32" holes and used 2 - 6" x 1/2" stainless lags to anchor each of the motor mounts through the polyethylene shims. In my view it is rot proof now.

Moving forward; I am likely to install a Bravo One if only so I don't have to forfeit the adrenalin rush. I know it's adolescent, but I refuse to grow up, and frankly, I get a thrill out of it.

@ achris and Bondo: I appreciate your honest comments; even though I don't like their implication. I was looking for simple answers, and although you did answer my questions simply, they weren't the answers I wanted. I wanted someone to tell me to just put the Alpha One Gen I back on and you'll be good with your exuberant habits. Clearly that's not the case. So...I have sourced a rebuilt Bravo One, again for a reasonable price, although twice that of a rebuilt Alpha One. And, if you will help me further, I have more questions for y'all to make sure I only do this once:
  • Do I need to change the transom plate on the inside? The rebuilt drive I found comes complete with the transom plate, hoses, trim cylinders, oil reservoir, trim pump, gimbal assembly. The whole shebang.
  • Will my existing throttle/shifter work with the Bravo One?
  • Will my existing power steering system that works on an Alpha bolt onto a Bravo?
  • The 5.7 has v-belts. I found a v-belt raw water pump, bracket and pulley. The current configuration pumps water through a power steering cooler before it goes to the engine water pump. Clearly the incoming water comes through the Bravo Sterndrive. Do I then connect the pumped water to the power steering cooler?
I appreciate your help in this.

Thanks,
 

harringtondav

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@ harringtondav: Thanks for the briefing on the torque. I'm still wrapping my head around how the drive can be so torqued when there's just a prop spinning in water.

Thanks,
My hands-on w/torque is from the tractor diesel world. You hook a dyno to the PTO shaft, start the tractor and set it at WOT idle, 2200-2300 rpm!! Then start applying load until the rpm drops. That's your 'rated' torque. Turbo diesels are cool, because as you increase torque resistance the rpm drops, the ECU starts dumping more fuel, and the torque rises - until it kills.

I suspect gasoline engine torque is mapped the same way. Dyno load at a fixed rpm to maintain that rpm, more fuel & higher rpm and another torque point on the curve.

I have no idea how Merc. rates their drives. I respect their engineering and suspect they dyno test their drives to what's called a B10 reliability goal (10% will fail). My employer had a 10K hr. goal. I'd guess Merc is at least 1000 hrs.

If you consider the thrust required to launch your boat our of the water and compress the seat upholstery, overcoming your boat's weight and drag, it's all coming from torque applied to your prop.
 

Bondo

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  • Do I need to change the transom plate on the inside? The rebuilt drive I found comes complete with the transom plate, hoses, trim cylinders, oil reservoir, trim pump, gimbal assembly. The whole shebang.
  • Will my existing throttle/shifter work with the Bravo One?
  • Will my existing power steering system that works on an Alpha bolt onto a Bravo?
  • The 5.7 has v-belts. I found a v-belt raw water pump, bracket and pulley. The current configuration pumps water through a power steering cooler before it goes to the engine water pump. Clearly the incoming water comes through the Bravo Sterndrive. Do I then connect the pumped water to the power steering cooler?

Ayuh,...... Ya need All of the Bravo, from the rear motor mounts, Aft,.......

Ya, the controller will work, but the switch on the shift plate 'tween the shift cables is not used,.....

P/S oughta swap, no problem,.....

'n the raw water comes in through the drive, through the cooler, then to the raw water pump,.....
 

Bondo

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Ayuh,..... Got yer pm, 'n can open the link, so ask away here,......

I've been wrong before, 'n no doubt will be wrong many more times,.....

Besides, like Any plumbin' job, there's more than 1 way to get it done, probably several ways that'll work perfectly,......
 
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