alpha 1 Gen 2 sterndrive broken lower drive shaft

alldodge

alldodge

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With 24/24 upper gears and 13/21 (gear pic above) lower it would be 1.62 depending on which year. To get 2.0 need to have 14/28 gears

Alpha Gen 2 gear ratios.jpg
 
Scott06

Scott06

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akdad said:
Ok, took upper set apart on old unit and counted teeth 24-24 with s/n 0L119519 sterndrive which is either 1.62 or 2.0 ratio which means I was sold wrong ratio of 1.47. Must have been too stressed out....now second guessing what i remember of W.O.T. setting I had with newer outdrive and prop. I know it was dialed in with old outdrive and 5.7L w/15p prop.
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You have had the exact same results with two different gear ratios so I don't think the ratio is the issue. If you did switch from 1.62 - 1.47 that would only drop WOT rpm like 400 assuming you were propped correctly before so may have sent you from the top top bottom of WOT rpm range..but you are better for engine health being under propped than over propped...

I would think the gear is chipping then locking up the drive which breaks the shaft. If your upper looks ok you could get away with a new lower (could try an SEI) and maybe see if you can use a higher performance lube. This may be the low road... had a similar situation at work with centrifuges eating gears in drive, after replacing the second set the manufacturer recommended using a Mobil gear oil for higher stress environments and never had an issue again except lube cost...

They make this lube https://www.mertenmarine.com/mercury-racing-gear-lube-1-quart-8m0078015 would think this or something out of an offshore go fast environment would help.

Just trying to think of an options besides going to a bravo but that may long term be the best bet
 
akdad

akdad

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Jun 22, 2010
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Scott06 said:
You have had the exact same results with two different gear ratios so I don't think the ratio is the issue. If you did switch from 1.62 - 1.47 that would only drop WOT rpm like 400 assuming you were propped correctly before so may have sent you from the top top bottom of WOT rpm range..but you are better for engine health being under propped than over propped...

I would think the gear is chipping then locking up the drive which breaks the shaft. If your upper looks ok you could get away with a new lower (could try an SEI) and maybe see if you can use a higher performance lube. This may be the low road... had a similar situation at work with centrifuges eating gears in drive, after replacing the second set the manufacturer recommended using a Mobil gear oil for higher stress environments and never had an issue again except lube cost...

They make this lube https://www.mertenmarine.com/mercury-racing-gear-lube-1-quart-8m0078015 would think this or something out of an offshore go fast environment would help.

Just trying to think of an options besides going to a bravo but that may long term be the best bet
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Thanks! I think gear chipped after failure.
 
T

tank1949

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akdad said:
Scratching my head on this on! I have had 2 broken lower drive shafts break on 2 different outdrives. Last one was a complete new Mercruiser outdrive 2017 1.47 ratio with mercury 15p AL prop and Mercruiser 5.7L 250hp. Did not hit anything, same prop on both, looks like new. Anyone else run across this problem? Is my luck that bad? Long slow trip back to harbor on kicker x2 ...NO fun! Shaft#45-853648View attachment 370214
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I've seen this happen when boaters jump waves and motors rev high and then boat comes back down (OD) where water jams the prop. Still very rare.
 
H

havoc_squad

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There must be some activity being done that is abruptly increasing or slowing RPM against the prop shaft load.

Do you aggressively shift from forward into reverse or vice versa while still in motion too quickly in no wake areas and goose the engine to correct maneuvering mistakes?

On a heavy boat going fast for no wake speeds I could definitely imagine gearbox stress happening if done often if the operator gooses it after shifting to correct on a frequent basis.
 
akdad

akdad

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havoc_squad said:
There must be some activity being done that is abruptly increasing or slowing RPM against the prop shaft load.

Do you aggressively shift from forward into reverse or vice versa while still in motion too quickly in no wake areas and goose the engine to correct maneuvering mistakes?

On a heavy boat going fast for no wake speeds I could definitely imagine gearbox stress happening if done often if the operator gooses it after shifting to correct on a frequent basis.
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Not hard on this boat. Had since 2008, repowered from 5.0L 220HP to 5.7L 250HP. Boat weights approx. 6500lbs full of fuel and 4 people at most on board. Never full throttle, ease up to get on step. Cruising about 28mph in calm seas both times. Never panic stops or docking. Normal Senior boater.
 
Scott Danforth

Scott Danforth

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akdad said:
Not hard on this boat. Had since 2008, repowered from 5.0L 220HP to 5.7L 250HP. Boat weights approx. 6500lbs full of fuel and 4 people at most on board. Never full throttle, ease up to get on step. Cruising about 28mph in calm seas both times. Never panic stops or docking. Normal Senior boater.
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Boat that big needs a bravo and a big block.

My guess is the drive is at its limit with that large a boat
 
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