Mercruiser outdrive failure & replacement

[Denise K]

Looking for some knowledge and expertise here about an outdrive failure and if something specific may have caused it. Last year, at a reasonable cruising speed, we suffered complete failure of the outdrive. Within a few seconds, it got very loud, the engine died and wouldn't restart. Upon removing the outdrive, it appears that the gears inside were basically destroyed (will attach pics). Once the outdrive was removed, the motor would turn over and run so hopefully no damage to it. We replaced the outdrive ourselves with a new one from Mercruiser (lengthy backorder from SEI and needed to get back on the water in a week). We replaced both the upper & lower on assumption that the chunks of metal from the gears in the upper were likely all through the lower unit too.
Now the questions:
1) Could something underlying have caused this or is it possible it was just "metal fatigue"? Don't want to have to shell out another $3500 if we didn’t fix the root cause here.
2) There's (to me) noticeable vibration at low RPM's, does the outdrive need aligned somehow or otherwise adjusted if replaced? Hubby is very mechanical but not an 'outdrive guy', so if there are some details/activities surrounding the outdrive replacement, I want to be sure we're checking the boxes.
Thanks for any help/suggestions any of you can provide!

 

[nola mike]

Looking for some knowledge and expertise here about an outdrive failure and if something specific may have caused it. Last year, at a reasonable cruising speed, we suffered complete failure of the outdrive. Within a few seconds, it got very loud, the engine died and wouldn't restart. Upon removing the outdrive, it appears that the gears inside were basically destroyed (will attach pics). Once the outdrive was removed, the motor would turn over and run so hopefully no damage to it. We replaced the outdrive ourselves with a new one from Mercruiser (lengthy backorder from SEI and needed to get back on the water in a week). We replaced both the upper & lower on assumption that the chunks of metal from the gears in the upper were likely all through the lower unit too.
Now the questions:
1) Could something underlying have caused this or is it possible it was just "metal fatigue"? Don't want to have to shell out another $3500 if we didn’t fix the root cause here.

Most common cause of self destruction is low gear oil. Was that changed/checked? I'm assuming that you have a 1986 alpha one like me. But yeah, sometimes things fail, especially after 36 years.

2) There's (to me) noticeable vibration at low RPM's, does the outdrive need aligned somehow or otherwise adjusted if replaced? Hubby is very mechanical but not an 'outdrive guy', so if there are some details/activities surrounding the outdrive replacement, I want to be sure we're checking the boxes.
Thanks for any help/suggestions any of you can provide!

The engine should be aligned whenever the outdrive is removed. Misalignment will usually trash the coupler, but could cause vibration. U-joints/gimbal bearing are the other usual suspects. Assuming u-joints are new, did the gimbal get checked? Was any water in the bellows?

 

[achris]

You need to identify the drive and engine to us.

If it's an MC1, then there is another underlying problem the upper gears suffered from. The later driveshaft housing gears were cut differently (stronger) and that problem went away (mostly)..

Chris...

 

[achris]

Ok, that's a Gen II drive (I was using the phone earlier and don't bother even looking at pictures of the phone )...

That's also a cracked tooth that's come away, unlikely to be lack of oil. Lack of oil overheats the gears, and they melt, literally!

So, what caused the crack? Did you, sometime in the last (about) 50 engine hours have an instance where the engine stalled due to rope fouling the propeller, or a sandbar strike, or something like that? Something that would have caused the engine to stall while the prop was loaded. The last thing any engine does as it stops is to 'kick-back'. When the prop's loaded when the engine kicks back, the back side of the gear teeth get a hard hit, an it cracks the tooth root, and it takes anything up to 50 hours for that tooth to work free.

Anyway, any further insight would be great...

Chris........

 

[Denise K]

You need to identify the drive and engine to us.

If it's an MC1, then there is another underlying problem the upper gears suffered from. The later driveshaft housing gears were cut differently (stronger) and that problem went away (mostly)..

Chris...

Ok, that's a Gen II drive (I was using the phone earlier and don't bother even looking at pictures of the phone )...

That's also a cracked tooth that's come away, unlikely to be lack of oil. Lack of oil overheats the gears, and they melt, literally!

So, what caused the crack? Did you, sometime in the last (about) 50 engine hours have an instance where the engine stalled due to rope fouling the propeller, or a sandbar strike, or something like that? Something that would have caused the engine to stall while the prop was loaded. The last thing any engine does as it stops is to 'kick-back'. When the prop's loaded when the engine kicks back, the back side of the gear teeth get a hard hit, an it cracks the tooth root, and it takes anything up to 50 hours for that tooth to work free.

Anyway, any further insight would be great...

Chris........

Apologies, still trying to learn all this (and intended to add the outdrive details to the original post).
You're correct, it is a Alpha, Gen 2, 1.62 gear ratio (if that matters)
Motor is a Mercruiser 5.0L, 220hp (let me know if further details on that are helpful), and it's all attached to a 2006 Sea Ray Sunsport, (that I can't stand the thought of it being down this year).
We had spent the week houseboating at Dale Hollow when this happened, the relevant history might include:
1) Had just recently switched (that trip) to a stainless steel prop to facilitate better hole shots for skiing (can get the differences in specs btwn that and the aluminum prop it had been running if relevant)
2) Had just briefly pulled my brother slalom for awhile shortly before this (good skier but big guy = 6'7'', ~300lbs), boat had never seen that kind of load before.
Other than that, nothing got stuck in prop, didn't hit anything that we know of (seems like we would've felt/heard something), nothing else weird - seemed to be running really well.
The year before, when I was still learning to launch/load by myself, I *may have* left the outdrive down as I pulled it out one day - definitely took some life off the outdrive, but that was well over 50 hours prior. Appreciate your insight on any of this!

 

[Denise K]

Most common cause of self destruction is low gear oil. Was that changed/checked? I'm assuming that you have a 1986 alpha one like me. But yeah, sometimes things fail, especially after 36 years.


The engine should be aligned whenever the outdrive is removed. Misalignment will usually trash the coupler, but could cause vibration. U-joints/gimbal bearing are the other usual suspects. Assuming u-joints are new, did the gimbal get checked? Was any water in the bellows?

I believe gear oil is checked/topped off every year when winterized, but will check on that. This is on a 2006 Sea Ray, so "only" 16 yrs new ;-)
Sounds like we definitely need to align the engine (or have it done), any thoughts on if the average mechanic could accomplish this easily enough? I need to confirm whether U-joints were replaced and state of the gimbal and bellows. Memory's a little fuzzy on those details, "fixed" it last year. Thanks for the pointers and will follow-up!!