Broken Forward Gear? Cause?

[Kola16]

In the video, I go from neutral to forward, to neutral, to forward, to neutral and then rev it in neutral. Mercruiser 228 drive (1.5:1) with a drive shower installed and custom built 383 stroker at roughly 420 HP.

A couple of questions:
1. Does this sound like a broken tooth in the FWD drive gear in the lower unit? I was on plane at around 2800 RPMs. All of the sudden I heard a thunk like I hit a small piece of driftwood or something. I soon gave it a little more throttle to verify the engine and drive were fine, and it was immediately apparent that it didn't like that so I came off plane and put it into neutral. Everything seemed fine in neutral. Put it into FWD gear and I get this rhythmic clunk, clunk, clunk.... Reverse everything seems to work fine, no clunking. Revving in neutral seems to work just fine too. In forward, nope...

Drained the lower unit oil and got the full 1.5 quarts out. Didn't look milky or see any water, but there was definitely metal shavings in it. Didn't see any bigger pieces come out the little drain hole.

2. So the other question if it is the FWD gear, what do you think caused this? I am striking it up to being to high of horsepower and torque for the drive. I know the drive is only rated to 300 HP, which is why I put the drive shower on it and eased into planing. I probably only have 10-12 hours on this drive with this new engine. The drive as a whole probably has less than 500 hours on it even though it is a 1979. My dad bought it new off the lot then. The lower unit oil was always changed with synthetic Mercury oil every year while I have worked on it since 2017 or so. It sat since 1985 before that.

3. What should my next step be? Save up for a Bravo would be the best and what I want. Ultimately, Bravos are expensive and money is tight or else I would have done that already. I could rebuild the lower unit or buy a used one and bolt it right up and go boating. I don't want to do that though if you guys think that the high HP is what caused this and will just wreck the next one. I like reliability. I thought it was usually the upper's gears that failed over the lower's gears, but I don't know obviously haha.

 

[Scott06]

In the video, I go from neutral to forward, to neutral, to forward, to neutral and then rev it in neutral. Mercruiser 228 drive (1.5:1) with a drive shower installed and custom built 383 stroker at roughly 420 HP.


2. So the other question if it is the FWD gear, what do you think caused this? I am striking it up to being to high of horsepower and torque for the drive. I know the drive is only rated to 300 HP, which is why I put the drive shower on it and eased into planing. I probably only have 10-12 hours on this drive with this new engine. The drive as a whole probably has less than 500 hours on it even though it is a 1979. My dad bought it new off the lot then. The lower unit oil was always changed with synthetic Mercury oil every year while I have worked on it since 2017 or so. It sat since 1985 before that.

It could be the gears and or bearings had corrosion from sitting. Did i read that correct it was sitting from 1985 =>2017? When I bought my current boat in 2015, it was a 2004 that had only 37 hours on it. the lube that came out was pretty dark, assume it had never been changed. Had zero issue with drive no noise shifted fine.

Two years ago i got fishing line around the prop shaft seal, when I pulled the bearing carrier out I saw some corrosion inside, again never had any water in drive... upper bearing on top of drive had corrosion where the rollers were in place on the races, I assume from where it sat.

You know that boat not only in engine but also size of boat is getting on the edge of what an alpha /mc1 drive can handle. But the issue may be from sitting and have some issues with bearings more so than over stress. Only tearing down the drive can tell.

Certainly we have seen enough folks on here running 383 + alphas that I would not think 10-12 hours with this engine did the drive in.

 

[Kola16]

Yes my dad bought it new in 1979 and ran it till 1985. It then sat under tarps for 32 years till 2017 when I put it in the water. I took the top cap off the upper unit and I do see a little rusting in the top bearing and in the valleys of the upper gear. The little bearing on top spins freely. The upper gears were not missing any pieces. I didn't even think of corrosion, but that could definitely do it too.

But the issue may be from sitting and have some issues with bearings more so than over stress. Only tearing down the drive can tell.

That makes sense. I'll have to figure out how to tear the lower apart to see what I can find.