Bravo 3 overheating gear failure

[RobJH]

I have a 2016 MerCruiser with a Bravo 3 leg all fitted new in 2016 to a 28ft Aluminium mono hull vessel. It is serviced every 100 hours by MerCruiser dealer. Since the MerCruiser was fitted the sterndive oil has been burnt black with the smell of burning. Just prior to the service about 80 hours the forward gears do not engage for up to 5 seconds. This was reported to the dealer. They change the oil and fix the gear/clutch problem.
After many services and the same problems they fitted a spray unit to the leg, but this "we fit them to all stern drives" cavitated so badly the vessel could not get to 10 knots. They removed that one and told me Mercury are designing a new spray unit. Another 100 hours to make it 400 they change the burnt oil, fix the cone clutch and fit the spray unit. At 450 hours I am travelling for 1 hour at 2800 revs at 19 knots and a very loud noise happens in the stern. I get it back to the mechanics and they discover the top box gears have broken {split} with signs of pieces of gear, bits of the case hardening chiped away and wear on the gears.
My question is this: I have read about the high temperatures the sterndrives can get to, 280 F so having the oil running at that temperature and then coolling down countless times for nearly 500 hours will this do damage to the top box, gears and bearings.

 

[alldodge]

The B3 drive is known to run hotter then any other drive. When the oil gets high the lubrication starts breaking down and can brake things, One of the things that are part of the X and XR drives are the top finned cap.



Not sure but do think this style cap will fit on all the newer swept back drives.

they fitted a spray unit to the leg, but this "we fit them to all stern drives" cavitated so badly the vessel could not get to 10 knots.

Sounds like your guys don't really know how to install the drive shower. There are 2 basic types, ones which have a hole drilled in the Cav plate, and the other is made by Simrek which is no drill.

The drill type has to have the hole drilled at the rear edge of the plate and the most important thing is it much be on the "down turn" side of the prop. If its installed on the up turn side it will suck in air and ventilate the prop.

The Simrek is a stainless steel tube that surrounds the drive and splashes water on it

 

[RobJH]

Hi and thank you for the reply. The shower unit was supplied by Mercury, the guys were told this is the shower unit Mercury use on all vessels over 600hp. That had to be a lie as the legs are the same and the design on the shower unit could only cause cavitation. The Mechanics told mercury that before they fitted it, but Mercury insisted. That is not the problem, it is the 450 hours of the leg running exceptionally hot before they fitted the correct spray unit, I am trying to find out if the constant high and low temperature can in anyway cause the gears to fail, which mine did at a cost of $10K with no explanation of why the gear split

 

[scoflaw]

What probably killed it was oil failure from the heat. Merc's racing oil is better than their high performance. I would run that in your new drive and change it more often.

 

[alldodge]

The B3 drive has maybe twice the amount of heat generated as the B1 or B2. With the lube getting black you need a shower of some type. The lube overheating will create more heat and the next thing to happen is gears break. The heavier the boat the more heat. There is no cooling system that can be added other then a shower. Showers can come from the exhaust cooling water or attached showers.

This is the Simrek type, same as I have on my B3



This is probably the type which caused your cavitation. This one is installed incorrectly because the tube is on the up turn of the prop



High powered boats with surface drive props use tubes attached to the top of the plate to suck air in and ventilate prop intentionally. The reason is to get the prop to spin faster so rpms increase. I can get into this further but just explaining what happens when tubes are placed in the wrong area.



Yours being a B3, if the drive type is installed it needs to be placed at the end of the last prop on the down side

 

[alldodge]

What probably killed it was oil failure from the heat. Merc's racing oil is better than their high performance. I would run that in your new drive and change it more often.

What racing motor oil?
If that is the case then no, I do not agree

 

[harringtondav]

I've used NEO synthetic gear oil for 21/22 years in my Alpha ll . I can still see the machining marks in my spiral bevel gear contact faces. Call them with your application. It's not snake oil. And my seals hold up just fine.

 

[RobJH]

Thank you ll for your input and I am now starting to believe the failure of the gears was due to constant overheating of the oil. I am hoping a metalurgist will be able to test the gears and give me the exact reason as to why the whole gear split.

 

[harringtondav]

Gears have two main failure modes: Tooth breakage from excess bending forces. In a marine drive this normally means the prop took a helluva whollop. The other is compressive failure which normally starts from pitting on the contact surfaces. Overloading can cause this. Also lack of lubrication (or good lubrication) can cause this failure. Once pitting starts, it goes downhill fast. The pitting can propagate cracks, and then breakage.

Also, if the spiral bevel gears were not set dead nuts to the shimming tool settings, all of the above can occur. The shimming achieves the factory matching of the gear set for cone point match and backlash. I believe this is the most critical step in out drive rebuilding, followed by correct bearing preload setting. Without these, a gear set won't last long.

 

[HT32BSX115]

I have a 2016 MerCruiser with a Bravo 3 leg all fitted new in 2016 to a 28ft Aluminium mono hull vessel. It is serviced every 100 hours by MerCruiser dealer. Since the MerCruiser was fitted the sterndive oil has been burnt black with the smell of burning. .

Can you tell us what engine you have in front of this Bravo III? Also, how heavy is your boat (in lbs)?

I've been running my Bravo III for over 12 years. Even after many hard long runs, the drive never gets more than slightly warm to the touch. If yours gets so hot as to damage synthetic oil, after a hard run it should cause the water to boil around it when you stop!

It's beginning to sound like your drive was defective from the start.

 

[scoflaw]

 

[HT32BSX115]

The OP's problem not an oil problem.......

 

[scoflaw]

The OP's problem not an oil problem.......

Disagree, I've had a couple of B'3's that turned the oil black in a 100 hours.. Better oil, and more frequent changes and a drive shower helped. This merc racing oil will hold up to extreme conditions better than that run of the mill "high performance".stuff.

 

[alldodge]

The Racing label is new, and since high performance changed from 85W-90 to straight 90W, appears just another marketing ploy.

Racing 85W-90
Extreme Performance 85W-90
High Performance 90W
Premium 80W-90

There are also different labels depending on if its old or new, and Mercury or Quicksilver. Folks with a lot of power (much more then were talking about) on OSO use various Merc products and also Amsoil extreme lube.

I also believe this was drive issue, with possible incorrect preload or something else inside which caused the increase heat. With normal use it should not have gotten that hot even without a drive shower.

 

[harringtondav]

I also believe this was drive issue, with possible incorrect preload or something else inside which caused the increase heat. With normal use it should not have gotten that hot even without a drive shower.

I'm thinking the same. Achieving the correct shimming and preloads is a time consuming pain, and some shops don't bother. "Heck, Merc makes those parts perfect same", and throws it back together with whatever shims came out.

Not knowing the history of your B3, (new, used?), I'd have a heart to heart chat with your service manager on this. If he twitches, fidgits, or mentions "perfect parts", I'd move on.

 

[scoflaw]

So I buy a new 280 Sea Ray with twin B3's. Oil is black on both drives at the 100 hour change.
Soo do I tell my dealer that both my drives were assembled incorrectly ? I chose not to, ran better oil with showers..Sold it with 700 hours on the clock

 

[alldodge]

Repeating the same comment 4 times doesn't make it anymore true then another mentioning a comment only once.

 

[scoflaw]

N you dis agreeing 3 times doesn't make you right either...o wise one. Just talkin real live experience here.

 

[HT32BSX115]

The Racing label is new, and since high performance changed from 85W-90 to straight 90W, appears just another marketing ploy.

Yup......And since there's still no NMMA standard specification for "Marine" gear lubricant, it'll just be another hypoid gear lube with a fancy name that meets ASTM, SAE and API standards for gear lubricant.

 

[RobJH]

Bravo 3 xr overheating from new

I did a post on this a while ago and cannot find it, but desperate to find an answer.
Motor and leg new. Mercruiser Diesel 320hp with Bravo 3xr leg.
Leg is serviced every 100 hours.
at 80 hours clutch slips, they fix it when doing the service.
The oil is burnt. This went on for 400 hours.
At 450 hours Mercury tell the dealer it needs a spray unit, they fit the mercury supplied unit and it cavitates.
they remove it and Mercury tell them they have to design a new on.
at around 480 hours the main top box gear break in two, no teeth damaged just the whole gear splits.
Questions
Do Mercury recommend the fitting of a spray unit on all Bravo legs.?
Do Bravo legs overheat?
would the heating of the oil which burns it badly cause something to fail in the top box, something like the case hardening break free and go through the gears?
Is this overheating of the oil in the Bravo 3 leg an inherent problem?
Does Mercury know about this problem.