Bravo 3 overheating gear failure

RobJH

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Aug 18, 2018
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Thank you all for your very helpful posts.
Just a couple of questions.
Does Mercury know about Bravo 3 xr legs overheating problem.
Do all Bravo 3 legs overheat?
would the oil overheating cause the main top box gear to split in two?
Would the overheating cause case hardening to break away and go through the gears?
The Mercury dealer kept blaming the clutch for casing the oil to heat, should they have known about this from Mercury.?
 

alldodge

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The B3 drives do get hotter and always will. Them getting hot enough to break things in short amount of time would need to be analyzed. I don;t see this as just the drive but maybe how its being cooled. Being a diesel the rpms are lower at cruise and torque load high.

Not all overheat, but all do run hotter then B1 and B2. Those that do overheat may have other contributing factors that increase the heat. The drive needs a shower. Have you tried to contact Merc directly?

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

is incorrect, Merc now has a full synthetic gear lube and is labeled Racing. It is amber colored and is trying to get some of the offshore boats to come back. Many of them still use amsoil
 

RobJH

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I run my engine at 2800 rpm cruise speed. The first 100 hours had the clutch slipping, would not go into forward gear for at least 30 seconds from 60 hours, when the clutch was done they blamed the clutch slipping for the reason the oil was severely burnt, I had the clutch done every 100 hours and at 450 hours mercury finally said they need to fit a spray unit because they overheat, so Mercury knew they overheat but I was never told this. So for 450 hours this leg was running at 267 +F, Mercury claim it only overheats on 600hp motors or higher.
 

alldodge

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The clutch keeps coming up, but the clutch only slides up or down until gears mesh. Its not like a clutch on a car/truck where its not fully engaged.

The clutch does not slip, it either goes into gear or fails to go into gear. When it does not go into gear the prop does not turn and next to no heat is generated. When the clutch engages the prop turns and heat is generated.

I have single 530HP on my XR B3, pushing a 11K pound boat and it does fine. Every year I change the lube its the same color as it went in. There are others with offshore boats running higher HP and they run without issue.

I would like to see picks of the drive running at cruise to see how it sits.

Does the drive have a shower installed?
 

scoflaw

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Of course the clutch slips, that's its function. If no slippage was needed it would be gear on gear

That's why they wear and get replaced
 

scoflaw

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How does it slip?

Slips a small amount on every shift, that's why it shifts smoothly, unlike the dog clutch on an outboard. Same with Alpha's needing a shift interrupt. New clutch has sharp edges, they flatten when worn. The cup on the gear gets glazed from the slippage.
 

muc

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I run my engine at 2800 rpm cruise speed. The first 100 hours had the clutch slipping, would not go into forward gear for at least 30 seconds from 60 hours, when the clutch was done they blamed the clutch slipping for the reason the oil was severely burnt, I had the clutch done every 100 hours and at 450 hours mercury finally said they need to fit a spray unit because they overheat, so Mercury knew they overheat but I was never told this. So for 450 hours this leg was running at 267 +F, Mercury claim it only overheats on 600hp motors or higher.

Hi Rob,
The way I read this is that you have had 4 clutches replaced? How many times have the gear sets been replaced?

If you are looking for help keeping this from happening again. I can probably help based on over 30 years as a marine tech, the last 15 years as a MerCruiser Master Tech.

But if your looking for help trying to get MerCruiser to help out more $$$$ than they have. I won't be much help because the times Iv'e seen this problem. It has always been due to the drive being used in "severe duty" or operator / boat issues.
 

RobJH

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Hi and thank you for replying. The engine very rarely exceeds 2800 rpm and the mechanics put the computer on it to see if it had been abused and they said I was actually being a bit under what I could run the motor at.
The clutched were honed, reversed and replaced, but since the gears broke and the overheating partially solved {last service they said it was a little burnt, to me burnt is burnt :).
The gear that broke, split in two right through both sides of the whole gear, slight tooth wear, the whole gear was lifted away from the hub.
The spray unit fitted the first time caused cavatation, the second one has help reduce the heating to a point as the oil is still burnt. The spray units are Mercury designed and supplied {at my cost}
 

RobJH

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To the guys trying to help, I used the term slip because I will put the gear selector into forward and it will sit there for up to 30 seconds before engaging unless I rev and it will go in way too hard, in reverse it goes into gear immediately. As the oil burns it "slips" I am trying to find out if constant overheating at around 267 f will cause metal failure thus causing gear failure
 

RobJH

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the clutch does not engage for at least 30 seconds, which is why I used the term slipping, which it is then it engages. In reverse it engages within a second. The problem is not that, it is what I used as to what the mechanics thought was causing the oil to burn. I had the oil tested and the PQ Index was 3485 which is severe. So I am trying to find out if 450 hours of overheated oil to 267 deg F would do any damage to any metal within the gears housing.
 

RobJH

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Hi, the clutch does not engage for at least 30 seconds and that is what the mechanics were thinking was causing the oil to burn. I am not worried about that I am concerned that the oil heating up to over 267 deg F is causing metal fatigue or some damage to the metal within the top gear box.
 

alldodge

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will put the gear selector into forward and it will sit there for up to 30 seconds before engaging unless I rev and it will go in way too hard, in reverse it goes into gear immediately.

If this happens there is an issue with the clutch assembly

engine very rarely exceeds 2800 rpm

Don't know (or remember) what motor is in the boat but can the motor reach max WOT rpm?
 

muc

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Hi and thank you for replying. The engine very rarely exceeds 2800 rpm and the mechanics put the computer on it to see if it had been abused and they said I was actually being a bit under what I could run the motor at.
The clutched were honed, reversed and replaced, but since the gears broke and the overheating partially solved {last service they said it was a little burnt, to me burnt is burnt :).
The gear that broke, split in two right through both sides of the whole gear, slight tooth wear, the whole gear was lifted away from the hub.
The spray unit fitted the first time caused cavatation, the second one has help reduce the heating to a point as the oil is still burnt. The spray units are Mercury designed and supplied {at my cost**

“Honing” or reversing a clutch isn’t a recommended repair. Not sure what your dealership is doing.
I don’t think the overheating is what cracked the gear. It is more likely the delayed shift engagement is what caused it. That noise you hear when advancing the throttle before the clutch has engaged is the shock loading of the gears and bearings. It’s very hard on them and will result in breakage if not addressed ASAP.

If you post or PM me your drive serial number I can see what repairs have been authorized by MerCruiser and maybe make a recommendation on how to proceed.
 

RobJH

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it is a 320hp mercruiser and I can get it too the maximum revs. Since the shower no problems yet, it is still burning the oil slightly. Will the gears go in another 450 hours ? I believe the oil running at 267 + deg for 100 hours each time the oil is so damaged it has no lubricating ability and caused wear. Changing the oil every 100 hours did not fix the burning problem only replaced bad oil for good oil which burnt in the first run.
 

alldodge

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If you still have the receipts the serial number should be on the ticket. When the drive was bought new all the info should be on the receipt. Without a serial number there would be no record of warranty repairs

MUC will know best, but hope your using Merc full synthetic racing lube oil
 

muc

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but hope your using Merc full synthetic racing lube oil

This might be an application that could benefit by using better lube.

Better oils and lubes are ---- well ---- better. But not always worth the extra $$$$. Depending on why this drive is running so hot. Just make sure that your using a grade of oil that matches the requirements for your application. We are starting to see failures of VVT engines that the customer thought they should use a heavier weight oil in. Caused problems due to the small passages that feed the variable valve timing actuator.
 

scoflaw

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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.
















doubt it's getting burnt on the first run
 
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