Bravo 3, gear lube leak, Mecruiser 350 Mag MPI,

[TheSub]

For the third time this season the oli level in the gear oil reservoir suddenly drops and it all ends up in the bellow. Twice I have had the radial seal on the yoke, in the lower unit, replaced by a mechanic but still it comes of after a few hours and causes the oil to enter the bellow. The mechanic is amazed and got no clue on how this might happened. He has replaced numerous of these seals and never come across this situation. The oil shows no sign of overheating end there is no overflow of oil in the engine room. There is no water in the oil.The engine is aligned and the other bearings are intact and in good condition.

Any ideas on what this is all about?
Thanks

 

[Bt Doctur]

had the radial seal on the yoke, in the lower unit,

The inputshaft seal is in the upper unit, that seal and yoke are the only way to have oil in the bellow

 

[TheSub]

I might have been using the wrong terminology. Sorry about that.
However it is the seal around the yoke that keeps coming of as if it has been pushed forward along the yoke shaft. It came off for the first time early this spring. The mechanic found yoke being slightly worn so he had it and the seal replaced. A few weeks later the oil level sunk again and an inspection found that the seal had come of partially. Leaking. A new seal were installed and extra attention were paid to it being perfectly installed. Still, it came of again less than ten engine hours later.
The mechanic is skilled and affiliated with a well know marine service establishment with god reputation.
The waters are far from tropical in terms of temperature and the engine has been running way below WOT. Rather at a speed, 23 knots 3800rpm. No heavy load.
I find it unlikely that the pressure in the gear oil could reach levels enough to displace the seal. In humble opinion any excess pressure would be released through the cap of the reservoir in the engine bay. Right?
Any ideas?

 

[Pocket Change]

The relief valve in the cap isn't working. It's not letting the pressure out. Had the same thing with my alpha 1. Kept blowing seals. I removed the valve from the cap and no more problems.

 

[Pete104]

The relief valve in the cap isn't working. It's not letting the pressure out. Had the same thing with my alpha 1. Kept blowing seals. I removed the valve from the cap and no more problems.

Or, a build up of sludge in the plumbing from bottle to drive not allowing pressure relief to the bottle. Possibly the bayonet fitting could be not cooperating some how.

He's done the new yoke. Did he replace the seal carrier? Can't say that is recommended on a reseal but you never said how old this thing is either!

 

[alldodge]

The mechanic found yoke being slightly worn so he had it and the seal replaced. A few weeks later the oil level sunk again and an inspection found that the seal had come of partially. Leaking. A new seal were installed and extra attention were paid to it being perfectly installed. Still, it came of again less than ten engine hours later.

Could use a drive serial number to see if there is any bulletins out about it, but my first guess is the bearings and/or races are worn. Think your dealing with someone which knows how to replace parts but does not know how to analyze what the issue is

 

[TheSub]

I?m thinking of Pocket Change idea of removing the pressure release valve in the reservoir cap.
Will I, by doing that, compromise any need for a slight increase of pressure that the lube system might need or does it not need any pressure, just enough lube oil?

 

[alldodge]

You will reduce the pressure in the drive but it will blow lube oil out the cap as the drive heats up. The one way check valve (air in nothing out, like hotel California) keeps the drive full and keeps air from making its way in

 

[Pocket Change]

When my drive was blowing seals two mechanics at two marinas told me to take the valve out of the cap. That was 6 years ago. Oil isn't blowing out of the cap because the valve is gone. I just stopped blowing seals. The level in the bottle is 2 inches below the cap. The level goes up maybe 1/2 inch when the oil is warm.