Coupler Blew Up Today - Why?

[gamarines2]

I was taking my boat out for the winter today, and had it in wide open throttle when bang, no more forward motion, engine still running great (but then overheating), and burnt rubber smoke in the bilge. Smoked my coupler no doubt, but what would be the normal cause for this? Did my outdrive seize?

I had been taking on water all summer (about 5 gallons a week), figured I could get through summer and check it out when I pull it out in the fall.......big mistake, now the engine's gotta come out.

What should I inspect first?

Mercruiser 350 Mag, Alpha 1

[Don S]

Coupler Blew Up Today - Why?

I had been taking on water all summer (about 5 gallons a week), figured I could get through summer and check it out when I pull it out in the fall.......big mistake, now the engine's gotta come out.

There's your answer. Pull the drive, and check everything. Hard to say exactly what the problem is without actually checking things. We could guess, but you still have to check things to find out who wins the guessing game.

[dubs283]

my guess??

lack of maintenance - not pulling the drive at least every other season and properly greasing the coupler/driveshaft splines

best to pull the drive EVERY season end and do the proper maintenance

[gamarines2]

For the record, I personally pull the drive off every year.

[Bluestream]

my guess??

lack of maintenance - not pulling the drive at least every other season and properly greasing the coupler/driveshaft splines

best to pull the drive EVERY season end and do the proper maintenance

I don't think not greasing the coupler will cause it to fail. Engine has come out of alignment due due settling of the motor mounts, or rotten stringers/transom in the boat. This is what has likely caused the coupler to fail.

Were you checking the alignment each year when you removed the drive?

[bifflefan]

my guess??

lack of maintenance - not pulling the drive at least every other season and properly greasing the coupler/driveshaft splines

best to pull the drive EVERY season end and do the proper maintenance

With the ability to leap to an incorrect conclusion like that, you should be a superhero or an athlete of some kind.

For the record, I personally pull the drive off every year.

Without sounding to obvious, its could be a few things that cause it, not the least of which is, somethimes things just break.
As already stated, you need to pull the drive and engine and check it all out to see what the cause was. Also, amke sure you look at everything, even after you find what you think is the cause, you nay find more than one thing is in need of repair. Do a little CSI on it.

[Alpheus]

I don't think not greasing the coupler will cause it to fail.

Wanna bet?

What do you think will happen if a gimbal bearing over heats and freezes up?

Tell ya what, don't grease yours and leave it in the water with a leak and get back to us.

How and why is water getting in your boat?

Could it be the drive shaft bellows?

The damage is done and the culprit is:

I had been taking on water all summer (about 5 gallons a week), figured I could get through summer and check it out when I pull it out in the fall.

I think old Ben Franklin said it right back in the day.

An Ounce of Prevention is Worth a Pound of Cure

He must have been a boat owner....

[Don S]

There are two ways a coupler can fail, and yes, one of them is from lack of lubrication.
This picture from a Mercruiser training manual shows the 2 types of failure.
I added the blue text to the pictures.

[dubs283]

With the ability to leap to an incorrect conclusion like that, you should be a superhero or an athlete of some kind

when you pull upwards of a hundred drives a season like myself, it becomes quite obvious that a lack of lubrication is quite often the cause of coupler failures

rarely does one find a severely misaligned engine, it does happen, but most often the worn couplers i see are bone dry and the splines are half gone

the concluision i came to is based on information provided by the original poster and my personal experience - without being there with the original poster, that is the best i, or anybody else here can do

[Lou C]

Could be a combination of things, won't be able to tell till you get it apart, to see if it looks like either one of Don's pix there...
the taking on water part makes me suspicious of a rotted transom, and possible flexing of the transom mount...course it'd have to pretty bad for it to flex that much...

the other thing I can say is that people ask all the time...do I have to pull the drive each season...all I can say is what I've seen...I put a good coat of OMC triple guard grease on mine when I install it in the spring...when I remove it...it's still there...but I would not want to go a whole nother season, without fresh grease on the splines...and the splines on this 22 year old drive look like new...plus pulling the drive lets you see if you have water in the bellows....a gimble starting to get rough or ujoints starting to get loose...it's necessary despite all the stories "well I never took it off and never a problem"...YET....

[zbnutcase]

With steel shaft splines running on aluminum coupler splines, a lack of lube most certainly will cause failure. And if by chance your drive did lock up, it didn't cause the coupler failure, it merely finished it off.

[Haut Medoc]

Check the alignment before you pull the engine out, burnt rubber smell is likely option #2 & is generally caused by poor alignment.....
If it is, you will need to determine what is causing it.....
It generally doesn't happen over night......

[HT32BSX115]

Check the alignment before you pull the engine out, burnt rubber smell is likely option #2 & is generally caused by poor alignment.....
If it is, you will need to determine what is causing it.....
It generally doesn't happen over night......

If the rubber "donut" failed (spun), you probably wouldn't get a very good "alignment check" anyway would you?......... checking it on a "bad" coupler?

There's a third way the splines fail too..... My last boat went 39 years before the aluminum inner splines failed.....I don't think lubrication would have helped any more than it did! It just flat wore out!

[gamarines2]

I pulled the drive today (like I do every year). There was a good bit of clean gear lube in the drive shaft bellows. Enough that about half quart got dumped on my driveway. Water was not present in the gear oil or the bellows, but there was water in the exhaust bellows (which I believe is normal).

I sorta expected to find a couple of things. A seized gimbal bearing, an over-torquing on the drive shaft splines, or a seized out-drive, none of which were true. The gimbal moved smoothly and easily (and not dry), the splines were straight, and I could move the propeller shaft in both forward and reverse by manually turning (with just my hands) the drive shaft.

I haven't stuck the alignment tool in there, but will later. Could a 20 year old coupler just go? Seems there'd be some warning signs.

The water being taken on also remains a mystery. I sorta had it set in my mind yesterday that the driveshaft bellows could have caused all of this, but it is not proving true.

puzzled!!

[Bt Doctur]

"Enough that about half quart got dumped on my driveway".

Considering it holds a quart and a half and you were down a 1/2 quart,remove the top cap and look for this.

[gamarines2]

Well, the gears all looked good. I'm gonna split that drive and take a look at the lower unit's drive shaft. There was some metal in the drive's gear oil, probably not from normal wear. Maybe a bearing got tore up in the gear housing?

Could running that engine at WOT have broken a motor mount, or is likely a bad stringer as someone else has suggested.

I don't suppose using my alignment tool will tell me much until I get that coupler replaced, huh?

[Lou C]

look for cracks in the 'glass around the motor mounts and cracks on the transom around the transom mount...when I started doing the R+R on the drive myself I bought an alignment tool and check it each time it comes off...this way you can see if it changed from the season before...

I went back and read your original post...you were taking on 5 GALLONS a week? that's a huge amount of water....do you keep the boat covered...I'm assuming it does not have a self bailing deck.....my boat sits on a mooring all season (does have both a cockpit and bow cover, auto bilge switch) and I don't think it pumped out that much water ALL SEASON...if you had it covered, and the driveshaft bellows was not leaking...then you could have had a big leak around the transom seal that could have rotted the wood in there.....

[gamarines2]

Hey everyone, I may be missing something here. Is there a way to grease the coupler other than greasing the drive shaft splines when it is installed. Because that's all I have ever done. Is there a grease fitting on the coupler itself?

[HT32BSX115]

Is there a grease fitting on the coupler itself?

some of the newer Alpha and Bravo couplers have zerks on them so you can grease it without pulling the drive.....

[Haut Medoc]

If the rubber "donut" failed (spun), you probably wouldn't get a very good "alignment check" anyway would you?......... checking it on a "bad" coupler?

There's a third way the splines fail too..... My last boat went 39 years before the aluminum inner splines failed.....I don't think lubrication would have helped any more than it did! It just flat wore out!

What would be the harm in taking the one minute to do it?....
I think it would give an idea of how far it was off....
But, either way the engine will need to come out......

[Haut Medoc]

Hey everyone, I may be missing something here. Is there a way to grease the coupler other than greasing the drive shaft splines when it is installed. Because that's all I have ever done. Is there a grease fitting on the coupler itself?

Not on your model......

[HT32BSX115]

What would be the harm in taking the one minute to do it?....
I think it would give an idea of how far it was off....
But, either way the engine will need to come out......

Well,

yeah...there'd be no harm of course....

I would much more interested in the measurement with the new coupler though....

[Haut Medoc]

Well,

yeah...there'd be no harm of course....

I would much more interested in the measurement with the new coupler though....

Ultimately, yes.....

[Bluestream]

I am going to disagree with some of you on the coupler. The boat I have now was bought from the PO with a blown coupler. He was told $700-$900US to change it. I bought a used one for $35, and changed it in 2 hours work. The boat had the gimbal bearing changed 2 years ago, and the guy who did that job did not tighten the front motor mounts, and over time the adjusting nut turned down to the point where the engine was so far out of alignment the it took out the coupler. Picture attached shows the coupler and it does not look at all like the Merc bulletin for out of alignment. In fact the drive shaft splines still had grease on them.

You will not get much information if you try to check the alignment of a stripped out coupler, as there is too much play with the tool inserted.

I have seen boats come in with the shaft seized to the coupler to the point that the drive cannot come off without cutting the shaft from inside. Zero lubrication in there, but the coupler is still functional.

http://i1013.photobucket.com/albums/...t/cobra010.jpg

[Don S]

There are exceptions to every rule.