Why do gears chew up

[Mac3]

Hello, I while since I've posted, my 150FSXECR has been running fine for years. However...
Last outing I had no reverse , couldn't shift the selector. I got home and undid the sump plug and black tar spewed out at massive pressure.I dismantled the gearcase and reverse gear is fine, forward and the drive pinion are chewed out. There was no warning on previous outings of any problems. I replace the gear oil every 50 hours, about 35 hours since last one. I have ordered the parts to rebuild but my concern is why has this happened? Engine has 940 hours and about 200 hours ago I ran over a log and bent the prop and drive shaft. It was an insurance claim and to the best of my knowledge most parts were replaced at a dealers shop. It has been running fine during that 200 hours. Any thoughts?

 

[racerone]

On severe impact there is a chance that gear teeth suffer.-----May not be visible.---If gears are re-used than they suddenly fail.-----Also I believe there is a design flaw in that style of gearcase.----There have been many sudden unexplained failures !

 

[Faztbullet]

Also the housings warp over time..especially after a impact. If I have a customer with damaged gears or impact damage, I will only rebuild it if I check it with alignment tool. if case fails it gets a SEI unit.. i know dealers that rebuilt unit swithout checking alignment and 50-100 hours is all they will live before crapping replacement gears

 

[dingbat]

The oil should be changed every 100 hours or annually, whichever comes first to minimize the effects of moisture and lubricate decay.

Changing the oil every 50 hours tells us nothing about your change intervals. Some people put 50 hours on boat in a week. Some put in 15-20 hours a year.

Assuming the gears where not flawed to begin with, bearing failure is typically the result of misalignment, excessive end play, lubricate failure or a combination of all three.

Since that particular gear case has a history of mystery failures, I’m guessing a design flaw in the housing. Something misaligned, flexing, thermal issues or even an obstructed flow of lubricant into that area for one reason or another.

Close inspect of the failed components usually reveals the failure mode. Unless blatantly obvious, it can take some work to figure out the cause of the failure. A lot of which requires one to go back to the design table to short it out

 

[JustJason]

Improper assmbly, lack of good clean lube, impact damage will all cause gears to fail. However, gearing is simply a wear and tear item. Your engine will not last forever. A transmission will not last forever. And a set of gears in a lower unit will not last forever. Gearing is subject to shock loading as you use the boat. We live in society in which manufacturing is so good (IE with cars) that most people have forgot about simple wear and tear.

 

[racerone]

But the older V-4 and V-6 gear cases did not suffer from these mystery broken teeth !!

 

[Mac3]

Thanks for your comments, all helpful. So 50 hours is about a year and a half for me, you're saying annually then? Ok by me. I understand wear and tear. The no symptom thing worried me.

 

[Faztbullet]

But the older V-4 and V-6 gear cases did not suffer from these mystery broken teeth !!

That is before 'Hot Foots" higher mounting heights, more efficient props...now they hammer out the carrier and warp housing

 

[Mac3]

Ok I’m the kind of guy who will have a go at anything, I have the service manual and I can read... I’m going to service the gear case myself but I’m a long way from the nearest service centre it is unlikely I can get hold of the special tools I need can anyone give me the specs of the drive shaft spline socket and the pinion gear nut wrench, I’ll get them from my local tool shop. May I add i am a member of other forums (non outboard stuff) and they all profess to be experts but really aren’t,Iboats are nothing but helpful IMHO

 

[Faztbullet]

You cannot rebuild it without pinion tool..plus I would not attempt to repair it till housing was checked. If you have to buy the tools/parts to repair this will cost more than a replacement unit. SEI units have a 3 yr warranty...and I sell a ton of em.

 

[Mac3]

Thanks I appreciate your comments and prefer to buy a reco unit, however I’m in Australia, getting stuff interstate these days is hard enough, overseas I can’t imagine. I figure at worst result I haven’t made things different than they are now.

 

[Faztbullet]

Take or send housing to a dealer and have checked for alignment...