Here is a wallowed out berring, which also happens when run with old or bad oil, or worst yet, straight water due to a crack or faulty seal.  The 2nd picture shows what happens when a lot of water is left in the gearcase during winter.  The pressure of freezing water blew the prop shaft bearing carriage right out of the back of the housing!

Maintaining Your Propeller

The propeller is like your tires, it's where the rubber hits the road.  Make sure the blades are all very closely curved to each other (in other words, not out of alignment, bent).  The leading curve is the most important one, but the entire blade should be evaluated.  If you see any nicks on the blades, those should be removed using a metal file.  Shave it down to a smooth, tapered edge.  You can repaint the blade using a good automotive paint (for durability).  If you have any major chips or bends, you may need to replace it or have a marina try to fix it.  But these days, unless you're dealing with an $800.00 propeller (say, for big boats), it may make sense to go and buy a new one.  Most props aren't much more than $150.00.  If your prop is spinning and vibrating wrong due to bent blades, that can cause problems with your entire motor, specifically the gearcase, driveshaft, seals, and potentially the crankshaft and powerhead.

You should pull your prop every so often to make sure there isn't fishing line wrapped around it.  Even if you don't fish, check the propshaft for line.  If you don't, this stuff will wind around behind the prop in a matter of seconds and cut into your prop shaft seals, leading to water intrustion, and gearcase failure (quickly, too).  Put some grease on your prop shaft to make sure the prop doesn't get seized to the propshaft, which I see happen. 

The picture I have here is what I found on a motor where the gearcase had a bad seal.  The beginning of that repair process involves pulling the prop.  This is what I found.  It doesn't take long to figure out why the gearcase had a bad seal after seeing this. There was about 20 feet of line wrapped around this prop, and it was leader and regular line, along with 5 hooks.  Believe it or not, all of this was hidden out of sight and could not be seen with the prop on the gearcase.  Picture #2 is what happens if this is left for awhile, and the line heats up enough (yes, even under water) to melt.


Your prop nut (if equiped, newer motors have splined hubs, prop nut, and cotter pin) should be the correct one.  Often times the 'redneck fix' is to locktite a hardware store nut to the prop shaft.  WRONG.  It usually takes a blow torch and a long breaker bar to pull the nut off, and potentially drilling out the cotter pin orifice or even replacing the prop shaft all together if damaged.  Taking shortcuts may seem sensible in the interim, but causes bigger problems down the road and more repair bills.  (picture 2)



How to Shift Correctly

This is a conversation I have with every operator that I sell a motor to, or just generally deal with.  The #1 reason why your gearcase fails is incorrect shifting.  If you watch the video on this page, it explains the problem more.  Here is a picture of a worn clutch dog.  You should here a 'clunk' when you shift, and do it as fast as possible, with the motor at the lowest RPM you can make it go (low idle, for instance).

When the clutch dog is worn, the motor may jump out of gear, or not stay in gear at all.  This may also happen due to a worn forward gear, or if your shift linkages are not calibrated properly (which happens a lot with DIY-ers who service their own impellers).  The first picture is of a good clutch dog.  Pictures 2-4 are bad (3 different ones...fairly common situation I run into in repairs).  Notice the leading edge is rounded off, where a good clutch has little to no wear on the leading edge.  Some wear is normal, and there is nothing you can do about stopping this.  They all go bad eventually and this is normal replacement item over time. 

Remember many of these things last decades before failure.  But if you're consistently shifting wrong, this will significantly accelerate this issue, and if you are using a motor with remote controls where your shift box is set up wrong, you can ruin your gearcase in a matter of a few days or weeks.  All the more reason to have things set up by a good mechanic.


If you don't shift correctly sometimes the shift cradle or lever can become damaged.   These are the least costliest parts to replace, but will cause the gearcase to jump out of gear at any range, even idle.  A collision with an object can cause this too.  Remember there are a lot of forces being generated by a working motor.  A sudden jolt to these parts get's transferred to something; there's really no way to predict what can happen.

The top row shows (left to right) 1) a worn lever, 2) what it looks like zoomed out, and 3) a pitted lever from a rotted out gearcase left to sit with water and no oil (failed seals, water gets in from condensation and the motor sitting for years).

The bottom row shows the cradle that is damaged (likely a collision) and zoomed out what it looks like.  In a perfect world, either of these situations would be the source of a failed gearcase.  In reality, it's almost always the clutch dog or forward gear.  The clutch dog is between $70-200, the forward gear generally is $500.00+.  Not because it costs more to make, but because it is a common wear item that manufacturers can kill us all on.


Here is another pic of a more modern shifter yoke where the hook that grabs the cradle which actuate a clutch dog has broken off.  The motor was stuck in forward gear; pulling the gearcase apart revealed a simple problem.  Replace this part and voila, the gearcase is restored to proper working order.



Stuck Driveshafts

Here we have a situation where you go to remove the gearcase for water pump service, only to find the gearcase won't come out of the motor after having taken all the gearcase fasteners out, and disconnecting the appropriate shift linkages.  This generally happens because the last person who did this forgot to put grease on the driveshaft splines and/or put an O-ring at the top of the driveshaft if the motor calls for it (some don't).  Again - this is amateur hour at it's finest.

Now your driveshaft has seized up into the crankshaft of the motor.  The next option is to force the gearcase off, causing the driveshaft to pull up through the impeller housing and breaking a small portion of the impeller housing due to the impeller key forcing it's way up through the impeller housing.  On newer motors where the housing has a water seal, this will require a full replacement of the imeller housing.  But  this is the least of your problems.  Now you have to figure out how to get the driveshaft out of the crank, if even possible.  I have had about a 50% success rate at doing this.  If you can't get the driveshaft out, whatever way you try, then you have to do a full teardown of the motor and replace the crank.  Lots of headaches.

For the average person, you might as well accept the fact that you will need to buy a new motor at this point.  Cranks cost a ton of money, and there will be many, many hours of labor involved and other parts (i.e. gasket, fastners, etc) that now need replacement.  The reason is because when you pull the motor apart completely, chances are the gaskets that hold it together will not be reusable. 

You *might* get lucky by hanging the motor upside down from a vice and pouring a lot of penetrating oil down the driveshaft to the bottom of the powerhead.  From here you put a large piece of thick flat stock metal across either the exhaust housing or the bottom of the powerhead, then strike it with a 8lb sledge.  This works sometimes and when done correctly will not damage the motor (you may damage the lower crank seal, still requiring a full teardown of the motor to replace the seal).  Depending on the motor, this may not be possible, particularly for very small or very large motors.  Either you're going to break the exhaust housing or powerhead striking it, or the motor is too big to hang upside-down to attempt this process. 

Just another reason to leave repairs to someone who knows what they're doing.

I had a customer donate a 15hp motor one time (this happens frequently with people who decide to take on jobs well outside of their knowledge base, usually destroying the motor, and donating it when they buy a replacement).  The motor showed up with the driveshaft cut in half.  Keep in mind this is 3/4" stainless steel rod.  (picture 1 below)

He went on to explain that the motor wouldn't shift, and when he went to pull the gearcase off the driveshaft was stuck in the crank.  Rather than follow the procedure he should have, he made a bad problem catastrophic by cutting the driveshaft in half.  I was able to remove the driveshaft after pulling the powerhead and using the process I described previously.

Water Relief Holes and Why They're Important

Continuing on from the previous title (stuck driveshafts) the gearcase was a different story.  The reason why the shifter wasn't working is because apparently he had used the motor in shallow, sandy waters quite a bit.  Most gearcases have water relief holes to allow water to drain out of the various passages and cupped internal sections.  This helps prevent filty build up, carbon and exhaust ooze to wash away, and otherwise discourage burst housings due to water freezing when left out to cold climates (picture 2).


When I pulled the 'nub' of the driveshaft from the crank, it revealed that the crank orifice was also full of hard packed sand, with no evidence of having grease.  This is why the driveshaft was stuck.  I also had to use a pick, compressed air, and repeatedly driving the driveshaft 'nub' into the splines of the crank orifice to essentially purge all contaminants until it could be installed and removed normally.  I actually would up using the removal trick 8 times in a row, each time getting easier and easier, until eventually the driveshaft could be removed with just the force of my arm pulling on it (normal).  Adding plenty of grease and making sure both the female and male end splines where clean brought things back to normal.

Once again, poor servicework by either a low-skilled mechanic or unknowing operator lead to needless headaches and problems for this motor.  Fortunately, I was able to restore it to proper working condition and it lives on to put smiles on it's new owners face.  This is a happy ending, but for everytime this has worked, I can think of at least the same number if not more times where I have to replace the crank and driveshaft completely to restore the motor, or just send it to the scrap yard.  All due to laziness/incompetency in carrying out a repair properly.

Here is a picture of what happens when you let this stuff build up with salt and sand, then let it freeze.  This is from another 15hp gearcase, and it actually blew out completely.  Let's just say the first words out of my mouth when I saw this weren't exactly "I have to take a picture of this one."  You can fill in the blank.



Stuck/Frozen Shifters



Before you get worked up, make sure you don't have your throttle all the way up to the point where the low idle lockout isn't engaged.   Many motors post 1960 have a cam/mechanism which prevents a manual starter from working when you are throttled up high.  The reason for this is if you accidentally turn off the motor and are in forward gear, then try to start the engine up, you could easily fall out of the boat (or a passenger), then the motor makes a hard port side turn, circles around, and you get run over by the propeller and die.  This happens every year in every state due to broken remote steering cables (make sure you check them regularly). 

These basic safety features also prevent you from shifting out of forward gear into neutral or reverse when at wide open throttle.  What happens when you slam your brakes on in your car without wearing a safety belt?  You go out the windshield.  Well in a boat, you fly out of the boat (or a passenger), then get run over by your own boat, and die.  Again, boating isn't for everyone.  You have to have at least >some< brain activity to be a good skipper.