# Blown outboard prop shaft seal?



## GrahamO (Apr 4, 2012)

This is a weird one.

Tohatsu 6hp four stroke.

We stored it all winter on its (correct) side then transported it up to the boat in the back of our car, again on the correct side. We left it in the (hot) car most of the day and when I went to take it out I noticed a couple of drops of oil under the prop area. There were a couple more in the cart and it should have been enough to stop me then but I was not thinking. When I tipped the motor into the vertical position oil dripped out of the prop area at a pretty high rate. it slowed down then stopped when I laid it down again. The oil is discolored but not black and it is pretty thick so I am assuming it is transmission oil.

I am assuming I have a blown prop shaft seal, either due to excessive heating in the back of the car or due to side load on the prop during transport. So - as ever - questions:

1. Does this sound reasonable? If not - any other ideas?
2. If the seal has popped out can it be reseated?
3. How much is it likely to cost to get it fixed?

Thanks a lot,

Graham


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## MarkSailor (Oct 17, 2010)

I had the prop shaft fail on my mercury 6hp last year. They tend to fail from non-use. The seal is rubber, so the heat can also definitely contribute to failure. I don't remember what the labor to replace the seal was, because I had several other problems fixed at the same time.
I thought at first I would replace it myself, but the whole prop shaft had to be removed to get the old seal out, which was more than I was willing to tackle. The labor to remove the old seal and seat the new seal was definitely more than the part, so if you are going to do the work or pay for it, I'd replace the seal, not just re-seat it.


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## ScottyG24 (May 8, 2012)

You probably know this already but when you store your outboard for the winter or any period that is might be in less than 32f remove the prop and make sure (by tilting it) that all the residual water gets out of the torpedo/prop shaft area as ice can damage the seal. i doubt your transportation method damaged it. Get the service manual for the engine wether you fix it or have it done by a shop so you know whats involved to R&R it. Good Luck


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## GrahamO (Apr 4, 2012)

I probably didn't..... I've never owned an outboard in a cold country before so improper storage may well be the issue - oh well. Didn't have this problem in Australia... (never had to store it). doesn't look like the sort of job I want to tackle so dealer it is.



ScottyG24 said:


> You probably know this already but when you store your outboard for the winter or any period that is might be in less than 32f remove the prop and make sure (by tilting it) that all the residual water gets out of the torpedo/prop shaft area as ice can damage the seal. i doubt your transportation method damaged it. Get the service manual for the engine wether you fix it or have it done by a shop so you know whats involved to R&R it. Good Luck


Thanks

Graham


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## tommays (Sep 9, 2008)

Was the unit serviced in the fall ? gear oil change 

If not it is the best time as any water would not sit in the gear case over the winter 

I would remove the upper gear oil plug to check the level and be sure is in fact gear oil as the four strokes are funny about motor oil when transported laying down

If it is the gearcase there are three seals 

Input shaft, output shaft and the shift shaft and if your going to pay someone might as well do it 100% and be done


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## GrahamO (Apr 4, 2012)

Afraid not - I'm more of an electronics guy. I really don't like engines..... It was stuck in the corner and forgotten for the winter. I did flush the cooling system and run the carb dry. I have been belatedly reading the user manual and I am appalled at how delicate these damned things are. Surly someone can design a more robust motor that does not need so much pampering...



tommays said:


> Was the unit serviced in the fall ? gear oil change
> 
> If not it is the best time as any water would not sit in the gear case over the winter
> 
> ...


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## tommays (Sep 9, 2008)

You have to change the oil once a year how hard is that 

The rest of the issues are silly E-10 stuff that affects everything


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## GrahamO (Apr 4, 2012)

You mean all this?

①Wash the engine exterior and flush the cooling water system thoroughly
with fresh water. Drain the water completely. Wipe off any surface water with an oily rag.
② Use a dry cloth to completely wipe off water and salt from the electrical components.
③ Drain all fuel from the fuel hoses, fuel pump, and carburetor, and clean these parts. Keep in mind that if gasoline is kept in the carbruretor (yes - this is the spelling in the manual) for a long time, gum and varnish will develop, causing the float valve to stick, restricting the fuel flow.
④ Remove the spark plugs and spray storage oil (available from an authorized dealer) into the combustion chamber through the spark plug holes while slowly turning the motor over using the recoil starter.
⑤ Change the engine oil.
⑥ Change the gear oil in the gear case.
⑦ Apply grease to the propeller shaft.
⑧ Apply grease to all sliding parts, joints, nuts, and bolts.
⑨ Stand the outboard motor up vertically in a dry place.

Perhaps I should have waited until after I retire to get a boat.....

Been a bad week for me and engines. I managed to kill my equally abused lawnmower by filling the air filter with engine oil (another wrong-side issue....).


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## dabnis (Jul 29, 2007)

Before you have it worked on suggest you drain the crankcase oil. If the oil leak is still there it is probably gear oil. If the leak stops, it is probably crankcase oil. Maybe first , just put it in its normal upright position and see if it continues to leak. Maybe either crankcase or gear case were overfilled prior to storing it on its side? Try the easy things before ripping it apart?

I have had many outboards over the years and never had a prop shaft seal fail. Winding up monofilament in the prop can "suck" it into the seal and damage it. Maybe running in very muddy or sandy water may wear it out quickly?

Paul T


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## Sea Dawg (Jun 26, 2012)

You need to remove the prop and prop bearing carrier. It's not hard, and you'll be pleased with the confidence that you get. Look at a picture on Boat.net for your motor and you'll see it's a simple piece of machinery. Here's how it likely looks. Drain the oil. Careful removal and observation with a few pictures from a digital camera and you'll have it back together in a day. Order your parts ahead of time... anything rubber. Don't lose track of any shims or the order they came out. Good luck. 2002 And Earlier MFS6A Tohatsu Outboard GEAR CASE (PROPELLER SHAFT) Diagram and Parts


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## GrahamO (Apr 4, 2012)

I'm afraid I got it into the shop before I read the last few posts.... Too busy to mess with it at the moment anyway but I fully agree with the 'learn to be self sufficient' philosophy - oh well. I

suspect I will end up paying for a new seal that I probably did not need. Mind you, that pales into insignificance compared with the cost of my poor choice of yards this winter. Learning about looking after a large boat can be a VERY expensive process....

Thanks as ever for the support and advice.

Graham


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## willyd (Feb 22, 2008)

Sea Dawg said:


> You need to remove the prop and prop bearing carrier. It's not hard, and you'll be pleased with the confidence that you get. Look at a picture on Boat.net for your motor and you'll see it's a simple piece of machinery. Here's how it likely looks. Drain the oil. Careful removal and observation with a few pictures from a digital camera and you'll have it back together in a day. Order your parts ahead of time... anything rubber. Don't lose track of any shims or the order they came out. Good luck. 2002 And Earlier MFS6A Tohatsu Outboard GEAR CASE (PROPELLER SHAFT) Diagram and Parts


Sea Dawg, how do you get parts 10-14 in the diagram off of the shaft? My manual seems to skip this part, saying they all just slip off the shaft. I assume I need to use a puller, but not sure what to do here. Any help would be appreciated.


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## Sea Dawg (Jun 26, 2012)

Place in forward gear. Drain gearcase oil. Spray Croil or PB Blaster in the gearcase where salt crust builds and holds carrier from sliding out. Make a J-hook pulling tool out of flatbar by grinding a notch on a bench grinder. Grab the other end with vice grips to give you something to hammer against. There's openings on the inside of the carrier you can hook onto for pulling. Move from side to side a little at a time. 10 11 12 13 14 will be coming out. Don't lose track of orientation of pc's 2 3 5 6 7 8 9. Take notes. Note seal 11 and bearing 13 orientation before removal as compared to your new ones. A wooden or teflon dowel will be used to knock them out or a flat screwdriver for the seal. The gear oil is either leaking along the shaft from the seal or oring 12 along the gear housing. The new seal needs a smooth surface to run on at the shaft. Strap lap the shaft with fine emory cloth. The oring needs a smooth surface in the gear housing. Hand smooth any rough areas, but don't remove too much metal. Marine grease running areas at assembly so these don't tear your new parts. Pay close attention that you don't leave out the shifting parts and as you slide it back together rotate shaft until you get the reverse gear and splines lined up and don't force it until it starts into the bearing. Alternate taps with a mallet on the carrier should get you there. Lastly, use marine anti seize on the bolts.


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## Sea Dawg (Jun 26, 2012)




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## willyd (Feb 22, 2008)

Thanks for all the help so far. I got it apart, removed the prop seal, replaced the O ring, greased things up, and got it back together last night, but I'm not sure I got the thrust bearing (part 17) down all the way on the shaft - the bevel gear can still move a bit, maybe 3/16", back and forth on the shaft.


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## Sea Dawg (Jun 26, 2012)

I can't see how pc 17 controls the bevel gear movement. I'm thinking maybe the bearing or seal didn't go all the way home. THey have an interference fit. To push the seal home protect it with a piece of hard wood and smack it nice and square to drive it home. Hoping by now you got it finished, but try that if not.


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