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Author Topic:   Propeller: Removing and Changing

John W posted 07-27-2005 07:46 PM ET (US)
I plan to change the prop on my 1999 Johnson 150, but have never changed a prop before...I'll be taking off an aluminum 15x17 OMC prop & installing what I believe is an OMC "SST" 14-1/2x19 pitch prop. Are there any tricks to this? The instructions I've seen for changing a prop suggest a particular torque value when tightening the prop nut; I don't have torque wrenches, are they needed? Or can I simply tighten everything as tight as I reasonably can?
Advice appreciated. Thanks,
John
davej14 posted 07-27-2005 07:58 PM ET (US)
I would strongly recommend that you purchase a torque wrench and a socket that will fit your prop nut. while you are at it I would also get a socket that would fit your spark plugs. Shouldn't cost you over $40.
Apply a liberal amount of marine grade grease to the spline shaft before assembling the new prop.
jimh posted 07-27-2005 08:40 PM ET (US)
Changing the propeller is very simple, however there are some potential problems.
If the propeller has not been changed in a long time it is possible--perhaps very possible--that the propeller and the propeller shaft have formed a strong attraction for each other. You may have some difficulty removing the old propeller. It depends on how long the two dissimilar metals have been in contact, how long they've been in the water, and how much grease was applied to the propeller shaft before they were put together.
If the old propeller does not come off easily, you may have to persuade it to slide off. One method is to apply a little heat.
Assuming you get the old propeller off--which you probably will be able to do--changing propellers is very simple. Remove the thrust bearing and look it over for signs of a any damage. Grease and reinstall it. Grease the shaft and slide on the new propeller. Add the spacer washer and retaining nut. Tighten to about 60 ft-lbs, or as tight as you can with a plastic propeller wrench. Add the keeper nut. On an OMC this will be a special keeper nut. Then add the cotter pin. Use a stainless steel cotter pin of the proper size and length. Bend the ends over to retain the cotter pin.
The forces created by the propeller tend to push it onto the propeller shaft in forward gear. The nut is there to retain the propeller when you are in reverse. If you are going to lose a propeller, it will be when you hit reverse with heavy throttle.
I have changed the propeller on my OMC engine about 20 times this season. Sometimes I remove the propeller when the boat will be in storage for a while so the propeller won't get damage if the boat has to be jockeyed around at the storage yard--those guys have been known to back a boat up until they hear a crunch. I have a little kit of parts and tools to accomplish this. What you need:
--block of wood to wedge between propeller and anti-cavitation plate to jam propeller into a stop;
--wrench to fit propeller nut. On an OMC (and most others) this will be a 1-1/16th inch nut;
--extra stainless steel cotter pins. (I reuse them once or twice then discard.)
--needle-nose pliers to insert and bend cotter pin;
--OMC Triple-Guard grease of equivalent waterproof grease to grease shaft.
I actually do have a 1/2-inch socket and a torque wrench so I can set the propeller nut to the specified tightness, but I would guess about 95-percent of the people just use a plastic floating propeller nut wrench and heave on it as tight as they can. On a V6 OMC lower unit the specified torque on the propeller nut is 70-80 ft-lbs. (On a V4 the torque is 120 inch-lbs.)
Tom W Clark posted 07-27-2005 08:51 PM ET (US)
Oh! for the love of Pete. You don't need a torque wrench to change a prop.
Tighten the nut with a 1-1/16" socket on a 1/2" ratchet (or use a "prop wrench" as Jim describes) until it is snug. Advance the nut until the cotter pin hole in the nut aligns with the hole in the shaft (in the case of a OMC, Bombardier or Yamaha outboard) or until the tabs on the locker washer align with the nut (on a Mercury).
Put the boat in the water, run it and recheck the tightness of the nut the next time it is out of the water. Advance the nut 60 or 120 degrees if necessary and install a new cotter pin.
Chuck Tribolet posted 07-27-2005 09:05 PM ET (US)
V6: 70-80 foot pounds.
V4: 120 inch pounds = 10 foot pounds.
That does not compute. Get out the service manual. YEP,
that's what it says, and the metric equivalents agree, at
least by eyeball. Amazin. It must have something to do
with the V6 putting the cotter pin through that sheet metal
hat while the V4 puts the cotter pin through a slot in the
nut.

Chuck

Peter posted 07-28-2005 07:34 AM ET (US)
I'm with Tom on this ... a torque wrench isn't necessary. In all the many, many years I've been boating with outboard motors, changing removing and reinstalling propellers on motors from 4 HP up to 225 HP of various brands, I've never used a torque wrench to tighten a prop nut and I haven't lost a prop yet.
jimh posted 07-28-2005 09:07 AM ET (US)
OK, make that 99-percent of the time people don't use a torque wrench.
I bought the 1-1/16-inch socket because my floating plastic wrench was getting a little sloppy.
The suggestion to re-check the tightness of the propeller nut after running the boat is a very good one.
bsmotril posted 07-28-2005 10:11 AM ET (US)
If the prop is snug on the shaft, this method will sometimes help break it loose as long as the corrosion is not very bad.
1) Put the flush muffs on the motor, hook up the hose, and make sure the hose is clear of the prop. Make sure the motor is vertical.
2) Put the prop nut and washers back on until they are finger tight snug to the prop, then back it off 1/2 turn.
3) Start the motor up and run it at idle speed in neutral.
4) Double checking the prop area is clear, and you have water flow out the aspirator first, shift the motor into forward, gear, then to neutral, pausing a few seconds, then into reverse. Repeat this a few times.
5) Shut the motor down, and check the prop. If it is not loose now, you'll have to resort to the other methods mentioned here. This works best on heavy stainless steel props where their mass and inertia helps to break loose the corrosion between the prop hub and prop shaft. BillS
Matthew posted 07-28-2005 11:28 AM ET (US)
Check to make sure that the thrust washer hasn't stuck to the engine side of the old propeller when removed. You will think that the new prop went on "just as the old one came off", but you will be missing an important component.
John W posted 08-01-2005 11:06 PM ET (US)
Thanks for all the replies & advice. I'll be changing the prop this weekend & will follow the tips here.
Thanks again,
John
kamie posted 08-02-2005 02:46 PM ET (US)
I suggest the metal prop wrench, the plastic ones strip if you change props a lot or your got a prop nut on really tight. The other handy thing is to take a length of 2X4 and drill 3/4 inch holes in each end. That way you can put a spare dock line through it and tie it off to the stern cleats. Very handy if you ever need to lean over and remove the prop from inside the boat. You can tilt up the engine, thread the board between the prop and the cavitation plate, tie it off and still have two hands, one to loosen the prop and one to hang on so you don't fall out.
kamie.homeip.net/prwc/Evenstar/Misc_Evenstar/misc_evenstar_7.html
As for torque wrenches, that is way over kill. I have yet to loose a prop because it slipped off. I have lost a metal prop wrench, so keep an eye on those.

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Author	Topic: Propeller: Removing and Changing
John W	posted 07-27-2005 07:46 PM ET (US) I plan to change the prop on my 1999 Johnson 150, but have never changed a prop before...I'll be taking off an aluminum 15x17 OMC prop & installing what I believe is an OMC "SST" 14-1/2x19 pitch prop. Are there any tricks to this? The instructions I've seen for changing a prop suggest a particular torque value when tightening the prop nut; I don't have torque wrenches, are they needed? Or can I simply tighten everything as tight as I reasonably can? Advice appreciated. Thanks, John
davej14	posted 07-27-2005 07:58 PM ET (US) I would strongly recommend that you purchase a torque wrench and a socket that will fit your prop nut. while you are at it I would also get a socket that would fit your spark plugs. Shouldn't cost you over $40. Apply a liberal amount of marine grade grease to the spline shaft before assembling the new prop.
jimh	posted 07-27-2005 08:40 PM ET (US) Changing the propeller is very simple, however there are some potential problems. If the propeller has not been changed in a long time it is possible--perhaps very possible--that the propeller and the propeller shaft have formed a strong attraction for each other. You may have some difficulty removing the old propeller. It depends on how long the two dissimilar metals have been in contact, how long they've been in the water, and how much grease was applied to the propeller shaft before they were put together. If the old propeller does not come off easily, you may have to persuade it to slide off. One method is to apply a little heat. Assuming you get the old propeller off--which you probably will be able to do--changing propellers is very simple. Remove the thrust bearing and look it over for signs of a any damage. Grease and reinstall it. Grease the shaft and slide on the new propeller. Add the spacer washer and retaining nut. Tighten to about 60 ft-lbs, or as tight as you can with a plastic propeller wrench. Add the keeper nut. On an OMC this will be a special keeper nut. Then add the cotter pin. Use a stainless steel cotter pin of the proper size and length. Bend the ends over to retain the cotter pin. The forces created by the propeller tend to push it onto the propeller shaft in forward gear. The nut is there to retain the propeller when you are in reverse. If you are going to lose a propeller, it will be when you hit reverse with heavy throttle. I have changed the propeller on my OMC engine about 20 times this season. Sometimes I remove the propeller when the boat will be in storage for a while so the propeller won't get damage if the boat has to be jockeyed around at the storage yard--those guys have been known to back a boat up until they hear a crunch. I have a little kit of parts and tools to accomplish this. What you need: --block of wood to wedge between propeller and anti-cavitation plate to jam propeller into a stop; --wrench to fit propeller nut. On an OMC (and most others) this will be a 1-1/16th inch nut; --extra stainless steel cotter pins. (I reuse them once or twice then discard.) --needle-nose pliers to insert and bend cotter pin; --OMC Triple-Guard grease of equivalent waterproof grease to grease shaft. I actually do have a 1/2-inch socket and a torque wrench so I can set the propeller nut to the specified tightness, but I would guess about 95-percent of the people just use a plastic floating propeller nut wrench and heave on it as tight as they can. On a V6 OMC lower unit the specified torque on the propeller nut is 70-80 ft-lbs. (On a V4 the torque is 120 inch-lbs.)
Tom W Clark	posted 07-27-2005 08:51 PM ET (US) Oh! for the love of Pete. You don't need a torque wrench to change a prop. Tighten the nut with a 1-1/16" socket on a 1/2" ratchet (or use a "prop wrench" as Jim describes) until it is snug. Advance the nut until the cotter pin hole in the nut aligns with the hole in the shaft (in the case of a OMC, Bombardier or Yamaha outboard) or until the tabs on the locker washer align with the nut (on a Mercury). Put the boat in the water, run it and recheck the tightness of the nut the next time it is out of the water. Advance the nut 60 or 120 degrees if necessary and install a new cotter pin.
Chuck Tribolet	posted 07-27-2005 09:05 PM ET (US) V6: 70-80 foot pounds. V4: 120 inch pounds = 10 foot pounds. That does not compute. Get out the service manual. YEP, that's what it says, and the metric equivalents agree, at least by eyeball. Amazin. It must have something to do with the V6 putting the cotter pin through that sheet metal hat while the V4 puts the cotter pin through a slot in the nut. Chuck
Peter	posted 07-28-2005 07:34 AM ET (US) I'm with Tom on this ... a torque wrench isn't necessary. In all the many, many years I've been boating with outboard motors, changing removing and reinstalling propellers on motors from 4 HP up to 225 HP of various brands, I've never used a torque wrench to tighten a prop nut and I haven't lost a prop yet.
jimh	posted 07-28-2005 09:07 AM ET (US) OK, make that 99-percent of the time people don't use a torque wrench. I bought the 1-1/16-inch socket because my floating plastic wrench was getting a little sloppy. The suggestion to re-check the tightness of the propeller nut after running the boat is a very good one.
bsmotril	posted 07-28-2005 10:11 AM ET (US) If the prop is snug on the shaft, this method will sometimes help break it loose as long as the corrosion is not very bad. 1) Put the flush muffs on the motor, hook up the hose, and make sure the hose is clear of the prop. Make sure the motor is vertical. 2) Put the prop nut and washers back on until they are finger tight snug to the prop, then back it off 1/2 turn. 3) Start the motor up and run it at idle speed in neutral. 4) Double checking the prop area is clear, and you have water flow out the aspirator first, shift the motor into forward, gear, then to neutral, pausing a few seconds, then into reverse. Repeat this a few times. 5) Shut the motor down, and check the prop. If it is not loose now, you'll have to resort to the other methods mentioned here. This works best on heavy stainless steel props where their mass and inertia helps to break loose the corrosion between the prop hub and prop shaft. BillS
Matthew	posted 07-28-2005 11:28 AM ET (US) Check to make sure that the thrust washer hasn't stuck to the engine side of the old propeller when removed. You will think that the new prop went on "just as the old one came off", but you will be missing an important component.
John W	posted 08-01-2005 11:06 PM ET (US) Thanks for all the replies & advice. I'll be changing the prop this weekend & will follow the tips here. Thanks again, John
kamie	posted 08-02-2005 02:46 PM ET (US) I suggest the metal prop wrench, the plastic ones strip if you change props a lot or your got a prop nut on really tight. The other handy thing is to take a length of 2X4 and drill 3/4 inch holes in each end. That way you can put a spare dock line through it and tie it off to the stern cleats. Very handy if you ever need to lean over and remove the prop from inside the boat. You can tilt up the engine, thread the board between the prop and the cavitation plate, tie it off and still have two hands, one to loosen the prop and one to hang on so you don't fall out. kamie.homeip.net/prwc/Evenstar/Misc_Evenstar/misc_evenstar_7.html As for torque wrenches, that is way over kill. I have yet to loose a prop because it slipped off. I have lost a metal prop wrench, so keep an eye on those.