DaleH
FOUNDER of Classic Parker Forum
The pictures below should help you perform the waterpump impeller service on small OB motors to 25hp or so. Typically on motors this size the only replacement part is the impeller itself. All parts though should be checked for condition and these include all gaskets and O-Rings, the drivekey, waterpump housing, SS housing cup, and the SS wear plate, which is what the impeller spins against.
FYI - The same principles apply to the larger motors, but usually the OEM full waterpump service kit on bigger OBs also replace the wearplate, O-Rings, and other pieces, like the drivekey on some makes. Remember, the torque and duty cycle of a big V6 OB is tremendously harder on parts and part longevity than it is on a small horsepower OB. On small OBs, I'll do this every 5 years or so. This Nissan only took me 45-minutes start to finish, including getting all the gear ready and cleaning up afterwards.
Impeller Change – Tools Needed:Torque Wrench (preferred and if you know the OEM torque values), socket set & box wrenches (US or metric depending on brand of OB), screwdrivers, maybe a pin punch if you need to remove roll-pins, pliers, rags, disposable gloves, gasket sealing compound, and some waterproof synthetic grease, like Bombardier ‘Triple Guard’, which is the best and least expensive synthetic marine grease on the market bar none. Any Jap motor-branded marine grease is the SAME product, but usually had at twice the price! See Photo3.
1. Before you start, investigate your specific make and model on boating schematic websites such as http://www.boats.net/parts/search//parts.html . A review of the lower unit and cooling sections should tell you three things, (a) what parts you need to buy and (b) how many bolts secure the lower unit (LU) to the powerleg, and (c) how to get the lower unit fully apart, as the shift rod needs to be disconnected from the powerhead or powerleg to the lower unit.
Makes like Nissan have the rod join in front of the motor, accessible without removing anything, where the two rods are joined by a connection secured with a SS roll-pin thru each rod. Most older OMC models require one to put the OB into reverse, then drop the lower unit, and separate the 2 rods that are internal to the LU/powerleg. Merc, Sears, and Force come apart in a similar fashion, but every model or model year IS different! Again, review the schematics and if you fairly handy, you’ll figure it out.
2. Put OB straight up and down with room to remove the LU and put motor into neutral.
3. Remove bolts holding the LU in place.
4. Drop the LU, shifting it into reverse if the shift rod connection is internal to the LU and you can’t see it at first when the LU starts to drop. The LU should be free to drop now, where most drop free with just a little bit of force needed. But before you drop it free, make note of the watertube where the cooling water goes up from the pump to the powerhead. Look over this connection carefully and take pictures now if needed for proper reassembly.
5. Disconnect the shift rod and separate the LU from the powerleg. If needed, you may need to put the LU back up and secure it with one bolt and then tilt the motor somewhat or put it into shallow-water drive tilt position to give full clearance for the driveshaft to come all the way out of the powerleg. You can see from Photo1 just how long the driveshaft projects out of the LU on this 15hp Nissan motor.
6. Support the LU in something or prop it against something so you can work on it, a slatted patio table or vice works slick, if handy.
7. Looking down on top of the lower unit, see Photo2, you'll see the waterpump housing assembly held in with bolts, the driveshaft coming through the housing, and the watertube near it. Also check the watertube up inside the powerleg as the rubber seal should stay on the waterpump housing during removal. For proper re-assembly, make sure it is on the housing, cleaned and well greased.
8. Remove 1 housing bolt, see Photo4, and drop it back into the hole. How much it projects up is at least how much you need to clean, grease, and coat in gasket sealer to facilitate the next removal. Photo5 shows a bolt as removed, which was then cleaned, coated with waterproof grease, and then dipped in the gasket sealer. Doing such I have NEVER had a problem with a bolt removal in 40-something years. If you ever get a stuck or frozen bolt, you might need to break out a ‘heat hammer’ (torch) and may God be with you … as it can turn a simple 45-minute job into an expensive 8-hour job that might need a professional! For the record, on any OB I buy, new or used, I remove service bolts that I might need to remove later and treat them in this manner. An ounce of prevention saves a lot of hassle, time, and ca$h later …
9. Remove all bolts and lift off the plastic waterpump housing, ensuring the SS metal cup inside (if equipped) came off with it. Remove the old impeller. Check the drivekey, remove and clean it, then re-grease it well and re-install it. Check the housing and/or driveshaft for O-Rings, as most small OBs don’t use them, but if you had done your homework well you would have known before you started if you needed a new one. Most can be cleaned and re-used if treated gently and if in good condition, but note it for next time.
10. Clean and re-grease the entire length of the driveshaft before further assembly, but don’t grease the splines yet. Clean and re-grease the SS wearplate that the impeller sits on and spins against, then put the new impeller in place, ensuring that you have correctly engaged the slot in the impeller hub with the drivekey.
11. As a check BEFORE you do any re-assembly, you can shift the OB into forward, rotate the shaft clockwise, and ensure the prop spins in the manner to give forward motion. Most OB driveshafts are clockwise rotation, but who knows what odd-ball could be out there. Add a large dollop of grease into the waterpump housing cup where the impeller rotates, ensuring you greased all around the sides, as this aids assembly greatly. Then lower the housing into place, see Photo6, and BEFORE and WHILE you lower the housing onto the impeller, rotate the driveshaft clockwise (looking down on the assembly) to ensure that the impeller blades orient to the needed rotation.
12. Secure the waterpump housing with the bolts, torqueing them to spec, or using a box wrench, secure them all up equally snug. Don’t over-tighten them.
13. Grease the splines of the driveshaft where it enters the powerhead, but DO NOT add any grease to the very tip top or last 1/8” or so of the driveshaft. See Photo7. The mating hole in the powerhead is a blind hole and if you apply a lot of grease all over the splines & shaft including the very top, you can hydro-lock the two pieces together and never be able to separate them again, as you have created a vacuum in a blind hole. Future removal will be all but impossible!
14. Re-assemble the shift rod and LU to the powerleg, applying grease and gasket sealer to the LU bolts. Hopefully you took good notes or pictures so you know how it all goes back together. Uhhh, you remembered to clean the bolts first, right, before applying the grease & sealer?
15. Check gear shifting, put into forward, remove plug wire, pull through the motor or spin by hand, ensuring the prop turns for forward motion. Check reverse and check it goes back into neutral and that all is well.
16. Re-attach the plug wire and set her up on muffs or in a barrel and test the OB. For this I use and highly recommend a laser digital thermometer, monitoring the powerhead by the cylinder top(s) and the thermostat pocket. You shouldn't see any temp over 180 or so, but again, all models are different. But at least the $20 laser temp tool will alart you to a potential overheat condition BEFORE you destroy that motor. You’re done!
FYI, If the OB has a thermostat, this is the ideal time to replace that too. These are a simple replacement and all you need is a new one, a wrench, and some gasket sealer for the mating surface. I also treat these bolts as I do the waterpump assembly bolts.
FYI - The same principles apply to the larger motors, but usually the OEM full waterpump service kit on bigger OBs also replace the wearplate, O-Rings, and other pieces, like the drivekey on some makes. Remember, the torque and duty cycle of a big V6 OB is tremendously harder on parts and part longevity than it is on a small horsepower OB. On small OBs, I'll do this every 5 years or so. This Nissan only took me 45-minutes start to finish, including getting all the gear ready and cleaning up afterwards.
Impeller Change – Tools Needed:Torque Wrench (preferred and if you know the OEM torque values), socket set & box wrenches (US or metric depending on brand of OB), screwdrivers, maybe a pin punch if you need to remove roll-pins, pliers, rags, disposable gloves, gasket sealing compound, and some waterproof synthetic grease, like Bombardier ‘Triple Guard’, which is the best and least expensive synthetic marine grease on the market bar none. Any Jap motor-branded marine grease is the SAME product, but usually had at twice the price! See Photo3.
1. Before you start, investigate your specific make and model on boating schematic websites such as http://www.boats.net/parts/search//parts.html . A review of the lower unit and cooling sections should tell you three things, (a) what parts you need to buy and (b) how many bolts secure the lower unit (LU) to the powerleg, and (c) how to get the lower unit fully apart, as the shift rod needs to be disconnected from the powerhead or powerleg to the lower unit.
Makes like Nissan have the rod join in front of the motor, accessible without removing anything, where the two rods are joined by a connection secured with a SS roll-pin thru each rod. Most older OMC models require one to put the OB into reverse, then drop the lower unit, and separate the 2 rods that are internal to the LU/powerleg. Merc, Sears, and Force come apart in a similar fashion, but every model or model year IS different! Again, review the schematics and if you fairly handy, you’ll figure it out.
2. Put OB straight up and down with room to remove the LU and put motor into neutral.
3. Remove bolts holding the LU in place.
4. Drop the LU, shifting it into reverse if the shift rod connection is internal to the LU and you can’t see it at first when the LU starts to drop. The LU should be free to drop now, where most drop free with just a little bit of force needed. But before you drop it free, make note of the watertube where the cooling water goes up from the pump to the powerhead. Look over this connection carefully and take pictures now if needed for proper reassembly.
5. Disconnect the shift rod and separate the LU from the powerleg. If needed, you may need to put the LU back up and secure it with one bolt and then tilt the motor somewhat or put it into shallow-water drive tilt position to give full clearance for the driveshaft to come all the way out of the powerleg. You can see from Photo1 just how long the driveshaft projects out of the LU on this 15hp Nissan motor.
6. Support the LU in something or prop it against something so you can work on it, a slatted patio table or vice works slick, if handy.
7. Looking down on top of the lower unit, see Photo2, you'll see the waterpump housing assembly held in with bolts, the driveshaft coming through the housing, and the watertube near it. Also check the watertube up inside the powerleg as the rubber seal should stay on the waterpump housing during removal. For proper re-assembly, make sure it is on the housing, cleaned and well greased.
8. Remove 1 housing bolt, see Photo4, and drop it back into the hole. How much it projects up is at least how much you need to clean, grease, and coat in gasket sealer to facilitate the next removal. Photo5 shows a bolt as removed, which was then cleaned, coated with waterproof grease, and then dipped in the gasket sealer. Doing such I have NEVER had a problem with a bolt removal in 40-something years. If you ever get a stuck or frozen bolt, you might need to break out a ‘heat hammer’ (torch) and may God be with you … as it can turn a simple 45-minute job into an expensive 8-hour job that might need a professional! For the record, on any OB I buy, new or used, I remove service bolts that I might need to remove later and treat them in this manner. An ounce of prevention saves a lot of hassle, time, and ca$h later …
9. Remove all bolts and lift off the plastic waterpump housing, ensuring the SS metal cup inside (if equipped) came off with it. Remove the old impeller. Check the drivekey, remove and clean it, then re-grease it well and re-install it. Check the housing and/or driveshaft for O-Rings, as most small OBs don’t use them, but if you had done your homework well you would have known before you started if you needed a new one. Most can be cleaned and re-used if treated gently and if in good condition, but note it for next time.
10. Clean and re-grease the entire length of the driveshaft before further assembly, but don’t grease the splines yet. Clean and re-grease the SS wearplate that the impeller sits on and spins against, then put the new impeller in place, ensuring that you have correctly engaged the slot in the impeller hub with the drivekey.
11. As a check BEFORE you do any re-assembly, you can shift the OB into forward, rotate the shaft clockwise, and ensure the prop spins in the manner to give forward motion. Most OB driveshafts are clockwise rotation, but who knows what odd-ball could be out there. Add a large dollop of grease into the waterpump housing cup where the impeller rotates, ensuring you greased all around the sides, as this aids assembly greatly. Then lower the housing into place, see Photo6, and BEFORE and WHILE you lower the housing onto the impeller, rotate the driveshaft clockwise (looking down on the assembly) to ensure that the impeller blades orient to the needed rotation.
12. Secure the waterpump housing with the bolts, torqueing them to spec, or using a box wrench, secure them all up equally snug. Don’t over-tighten them.
13. Grease the splines of the driveshaft where it enters the powerhead, but DO NOT add any grease to the very tip top or last 1/8” or so of the driveshaft. See Photo7. The mating hole in the powerhead is a blind hole and if you apply a lot of grease all over the splines & shaft including the very top, you can hydro-lock the two pieces together and never be able to separate them again, as you have created a vacuum in a blind hole. Future removal will be all but impossible!
14. Re-assemble the shift rod and LU to the powerleg, applying grease and gasket sealer to the LU bolts. Hopefully you took good notes or pictures so you know how it all goes back together. Uhhh, you remembered to clean the bolts first, right, before applying the grease & sealer?
15. Check gear shifting, put into forward, remove plug wire, pull through the motor or spin by hand, ensuring the prop turns for forward motion. Check reverse and check it goes back into neutral and that all is well.
16. Re-attach the plug wire and set her up on muffs or in a barrel and test the OB. For this I use and highly recommend a laser digital thermometer, monitoring the powerhead by the cylinder top(s) and the thermostat pocket. You shouldn't see any temp over 180 or so, but again, all models are different. But at least the $20 laser temp tool will alart you to a potential overheat condition BEFORE you destroy that motor. You’re done!
FYI, If the OB has a thermostat, this is the ideal time to replace that too. These are a simple replacement and all you need is a new one, a wrench, and some gasket sealer for the mating surface. I also treat these bolts as I do the waterpump assembly bolts.