K Bike Water/Oil Pump Rebuild

By Jon Diaz
Original Article Dec 1995
Updated May 2003

There is a small weep hole on the leading edge of the oil sump cover on all K bikes. This hole is a drain for the gap between the water and oil seals on a K bike water pump, and when one of the seals fails, its respective liquid will come out of the hole to warn you that total seal failure is imminent.

No big deal. Keep reading. :)

Order the following parts from your dealer: a seal ring for the water side, an oil seal for the oil pump side, a small o-ring for the oil pump gear, and a coolant o-ring for the engine block. Have these parts in hand before you start because dealers generally do not stock them! I would also get a new crush washer for the coolant drain plug.

Here's what these parts should look like:

old seal

Photo courtesy of Chuck DeSantis

However......

There has been a recent design change in these parts, and its possible that your dealer cannot get these for you.

Here's what the new parts look like. Notice that the water pump seal has a stamped metal body now, instead of a plastic cover.

new seal

Photo courtesy of Clif Lines

A slightly different work procedure is required to install these parts, which can be reviewed elsewhere on the K tech pages. Go here.

Anyway, these instructions assume that you were somehow able to obtain the old parts from Motobins UK or a similar source, and want to fix your old pump.

You must first drain the engine oil and coolant out of the motorcycle. Unplug the oil pressure sending unit and gently remove the protective rubber boot from the connector. If you have a coolant temperature sensor, remove the connector for that as well and remove its boot. Loosen the clamp for the coolant hose and detach the hose from the pump.

Once the coolant is drained, remove all screws holding the front pump cover. The cover is also held in place with silicone sealer, so you may have to pry it off. Be very careful when prying as this part is an aluminum casting and very brittle. Minor pressure should be required to get it off. Things will look a little ugly:

The Pump

Photo courtesy of the Brian Curry Archives

When the cover is off, you will be staring at the water pump impeller. At this point, loosen the bolt (or nut on earlier ones) holding the impeller and remove it. Don't remove the impeller yet, because it will likely be on very tight and it is easier to remove when the pump assembly is in your hands.

Now remove the screws holding the pump assembly to the engine block and put them aside. The pump may also need a little gentle prying as well, but you can use a little more force because it is a more robust casting. Remove the pump assembly, and pay attention to the oil pressure sending unit wire; specifically how it is routed thru the hole in the pump casting.

Here is what the pump looks like from the oil pump side:

Oily

Photo courtesy of the Brian Curry Archives

I would remove the small oil pump gear at this point, and then use an allen wrench in the large oil pump gear to turn the water pump impeller off. I gripped the impeller with a towel, and rotated the oil pump gear in a counterclockwise (loosening) direction until the impeller came off in my hand. Then remove the large oil pump gear on its shaft.

The two seals you are changing are accessible on the water pump side. Clymer says to tap these out from the opposite side with a screwdriver and mallet, and that is what I did. I would recommend that you do not get close to the pump casting at all with your tools though, as gouging the casting will mess up the mounting surface provided for your new seals. I pulled the old ones out with a combination of needle-nose pliers and tapping from the opposite side, which worked ok.

When the seals were out, I fully cleaned the pump housing with degreaser and a toothbrush. Get all the grease off the outside, all the leftover silicone on the sealing surfaces, and all the oil out of the oil pump side. After cleaning with this method, I then cleaned the internals with contact cleaner to ensure that all traces of grease and coolant were gone. I actually waited a few days to continue because I figured more oil would drip out....which it did.

Now install the new seals. Place the housing oil pump side down on a piece of wood because you will be tapping from the water pump side with both of these. The oil seal goes in first, and it should be installed so that the sealing lip points to the water pump side. In other words, the open part of the seal points down toward the oil pump gear. I used a 19 mm socket with extension and a mallet to tap the new seal in. Gently tap the new seal....it will go in without too much force, and make sure that it is seated all the way around. Cocking it slightly would be a bad thing.

Then it is time to install the water pump seal. This seal comes with a plastic cover over the works, and I used a 1 and 1/16" socket plus short extension to tap it in. The rubber side should point down. When the seal is fully seated, the clear plastic cover should break off. Sometimes the tabs attached to plastic cover will also break off during this tapping operation, so make sure you remove all the tabs that were attached to the plastic cover.....there should be eight of them. There will be a ring washer with internal rubber piece that you must keep track of, and make sure it goes on with the wide rubber lip toward the water side of the pump.

Here's what the water pump seal looks like after the plastic has been broken and splayed out, with the remaining solid part setting the depth:

Plastic Bits

Photo courtesy of the Brian Curry Archives

Before installing the oil pump gear, I would use emery cloth and clean up all the corrosion on the shaft. If the shaft is pitted heavily, it would be worth replacing (about $70 in 1995, now over $175!!!) since it won't seal adequately and you'll end up having to do all this again. My shaft wasn't terribly pitted and cleaned up nicely, so I reused it.

Here is an example of a shaft that was salvaged:

Pitted Shaft

Photo courtesy of Hank Barta

Here is another:

More shaft

Photo courtesy of the Brian Curry Archives

Gently push the oil pump gear shaft thru the seals, and pay attention to the ring washer on the water seal. It has a very tight fit and the rubber insert will try to knuckle under as you press it on, so pay close attention to that. When the shaft is thru all the seals, push it all the way on so it is fully seated on the oil pump side.

At this point you can install the water pump impeller. I pressed it on by hand, and it was difficult. Resist all temptation to hit this impeller with a hammer to get it installed.....just work it slowly with the heel of your hand and it will slide on.

Once the impeller is seated, clean up the bolt or nut, and after applying threadlocker, torque to the appropriate value. The bolt should be 21-27 ft lbs., but the nut is less and these values are called out in Clymer or Haynes. I torqued this impeller off the bike using an allen wrench in the oil pump gear and a torque wrench on the impeller. Its kind of a three-handed job, but get a helper to hold the assembly and it goes ok.

Install a new o-ring on the little oil pump gear, and you are almost there. Clean all mating surfaces with contact cleaner, apply a film of your favorite silicone sealer to the oil pump surface per the diagrams in Clymer or Haynes, install a new coolant o-ring in the engine block, and slide the pump on. Install all bolts finger tight, and then tighten in a cross pattern to 5-6 ft lbs.

Reinstall the coolant hose, oil pressure sending unit wire, and water temperature wire if you have that, and make sure the coolant drain plug has been reinstalled and torqued with a new washer.

Clean and prep the water pump impeller cover and pump housing, and apply sealant to the cover per the directions in Clymer or Haynes. Carefully install the cover, and install all the screws finger tight. These screws should also be torqued to 5-6 ft.lbs.

I let the bike sit overnight for the silicone sealer to cure, and refilled the oil and coolant the next day. Ride the bike, and probe the little weep hole with a q-tip to be sure that the leak is fixed, and you have performed your first water pump rebuild. :)

 

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