K water/oil pumps

All K bikes from the first K100 through the K1200LT have the same basic pump mounted on the front of the engine. There were some changes during the years but the pump itself is mostly interchangeable. It's a two-part pump; the front section is a centrifugal water pump and the rear section (flush with the engine block) is a gear-type oil pump. The engine drives the small oil pump gear, which meshes with the larger gear, which drives the impeller via a shaft connecting the two. The shaft runs through seals at the point where it leaves the oil pump and where it enters the water pump, so when either one leaks you get fluid in the space between them. This drips out through a hole at the front of the oil pan, letting you know that the pump needs attention.

Parts-wise, they are rebuildable for about 10~25% of what a new pump costs. A rebuild involves replacing the two seals for the main shaft, two O-rings, and sometimes the shaft itself due to corrosion. On pre-1990 pumps you will need to replace the impeller and buy the impeller spacer.

The motor in the F800GS and similar models also uses the same water pump seal.

Design History

Initially the tip of the shaft was externally threaded and the impeller was held on with a nut, but starting with the 1986 model year the shaft was internally threaded and a bolt was used. The old shaft is obsolete and replacement shafts require the bolt.

oil pump gears
The drive tang on the small oil pump gear drives the larger gear and therefore the water pump impeller on the other side. Also shown is the large 32t gear from a 1990~1997 pump.
Stamped impeller on the left, cast impeller on the right. The spacer is used with the stamped one to match the overall shape of the cast one, and was shortened when the water seal was updated.

In January of 1990 the pump was redesigned. The cast impeller was replaced with a stamped steel one and a spacer. The gears in the oil pump were changed, which had the effect of slowing the pump down. Note that if you need to replace the shaft, you have to buy the right one to match your pump. If your pre-1990 pump was replaced at some point, it may be the later version.

Just to make things interesting for us, BMW returned to the earlier gears and housing for the European police K1100LT and then all K1200 models, probably because the faster gearing increased the coolant flow.

coolant seal
New seal on the left. The top part grips the impeller shaft and the bottom part is pressed into the housing. The spring keeps the two carbon slip rings (just above the spring in this photo) pressed together.

The other significant change is the design of the coolant seal. This has always been a two-part seal (one part is sealed to the shaft and one part is pressed into the housing) with lips on each part held together by spring pressure. The current seal is either a KACO AXIA AAHU 12x30 or an equivalent SIMRAX. Either is taller than previous seals, requiring more room than the earlier impeller or bushing provide. The early impeller or bushing cover about 9mm of the shaft, while the new seal only leaves about 7mm exposed. Use of the older parts will push the inner part of the seal too far down the shaft, fully compressing the spring and crushing the seal. The new bushing is shorter, 9mm overall rather than 13mm, so it doesn't touch the seal. You can also shorten the existing bushing (using a lathe or a grinder) and accomplish the same thing. The length is not critical as long as it doesn't move the installed seal.

Parts required:

Rags and residue-free cleaner (like Brakleen)
Sealant (see sidebar)
11 41 1 460 328 Oil pump O-ring $2
11 11 1 460 392 Water pump O-ring 2
11 41 1 460 329 Oil pump seal 20
11 41 1 741 870 Water pump seal 32
11 51 1 464 902 Spacer bushing 11
11 41 1 461 173 Stamped impeller (needed for pre-1990 bikes) 21
Just for reference
11 51 7 676 371 Pump, 12/19t $907
11 51 1 464 900 Housing 12/19t 405
11 41 1 461 793 Impeller shaft, 19t 227
11 41 1 460 282 Drive gear 12t 209
11 41 7 676 366 Pump, 14/32t 907
11 41 1 461 178 Housing, 14/32t 363
11 41 1 461 183 Impeller shaft 32t 251
11 41 1 461 181 Drive gear 14t 221
12 31 1 460 853 Impeller bolt 40
83 30 0 401 624 BMW pump tool set 150

Repair procedure

Before you start, clean the area above and around the pump at your local car wash, using the soapy spray. Your job will be MUCH easier if the worst of the dirt and oil are removed before you start. Don't get too close, you just want to flush the area above the pump (between the pump cover and the timing chain cover) and get all of the oily road grit out of there.

Drain the coolant and the oil.

Since the oil has to come out, you might as well time the repair with an oil change, right?

1) Loosen the clamp and pull off the hose to the right of the pump, allowing coolant to drain into a bucket.

2) Drain oil, remove filter cover, remove filter.


With a 5mm allen, remove the 9 cover bolts. The cover should come off with nothing more than light prying at one corner. Some more coolant will come out.

Pull the sensor wire(s) off the sensors and out of the housing. Needlenosed pliers can help get the boot through the hole. Now that you have access, before proceeding any farther, clean the area above the pump. If you don't, you'll continually get dirt contamination into your work area. Doing this with the pump in place protects the oil system.

Remove the remaining bolts (two long ones in the pump, plus five around the edge) and pull the pump straight off the front of the engine.

With a 6mm allen wrench in the back side of the shaft and a 13mm wrench on the front, remove the bolt holding the impeller on.

Press the shaft out of the pump (the large oil pump gear is part of it). The cast impeller is a tight fit on the shaft, which makes the job a bit harder. An easy way is to thread a long M6 bolt into the end of the shaft and tap the whole thing out the back, out of the impeller and out of the seals.

Using a hooked tool, drive the water pump seal out of the housing. Make sure you don't scratch the aluminum! Then drive the oil seal out.

Clean everything. The gears, the bolts, the housing, the cover, and the face of the engine where the pump mounts. Use a scouring pad to clean the shaft where it passes through the seals. This is when you decide if the shaft is OK to re-use or not.


Installing the seals into the housing is the hardest part. If you do the job using the BMW tools or equivalent, both seals are installed with the shaft in the housing. Using alternate methods, both seals are installed first.

coolant seal tool
The BMW coolant seal installation mandrel.
Outer diameter 40mm
Step diameter 28mm
Inner diameter 12mm
Step depth 8mm

Install the oil seal, with the flat side out, until it bottoms out in the housing. The oil seal sits inside a lip; be careful you don't scrape the edge off the seal as it goes into place. The BMW installation tool provides a sleeve that keeps the seal centered in the bore as it's installed. With the BMW toolset, a protective nose is placed on the end of the installed shaft and the seal is pressed into place around the shaft.

Install the coolant seal (BMW method). With the shaft in place, press the seal down using a stepped mandrel (shown) which supports the inner seal 8mm back from the outer flange. This will result in about 7mm of exposed shaft.

Install the coolant seal (alternative method). With the shaft out of the housing, use a pipe (OD < 40mm, ID 28~31mm) to press the seal fully into place so that the metal flange is flush with the housing. Using a mandrel with a 12.5~16mm hole, press the end of the seal (with the housing) over the shaft until you have compressed the seal about 1.5mm. Roughly 7mm of shaft should be exposed at this point.

Install the bushing, impeller and bolt. Use a dab of blue Loctite on the bolt and tighten it to 33 Nm, holding the other end of the shaft with a 6mm allen as before.

Install the new O-ring onto the small gear and place it into the housing. Rotate the gears so that the drive tang on the small gear is at the same angle as the slot on the end of the balance shaft.

Re-clean the faces of the engine and the pump housing where they meet. These surface must be clean and dry! Make sure your cleaned bolts are ready, along with a 5mm allen and torque wrench.

Apply a thin film of sealant to the surface of the pump, place the red O-ring in place and push the pump onto the engine. You may need to turn the impeller back and forth slightly to make the gears line up. Install the two long bolts, snug them down, then install the five shorter bolts. Torque all to 9 Nm.

Thread the sensor wire(s) through the hole in the housing and plug them in.

Re-clean the faces of the pump and cover where they meet. Apply sealant, position the cover and install the bolts with one hand while holding the cover in place with the other. Snug them all first, then tighten all to 9 Nm.

The remaining three bolts (with washers) are for the oil filter cover, in case you forgot.

At this point you're done, and just need to finish the oil change, reconnect the lower coolant hose and refill the system with 40% blue BMW coolant (good for four years).

BMW tools for pump rebuild

seal knockout tool
Seal remover tool 11 6 721
Oil seal tools 11 6 723 with protective cap 11 6 722 installed in impeller shaft

The 83 30 0 401 624 tool set (was 90 88 6 11 720) for these pumps consists of: