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Rebuilding the Water Pump ( ST1100 ) *

Started by KoTAOW, June 27, 2018, 10:26:09 PM

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Submitted by Terry Smith, STOC #8901


Rebuilding the Water Pump ( ST1100 )

Complete water pumps are unavailable for the early ST’s new, but I was able to find a vendor on
eBay, who sells a rebuild kit for GBP68.99, shipped to anywhere. 

Ebay store is located here:

Web page here:

Some of the photos below are from the vendor’s website. The same kit can also be used on later model ST1100’s. The vendor (Alan) was helpful via text using the number on his website.


The water pump seal and/or the o-ring on the pump housing began leaking on my 28-year old bike
at around 125,000km.

The pulley and impellor get re-used, so need to be pressed out of the original housing.

The parts supplied consisted of a new shaft and bearings, ceramic seal, stationary seal and rubber
seal for the impellor.

To access the pump, you will need to remove the bodywork, drain and remove the radiator, then
remove the timing belt covers and the timing belt, plus the tensioner and idler pulleys. You will also
need to remove one of the cam pulleys and the cover that bolts to the cylinder head (I did the left
side), without that you have no way of getting the pump housing out of the bike; you will probably
need a new gasket for this one (14525-MY3-000). I also ordered a new pump o-ring (19226-MT3-
) and the idler pulley (14560-MT3-003) as that had a loose bearing.

Once the 7 bolts are removed the pump housing can be removed from the front of the engine, I
used a pry bar to get it moving. I disconnected the oil-cooler water hose at the cooler, plus the hose
guide that shares the case bolts, as it was impractical to get it off the water pump housing in place.

The instruction supplied by the vendor show the use of a hydraulic press to separate and reinstate
the parts, I don’t have access to a press so relied on using a large hammer.
Firstly, support the pump housing well, close to the pulley, with the impellor facing up, then drive
the shaft/bearings out by pressing on the end of the shaft visible through the hole in the impellor. I
used a 5mm allen key bit mounted on the end of a short extension bar of my ½” socket set. The
socket on the end of the extension bar took a bit of a beating but is still usable.

This required some big hits to shift, and the vendor recommends heating the housing by pouring
boiling water onto it which will make the alloy parts expand (you could also heat it in an oven,
apparently that will stink up your kitchen, you have been warned).

After the first bit of movement the impellor will make contact with the housing and then slide up off
the shaft, and can be removed. You can switch to an 8mm socket bit and continue to drive the
shaft/bearings fully out of the housing.

You now need to separate the pulley from the shaft; support the pulley well, then drive the shaft out
of the pulley fully using the 8mm diameter bit.

You can now drive the old seal out of the housing using a 16mm socket. I cleaned up the pulley
bearing housing with fine sandpaper to make reinstallation easier and added a little grease. I took
time to clean the pump housing fully as well. This includes the two weep holes at right angles to the
shaft axis.

I drove the new bearing and axle into the pump housing using a 22mm socket, until the surface of
bearing was flush with the edge of the housing. To make this easier I heated the pump housing with
a hot air gun, and chilled the bearing/shaft in my freezer first.

Flip the assembly over, and gently press the pump stationary seal into the housing using a 22mm

Now the pulley can be re-fitted, driven onto the shaft which I supported well from below so all the
load is transferred to the support, not through the bearings. The pulley should be driven until the
shaft projects by 1mm.


The impellor should be checked/trued for flatness in case the removal process bent it; mine was

The rubber seal is now fitted into the impellor hub with a small amount of silicon sealer, then the
ceramic seal is fitted. The seal has a glossy side, and a machined matte side; the matte side should
face the stationary seal in the pump housing. Don’t apply any lubricant other than coolant to this

The impellor is now placed on the shaft and driven home, again the shaft needs to be supported
from below so no force is imparted to the bearing. There was a final clearance of about 1mm
between the pump housing and the impellor.


And…you’re done.
You will find that the seal is a little stiff (it is lubricated by coolant) so the impellor won’t turn that
freely. Don’t panic.


Thank You again for your contribution Terry Smith, STOC #8901