If you would like to make a Paypal donation to support this forum, click on this button

Main Menu

How to replace the Water Pump Bearing and Seal ( ST1100 ) *

Started by KoTAOW, June 28, 2018, 02:15:12 PM

Previous topic - Next topic


Submitted by Alan Wilson, STOC #XXXX
Location:8 Grahamsdyke Road, Bo’Ness. West Lothian. EH51 9EG
Contact email:

Original article is located here:


How to replace the Water Pump Bearing and Seal ( ST1100 )


Parts available on ebay at this link:

Price: GBP 49.99
Approximately US $66.15 (June 2018 )



You will need a small press for this, don’t try and use a vice or large mallet.

The hotter you get the pump casting the easier the bearing will press out. So remove the rubber band seal and idler bearing.

Decide now where and how you will support the casting in the press. It must be very close to the bearing.

Put the pump assembly into your kitchen oven and cook at 200 C for 10 mins, do that when the wife is out because it will smoke a bit.

Use gloves to remove.

Make sure the casting is well supported close to the bearing when you press, if you see the casting flex, stop because you haven’t got it supported well enough.

Read though these instructions a few times to make sure you understand the steps, they were written with mechanics in mind not for someone who thinks you press with an ironing board.

1. Press the bearing out using a 4 or 5 mm hex ½”  or 3/8”  socket drive.

Press though the hole in the fan end just as far as the length of the hex will allow you.

Any other attempt at removing the fan first will damage it

If you didn’t use the oven pouring some boiling water over the casting will loosen the bearing.

2. Once you have pressed the length of the hex key, raise the press and lift off the fan.

3. Finish off the pressing using a 1/4 "drive long 8mm socket, the bearing will fall out below.

4. Press or tap out the seal cup using a socket.

5. Press off the pulley from the bearing.

6. There are two bleed vent holes between the seal and the bearing, and the outside edge of the pump, make sure they are clear.

They tend to corrode closed due to the seal leaking and are a pain to clear but has to be done.

One is shown with a screwdriver, the other is show at about the 7 O’clock position

7. Reassemble, Press in the new bearing from the pulley side until the edge is flush with the casting. Use a 22mm socket.

8. Press in the new seal cup using a 27mm socket.

9. Press on the pulley wheel until the shaft protrudes by 1mm out of the pulley.

10. Put the fan onto a flat surface and check the blades are straight, they will probably be bent a very little so straighten them out.

11. Remove the old seal and clean out the hole. Fit the new rubber seal into the fan using a little silicon sealant, this maybe a tight fit, looser is best so don't force, rub the rubber seal around the edge with some sand paper to achieve a "fall in fit" if required.

Fit the white ceramic washer, the side with the black marking goes against the rubber, don’t mix it up or the seal may not be water tight.

12. Press the fan fully onto the shaft.

13. Check the fan clearance, it should be about 1mm, closer is fine but higher risks the fan hitting the engine block. Make sure it turns freely.

It is lubed by the coolant so it will be a little stiff, don’t get or put oil on the ceramic surface, it can be contaminated and not seal.


Thank You again for your contribution Alan Wilson, STOC #XXXX