N.B. The first model year ST1100s’ water pump and crankcase breather system are unique/different than all other model years. The crankcase breather chamber is external (black box on the right side near the rider’s foot) while all other years’ is internal. And that water pump is for the ‘96-‘02 models without the oil cooler behind the oil filter. Using this water pump is possible with some modifications. If you can find the pump for the ‘92-‘95 model years it can be installed on a ‘91 without a problem.
Edit: I replaced the water pump on my ‘91 at 180K with a NOS and it looked like the replacement (regular coolant changes). The pump’s and the other two bearings ran smooth as the replacements, go figure. I may get the pump bearing R&R kit and have my original pump ready to install at 360K.
John
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