Do you have a pump that looks like this?

 We call it the Bow Tie Pump. This pump will mount to an engine that has a 7/8" round keyed shaft that is only 1-1/8" long. With this special shaft you only have 2 options for replacement pumps:

Comet VRX 2527 http://www.watercannon.com/p-3427-plumbed-comet-pump-vrx2527g7-25gpm-2700psi-3400rpm-78-hollow-shaft.aspx

Giant GXH2525A-069  http://www.watercannon.com/p-3369-plumbed-pump-78-gxh-25gpm-2700psi-3400-rpm-devilbiss-short-shaft.aspx