I have an old Tecumseh OHV155 engine on my riding mower and need do some work and need specs and torques for valve lash, head bolt torque, ring end gap, etc. I want to raplace the rings, lap or replace the valves and replace lower crankshaft seal and all the gaskets that I break loose. Is there a website with these part numbers and specs?

Hi,
Try the link below, scroll down midway and pick the 4 Cycle OHV Service Information to get the service manual.
Tecumseh Small Engine Specifications (http://www.smallenginesuppliers.com/html/engine-specs/tecumseh-engine-specs.html)
Peace,
Clarke