Performing a compression test on the Yamaha 50HP outboard motor.

This video is a follow-up to the leak down test I performed on this same motor. I wasn't feeling very confident about the results I got from that test so went back to a good old compression test to see what results that gave me. This video shows how to perform a compression test on a Yamaha four stroke outboard. A compression test is an excellent way to assess the general health of a motor. If you don't have good compression (around 120 PSI), or the pressure in the cylinders varies widely then there isn't much point look at other problems until that is fixed. Low compression can be caused by worse piston rings, a blown head gasket or valves that aren't seating properly (in a four stroke). Here is a video on fixing the valves:    • How to clean and lap valves   Here is a video on replacing the head gasket:    • How to remove the cylinder head from a Yam...   Here is a video on replacing the rings:    • Changing the Piston Rings on a Yamaha 50HP...