Thinking back on the original question about low compression. What is "low compression"? The reason for the question is because most of the manufacturers have not established numerical criteria for compression values in their engines. They have compression, or they don't. They run, or they don't. Another issue that comes up with compression is how it is measured. Two people can have engines identical in every way, use the same compression gauge to determine peak values or leak downs, and have different results. The same compression gauge, set up and installed only slightly different, will provide different results. If you have a hose attached to the end of the gauge you will obtain a lower value than someone that has a straight plug adaptor on the end of the gauge.

How does one check compression by flipping a prop? Do you flip in the running direction or opposite the running direction? The answer here is to flip opposite to the running direction because that is the direction the ring was designed to provide the best seal. Note that rings are beveled on one side for that purpose. Never check compression with a dry engine, and never check by wetrting the inside with straight oil. Both methods provide incorrect values. Check compression using the same fuel mix you will run the engine with.