Re: Johnson 150 fast strike compression
You maybe ok. Depends on the year. Early 60 degree V6 engines had even compression on all 6. Yours does not. A few years later, OMC made a change to the size of the head volumes for the two lower cyl. Not sure of the exact year, but somewhere around 1995 or 1996. As a durability enhancement-the factory enlarged the volumes of the two lower head chambers, effectively lowering the compression on cyls 5,6. If yours is around this timeframe, it's probably normal. On your engine, I'd expect factory numbers to be 126-128 on the top 4 and around 110 on the bottom two. You may want to run a can of Bombardier Engine Tuner through the engine-as your mechanic recommended. It may increase the compression slightly to bring them closer to "normal" compression ranges. Best to have them within 10% of factory spec.
