Re: 1983 115hp evinrude knocking
Before you spend a lot of time diagnosing the problem, do a compression check. Your readings should be 120 lbs per cylinder. If you already have one cyl low on compression, it may be time for a teardown and overhaul. If the compression is solid, there are a couple of possibilities you can check for: 1. An engine can suffer from a lockup if the engine severely overheats. Once a piston heats up so much-it will lock up in the cyl til the engine cools down. You can check for overheats with a laser temp gun-measure the head surface temps. Normal is 145-155 degrees. 212 is overheating. 2. Also possible you have an issue in the lower unit. You need to run the engine without the lower attached to check for your noise. Once the lower unit is detached, put a garden hose end to the midsection water pipe and run the engine. If the noise is still there it is in the powerhead. At this point you will need to pull the heads for a visual inspection. 3. It is not unusual for these older engines (with high run hours) to have some amount of piston slap. While it may sound like a knock, it's normal and is not usually an indication of imminent failure. It may run that way for years. An overhaul with overbore and new pistons will resolve that problem.
