In our class, on an Evinrude 7.5 7520, some of the piston rings were damaged and I was able to find a replacement set off ebay. We cleaned out the grooves and put the new rings in. One piston has 1 new ring, the other piston has 2 new rings. Only one ring was actually broken when we opened up the motor, but we broke two more trying to free them since they were impacted into the grooves.
I did a light hone before re-assembling. When turning the crankshaft by hand there are no rough spots, and it feels smooth, however there is definitely more resistance than the other motors that are worn in. Both pistons feel the same, one does not have obviously more friction than another. I put a digital torque wrench adapter on a 3/4 socket and turned the crankshaft, takes about 20 inch-pounds to rotate it. For comparison, I tried to take a reading on another similar motor that is smooth-as-butter, but the torque wrench won’t read anything less than about 16 inch-pounds so I couldn’t get a comparison reading.
This is my first time putting new rings in. Is the extra resistance normal, and will it work itself out after a “break in” period? My gut tells me it will be ok, but if there is any advice please let me know, I’d hate to seal up the powerhead and have to take it apart again.
Thanks!
Well, I would not replace just one of the rings, either replace all of them, or none of them. But, on this engine that has low compression/RPM to begin with, I wouldn’t worry about it. The important thing is that it rotates smoothly/evenly through the entire 360 degrees of rotation, which you report that it does.
