Question about rebuilding GT175 crossflow

[stratos285]

I'm rebuilding at 1990 Johnson GT175. Have installed the new pistons and attached the connecting rods to the crank but have not but the case together yet. When I turn the crankshaft, the pistons or connecting rods "pop" when they get to full stroke. Is this a problem or is this because I have not joined the case halves together and stabilized the crankshaft. I do have it bolted at both ends with the top and bottom seal plates. Don't want to proceed if this is a problem......

[boats.net]

The crankshaft not being secured can be your problem. I recommend bolting the two halfs together with out sealant/gasket, re-check for problem then move from there.