Re: Evinrude 7.5 HP 1956-1958
Are your replacement pistons standard or oversize? If oversize, the world is your oyster. If standard, you need to find a virginal block. Another thing to watch for is main bearing to crank journal clearance. The factory built these bronze bushed motors with very tight tolerances, often .001 - .002". A serviceable block should have no more than .005" clearance. Since these motors do not have replaceable bearing inserts, you need to pay attention to these tolerances. An option, though not economically feasible, is to have the crank journals hard chromed in order to build the journals up. I can't think of any outboard that is worth the expense, but if your heart is set on it, that is an option. Here are some links to that sort of specialized service:
http://www.marinecrankshaftinc.com/ Another link:
http://milehighcranks.com/
After all is said & done, you still need to be aware of the time bomb in the drive shaft shock absorber. With the tension on the spring for more than 50 years, be prepared for sudden failure of the spring.
I am not trying to discourage you, I am merely trying to give you a heads up. I for one would love to see your motor completely restored & functional. I love these old motors. Best of luck with your project!
