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74.5 and 77.6 psi are good numbers. Sounds like your new rings have seated properly and you are good to go with a little tweaking.
Well, actually…..
I’m almost too embarrassed to admit, but I was in a hurry when testing compression the last time. So, I just used the first drill at hand to crank the motor. And obviously, the faster you crank it, the higher the numbers are 😳. Rookie mistake.
Even though I was surprised by the sudden increase in numbers I gave it no more thought. The motor runs very nice now at moderate and high speed, but still won’t idle. So, another compression test (proper this time) gave me the same numbers as before. So too low.
I’ve tore my seized donor motor apart and was able to get the pistons out. Nothing appears to be damaged, cylinders look in perfect shape, so I’m cleaning it and will put it back together for a compression test. If the numbers are good enough I’m considering restoring it and swapping the power heads to see if that improves thing. Worst case scenario is that I have 2 low compression but running power heads