Two thing break top rings. Insufficient end gap (.004" per inch of piston diameter required) or detonation. caused by too much timing or not good enough fuel. Top oil ring has nothing to do with using oil. It relates to compression pressure.
Nothing wrong with 40 wt oil. It is extra protection.
Lots of chrysler engines were used for wooden launches and are infact still running some without even an minor overhaul in 40 years. They are twin carb engines for the most part. They run usually at idle or wide open most of thier life. One hing that really is differnt is tey have huge oil sumps compard to a car engine and they run cooler of course with a constant supply of coolant. DId youb re te engine or just re ring it. D. Which rings did you use , wnat brand?
That is what I would wnat to know.Then we could go from there if you wish.
Re stroke length. Engine design principles generally be live that piston speed is the limiting factor. Under 3500 is good under 3000 is safe. That is not RPM it is feet per minute.
Take the rpm x the stroke in inches X 2 /12 = feet per minute.. I am sleepy so i will recheck this inthe morning to make sure i didnt error but as long as you are under this there is no reason to expct engine failure even at sustained running. given sufficient oil volume (oil being the bearings coolant ) and sufficcient cooling by the rad and water passages.
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