After reading all the responses to motor oil types/weights, my question is whats the reason for all the heavy weights? I will say I use to use the 20w-50 then heard and or read to go with like a 5w-30. So whats the best to use?

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A broken clock is right two times a day.

it's all has to do with where you set your clearence at my motor's turn a lot of rpm so the oil gets real thin when hot so i like 50 w oil whether it be kendell or valvalene around here kendell's hard to find

There are going to be varied opinions about this question. Like Rock Rock said, it has a little to do with how tight your clearances are when you build your engine. What the temperature range is when you run it and how hard you push it also need to be considered.
I personally never use a multi-viscosity in any air cooled engine. (including my lawn tractors) For general use you would want to use SAE 30. For 90+ degree days you might want to use SAE 40. I have built motors for guys set up loose, and they use SAE 50.
If you decide to use a multi-vis, I might suggest 10w30 or 10w40. Even 15w40 is good stuff. That's what I run in my big block Ford.
If you go with thick oil and the bearing clearance is not there, your motor will actually have premature wear in the bearings. When in doubt, use SAE30 and you will be fine.

Roy