I am only running the Alt and the water pump/flex a lite pully and crank. All underdrive pullys. Is it ok to run the belt just around the alt and then the crank or will it spin the alt too fast or too slow?
Need a picture or diagram Jerry to understand what you're asking. You talk about a water pump, but then ask if you can route the belt around just the crank and the alternator. How's the water pump being driven? If it's a standard HO reverse rotation pump (like came with all the serpentine belt cars) then the grooved part of the belt needs to sit on the crank pulley and the BACK (flat part) of the belt needs to wrap around the water pump pulley. If you have it routed that way, have enough tension on the belt, and have enough contact area between the belt and the pulleys, it should work. But without a picture it's hard to provide any more guidance.
Jerry - you can't run it like you're showing unless you put a standard roation pump on it. If the water pump and the crank are turning the same way you need a standard rotation pump. If the water pump is turning opposite the crank you need a reverse rotation pump.
No - you can't run the water pump either way. The impeller is designed to move water properly spinning only in one direction.
The drawing shown is gonna be a challenge unless the tensioner is reveresed; it provides tension pushing DOWN on the belt, not up.