Longtail u-joints and sleeve bearings

I'm gathering parts for a longtail using a 6.5 Lifan motor. The weedeater conversion thread has been extremely helpful. I have check into every u-joint I have seen listed in this thread, the high torque needle bearing type from McMaster-Carr for example, and all the bronze/synthetic sleeves they offer. They ALL have a max RPM rating well below the rated RPM for a the Honda clone engines. The u-joint with the highest speed rating McMaster offers has a max rating of 2500 RPM. The bronzes sleeves even less. They carry a straight coupler rated for 6000 RPM but that still leaves the problem of supporting the shaft.
I guess my question is this, and I'm not trying to be smart here, have folks simply overlooked this or are they just crossing their fingers and hoping nothing bad happens. Or am I just too worried about it? (I don't think so.)
Anyone with firsthand experience with this type setup please chime in. Your input would be greatly appreciated.

 

Ran into the same issue myself not understanding the u joints. What you need to do is go to an auto parts store or tractor supply and find the yolk with your bore diameter to match the shafts and then get the correct universal joint. Then you will assemble it your self and you'll be in business.

 

Horsepower / versus time ??

That is your concern.

Do not worry about it. You will find out as you run the shafting. They get noiser as they wear out.

 

why support the shaft ..if you take a 10 ft length of 3/8 rod ..prop on one end and engine on the other and run it in water it will not fly about and hit you ..quite common on human powered craft ...just let it all hang out .....