I just installed a rebuilt crank assembly (rebuild by Bill Bune) into the cases of a '69 AT1 I am restoring. I used a set of VINTCO crank bearings (I believe they have a good rep?), heating the cases and freezing the bearings so they dropped in, and then installing the crank using both heat and a puller by DEET (less traumatic for everything).
Since the VINTCO bearings came with both crank seals I thought I would go with them, but after I installed the left one I am reconsidering. 

The crank turned really easily on install. No binding at all. But installing the left seal puts a real drag on it ( ). The VINTCO seal is a true double lip/double spring seal. Meaning that I can see a retaining spring around both seal lips. The OEM Yamaha seal (I do have one) is not like this. OEM seal has a double lip, but if there is a spring I cannot see it.

The amount of drag the VINTCO seal puts on the crank is really surprising. The set indicates it fits multiple bikes, including real race bikes, so I'm wondering if the seal set would be more for one of them? I do have a new OEM seal I can install. It would be a shame to destroy the VINTCO one.

If anyone has used them before and have any feedback, I would appreciate it.

Cheers! 

I just checked them out online. $24.95 for both bearings and 2 seals. If it is the same size seal and was greased, I think it is worth a try. I know the stock seal gave me the same perception on my 74 125 I built recently, but worked out great.
Just a reminder to put that o-ring in on the crank right side.

seal sizes for x ref:
25x40x8
28x40x8

I highly recommend the double lip seals.  I have not tried the Vintco but I regularly use the Yamaha OEM (77-79 IT175) double lip seals.  

The AllsBalls crank kits with seals and bearings for the IT175 come with OEM seals, same brand as Yamaha.

Most seals have the size on them, make sure what Vintco sold you has the "25" size on it.  (I had an ebay seller send me a 24 x 40 x 8 once)

Appreciate the replys. I believe I have solved my issue (at least I hope so, time will tell...).

The seals were/are the correct size. I verified this beforehand by looking at the new and old seals and verifying the sizes are the same.

I did not think to put a little lubricant on the lips before installation ( ). So, note to self on that. But your thought was good. So I used the smallest eyeglass screwdriver blade I had and carefully slid it down between the crank and seal, being uber careful, and added a (very) few drops of Kroil (my favorite loose-juice), and then slowly moved the driver blade all around the crank end before pulling it out. After this the assembly moved as smoothly as I was expecting/hoping it would.

My thinking is that the first lip of the seal may have 'rolled' a bit, and that my actions with the small driver and lube helped that lip go into proper position.

Lesson learned for me was to add a bit of lubricant to the seal lip beforehand (I did when rebuilding the forks!!  ) as I used the crank install tools to push the seal in place. Using that tool I could not see the seal at all, so couldn't tell if things were going ok or not. A point to remember for the '70 AT1 build coming up.

Thanks gents!

When the cases are together & the right side crank nut tightened they generally need a 'love tap' on the mag side to release tension. It's all held over to the right side bearing but often the left side resists the final right side tightening. I guess it depends a little on how you go about assembling it all--bearings in case or bearings on shaft etc.