A TeeDee .051 cylinder that a .049/.051 throttle sleeve won`t fit

I bought ,on ebay, a used teedee .051, for intentions of flying & testing parts. I also bought another used teedee.049 for same purposes.
I began with the 049, retired the old #4 cylinder/piston set (in swap out for the bernies set I got) when I took it apart for my usual initial cleaning/inspection.
Yes, it certainly needed a bit of cleaning, the crank/case had some gum on it.

the 051 I intended to use with a throttle sleeve and allow the piston/cylinder set to finish off its lifetime before replacing, however I am going to use the teedee carb I bought from bernie instead of the ace ( cox049/051 as labeled)throttle sleeve, here is why......

The 051 cylinder looks the same as the 049`s on the exterior, however, the throttle sleeve will not slide up over the cylinder past the exhaust ports, the 051 cylinder is slightly tapered, but not to the naked eye.