With a spare 3 HP Briggs & Stratton, we practiced the sleeving process at Central Roller. Using mild carbon steel tube stock that was readily available, I turned and polished the OD so it had .004" interference with the ID of the cylinder. I also beveled the bottom OD for ease of entry into the cylinder. For the actual sleeve, this process will be slightly different: the sleeve will be cast iron and the ID will be honed to ensure low surface friction between the sleeve wall and the piston rings. But, for practicing purpose, this was a useful experiment.
We heated the block in a 275 F oven for an hour, and allowed the turned sleeve to cool to room temperature. Jason and Mick were standing ready at a hydraulic hand press with the sleeve while I retrieved the block from the oven. Once I got to the press, Mick positioned the sleeve on the cylinder and Jason started pumping the hydraulic press arm. It slid in like a warm knife into soft butter. Well at first...
Halfway down the cylinder, the sleeve cooled and expanded to make the fit a lot tighter. I gave Jason a hand with the pump arm, and we were put to the test. When Mick gave the thumbs up to signal that we had reached the bottom, Jason and I were quite relieved. Bosley even smiled.

The block and sleeve on the hydraulic press

Top view of the sleeve in the cylinder

Bottom view of the sleeve in the cylinder

Piston Sizes: 148cc displacement B&S on the left, 49cc displacement Lifan (Honda-style) on the right

50cc Lifan engine

The trusty mascot Bosley, overseeing the day's activities

With emphasis on dropping weight, we were considering milling most of the Briggs block (cooling fins and valve assembly). This would make our block run hotter since we wouldn't be dissipating as much heat. Now how would that affect our engine performance? Let's think about this...
We know that the amount of air passing through the carburetor determines how much fuel will be drawn per engine cycle. Warmer air is less dense than colder air, so warm intake air should draw less fuel than cold intake air. If this is true, we would actually want warm air for sake of reducing fuel consumption rate. The trade off for consuming less fuel is the smaller power output (cold air will expand more than warm air).
This theory was the basis of this engine test. In the North Lab at OCAS, we used the Otto Cycle Lab test stand from Thermodynamics class (with Muthar's permission, of course!) to change the intake air temp and measure the time to consume a fixed amount of fuel. We found that it took 35 seconds longer to consume 25 mL of fuel when the intake air temp was 94 F vs 77 F. By removing the cooling fins we will drop some engine weight AND have a lower fuel consumption rate. Bye bye cooling fins!

Our Briggs setup on the test stand

Action shot
From left to right: Rusty, Dan, Dave, and Jason

Dynomite water brake

Mick's heating the intake air drum with a heat gun

Jason and Mick working hard

Engine Test