Since I posted, I found that kwhat I was thinking about was a device named, a two piece shaft collar. These look like they would do the job!
Frank
Not to pile on, but - no. The guys who do this for RC car engines use clamps that are exactly the right diameter, so when they squeeze it, it remains (mostly) round. Even then, it's an absolute last resort. Most of the engines you have that I know about have easily available factory spares, that is probably the way to go.
Outside the wildest coincidence, your split collars will be the wrong diameter, and crush the cylinder to a football shape. By wrong diameter, the tolerance is probably on the order of ten thousandths of an inch. Or, for the iron liners, crack them.
In any case, it seems inconceivable that you have worn out any engines, short of running debris through them, in which case the problem is not wear, but scoring. Even pretty modest and semi-disposable engines like the McCoy $10 jobs will last many hundreds of flights, a really good one, thousands (I know, I have done it). If the cylinder is scored, or otherwise damaged, squeezing will not fix it.
Brett