To be sure silver, the Rollfast is no longer jackshafted, I've removed the "shiftkit" & freewheeled crankset, making it a direct drive single speed... should I find a Maytag or Villiers engine to replace the engine it has now, I'll use the jackshaft design the taddy has instead.
As the taddy's jackshaft is just a bit of 5/8" keyed shaft, a coupla 499502HNR sealed bearings, sprockets & lock collars and a "BMX" style freewheel for the pedal chain, all mounted through a tube (an old bottom bracket in this case), there's no flex at all, no engine drive force on the freewheel...
...and the result has given me years & thousands of trouble free miles, I've not needed to fix or even maintain it, aside from chain lube ofc lol
All of the components are "off the shelf" hardware store items except the BMX freewheel but even should that freewheel fail, it's a very inexpensive & easy repair as it's not a "specialty" part (mine's a generic BMX, it was like $12 or somethin') & it's right there, don't even need a puller tool. Gearing changes are easy too, I did change the secondary engine cog a few teeth around midsummer or so jus' to see if I liked it better.
Here's a vid & a pic, bear in mind it looks more complicated then it is because of the "extra" derailleur I'm using for a pedal chain tensioner
https://youtu.be/U10xLqTekOw