You are reading a single comment by @Jung and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Jung
pdlouche
Went down a rabbit hole regarding piston slap.
The Rotax 237 inside the Scorpa Easy (project bike... btw I have a project bike) is rattly as hell. I expect it is piston slap, because it is top end and metallic.
Need to order fresh gaskets before I open the top and investigate, but I am expecting to see a big gap in the piston vs cylinder.
Reading online, back mid-20th century, there were two 'old school' methods to reduce piston slap before going down the bore/hone/piston route. One was to knurl the piston, and the other was to clamp the skirts in a vice to spread them slightly. Both achieved a greater circumference to reduce slap.
I am expecting the 'no no no no no no nope nope noooop don't do it' but I also wondered if anyone was old enough to come across a mechanic who had done it.
The Scorpa's Rotax engine is just short of obsolete anyway.
Edit: https://www.practicalmachinist.com/vb/general/knurling-pistons-384013/