I have a Ferret Mk2/3 that I bought last April with some known issues. After spending 6 months replacing all the tracta joint seals, rebuilding the brakes, and doing a plethora of maintenance that had been ignored for decades I finally had it up and running. After about a half hour of zooming around my neighborhood, just as I was in my driveway I heard an occasional banging noise with random repetition. Long story short, it looks like the #6 piston ingested some sort of chain link? I do not think this was due to my negligence, as to me it looks like whatever this part is, was imbedded into the piston for a while, and only after getting the ferret running and up to temp and under load did it work itself free and finish off the piston. I say this because you can see that the cracked edges are carbon fowled, and where it was imbedded is new and shiny. The old B60 was probably running with this busted piston for a while.Now the previous owner bought this Ferret and it sat for about 15 years. I never found the part as I was thinking it was oil starvation at first when stripping the block, so it may have hit the floor and became lost forever. Anyway I'm glad to report that after many months I have rebuilt the B60, and it fired up with no issues.