Bodged a nice 48/38/28 chainset onto my Cannondale road bike to allow me to enjoy the steep local hills rather than half-killing myself using its original 53/39. (The bodging was having to make the double front mech work for the triple by filling a tab down, and I also had to add a shim under the 'b-screw' to get enough movement of the rear mech to stop a rumbling in the biggest 2 sprockets.)
I also wanted lower gears on my Cannondale CX bike so I replaced its 36 inner ring with a 34, and put a 12-36 (or was it 11-36?) cassette on to replace the original 12-30 (or was it 11-30?). I had to put a MTB rear mech on to cope with the big sprocket. The bodge was that a 9-speed MTB mech has a compatible pull-ratio for the bikes' 10-speed shifter!
A couple of singlespeed bodges ...
I took a couple of old cassettes to bits and used one of the sprockets at the back, plus a pile of spacers to hold it in place. By carefully selecting the number of spacers either side of the sprocket, I got a perfect chainline.
The chain tensioner shown (as supplied) pulls the chain down to tension it. It uses a spring to create the tension. I found that the tensioner arm bounced about on rough roads and I kept unshipping the chain. I bodged it by removing the spring so that I could use the tensioner to push the chain up instead. I added a thick washer on the mounting bolt which allowed me to adjust the tension manually and then tighten the tensioner in that position.
I had the same thought, but actually - the single sprocket came from a cassette, so it wasn't riveted to the others!
@colly had a single sprocket chew through his hub's splines on one forum ride. There was a comical moment when he was pedalling like mad to go up a hill but the chain wasn't driving the bike forwards. It might have been the freehub, only it wasn't - all the other gears worked fine!
Of course, normally you wouldn't be riding everywhere in just one gear, so any wear would be spread out over all parts of the cassette/hub splines!
I'm riding a new wheel now. The old one was used s/s for about 3 years and hadn't failed, but I couldn't get the lockring undone to service the freehub. I'll be happy enough if I can get 3 or 4 years use out of this wheel.
about 4" of wooden broom handle replacing the snapped plastic strut that held my mudguard on, blackened with marker so it didn't look quite so woody. The added benefit of this bodge was that I made the mudguard quick release so it was only on when needed... which it wasn't on that day.