Do I need a new Brompton chainring (3/32 vs 1/8)?

the_hundredth_idiot

I'm replacing the chain and sprocket on my Brompton and I seem to be making a meal of what should be a simple task.

The Brompton is about 6 or 7 years old. It had a new chain and sprocket when I had it professionally serviced about 4 years ago, but hasn't been used much over the last couple of years.

I bought a new chain and sprocket. First problem was that the sprocket had 7 internal notches (Shimano fitting?) compared with the 3 internal notches of the old one (SA fitting?). But I returned that and bought a 3-spline sprocket which fits, albeit with a flange which the old one didn't have.

However, now the chain doesn't fit the chainring! The chain sits proud of the teeth of the chainring, which I'm assuming means the chainring is 1/8 and the chain is 3/32.

What's the easiest solution? Buy a new 3/32 chainring or buy a 1/8 chain? Would a 1/8 chain cause a problem with a 3/32 sprocket?

Thanks in advance

ugo.santalucia

chain is always cheaper than chainring. 1/8 chain should be OK with 3/32 sprocket... its the other way round that won't work (same problem as the chainring).
However, chain/sprocket compatibility can be black art... I had 3/32 chains that didn't work with 3/32 sprockets

the_hundredth_idiot

Yeah - I suspected that's the case - new chainring £25; new chain less than £10. And I don't think the chainring is worn enough to justify changing it.
Thanks