47 x 15 sprocket set up and chain

[eadmr04]

I’m currently running a standard Italian GP 200 gearbox but am changing to an SX200 gearbox and want to run a 47 rear sprocket and 15 front to get a ratio of something close to 4.9. I’d rather achieve this via this method rather than going down the route of GP box with 47 x 19 as I don’t want it quite as revvy. This is to try to help reduce wear and tare. I believe I need a “stretched” 80 link chain to get this to fit. I’ve checked some of the older chains I’ve got but they’re a bit too old and tired. Where can I get a new chain to fit or how can I get a new one to stretch so I can utilise it? Is there a method of stretching them?

[Storkfoot]

I strongly suspect you need an 81 link with a pull down tensioner. A stretched chain is basically just worn out.

I have built an engine recently with a 48/15 set up on the same gearbox to get a final drive ratio of 5.0. Sticky’s book said an 81 link should work. It didn’t. I had to use an 82 link with a pull down tensioner. It was a new IWIS chain.

I haven’t run this engine yet.

All that said, if I could get the same final drive with a GP200 gearbox and a bigger front sprocket, I’d personally go with that. A bigger front sprocket should make easier kick starting and should be easier on the clutch.