Triumph 5 speed gearbox retrofitted to early unit or pre-unit cases 

I have tried to give some ideas on how to retrofit a 5 speed cluster into earlier 4 speed cases of the Triumph 650 unit. This works for both pre-unit 500 and 650 as well. A pre-unit 500 with a 5 speed is a great conversion. Not suitable for the 350-500 unit models. Hope this helps. I have it in written form on my site, www.bmcmotorcycles.com