These heads are for 40mm carburettors and 38mm diameter exhaust pipes, i.e. 100cc bikes from 09/1980 to 12/1984, and also the R100/7T, built from 09/1978 to 09/1980. This price includes supply and fitment of a new exhaust valve guide to minimise the risk of a dropped exhaust valve due to guide wear. We can offer our usual six month warranty if the guide is replaced. Part can be supplied without a new guide fitted for £20 less, but we do not cover damage caused by dropped valves under warranty if you choose this option.