vccomm, I see Kempe is in Adelaide somewhere, so he may be within striking distance of you, 50 km or so.
Kempe, if you post the details of your Model, Type and Code, plus a picture or two of your mower, it will be easier to talk about your options. I agree that repowering with a premium engine, such as an OHV Honda, will make your mower sweeter to use, but it will no longer be original. Repowering with a piece of excrement, such as several engines I can think of, may make it less convenient to use than it is now, as well as losing its collector value. Other engines range between these extremes.
I have some difficulty in believing that anyone would wear out a Briggs engine by using it on a light duty cylinder mower such as an SB45: it takes several hundred hours of use, unless it is run for a long time in a neglected state. More likely your engine needs a tune-up.
