no increases in cc or performance Tim, it is purely to allow for parts availability. later model (1987 onwards) crankcases have a 5mm higher cylinder base cast into the cases compare to 85/85 model. because of this the conrod kits are different. so you can use the spacer plate on 85/86 models and the rod kit from 87 onwards.
1985 was the High compression model and each year after that honda decompressed the CR500 slightly on every model until around 1988 to make them more rideable. That is why the sidecar boys only want 85/86 models for the lightweights back then tim as they had a few more horses and it would have been very noticeable on a sidecar with the extra weight. Bill Williams and Bruce Linsdall won the 1987 1000cc aussie title in Tassie at Bryant Park Smithton on a 86 CR500 EML.
top pic is 85/86 cases lower is 87 onwards.
