47 thou (1.2mm) thickness Stainless Steel Compression Plate. This really is a useful item andwill save you an awful lot of time with a fretsaw and file. Used to amend compression ratio, fitted to base of barrel.
It is not uncommon to have to make these up when fitting new pistons and trying to get the engine to a particular compression ratio. These plates are laser cut from stainless steel (they do not deform or damage as easily as aluminium) and are 1.2mm/0.047 thou), which for a STD bore 79mm barrel equates to an approximate reduction in compression ratio of 1.2:1 per compression ring fitted.
Should you require it, Some years ago I created a utility for my own use availabe from our RacingVincent website to work out compression ratios and spacers required. As always in the modern world - we take no responsibility for you using this, but if it helps, it can be found here: Compression Ratio Utility
Note: Do not forget that when fitting or removing compression plates, it is necessary to check the clearances on the vertical shaft assembly, and if necessary fit a different width top Oldham Coupling. Should you need to change couplings - we also sell these in different thicknesses - see our SOHC Vertical Coupling Section.
Final point - always check the oil holes on your barrel match up with holes on the compression plate - as there were some variations over the years. If so - just open holes up to match with a small file
These can also be used on the base of most OHV Norton Model 18 and ES2 Barrels, if wanting to change compression ratio - but again, check oil holes match up, as they can also be different