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The odd combined connecting rod/piston and getting the accurate internal securing ring mounts The three decimal places metric machining tolerances on some parts are a bit Jo
Did you get a full set of prints for this engine?
When I was working at my place of employment, I very often received from students or researchers, impressive CAD metric drawings toleranced to three or even four - sometimes more - places of decimals. Usually they were for making a wooden loudspeaker cabinet, or an angle iron bracket for hanging something from..... So, three places of metric decimals doesn't absolutely always mean what it says... ( I just made them to the nearest mm., and never heard a word of complaint...! ) But I don't at all believe that you couldn't make these engine bits, Jo.... Dave
maybe aim to build it to the specs given but if you missed them then the part could still be used rather than scrapped.
That's the difference between building for fun and production.