Engine Blueprinting

‘Blueprinting’ is without question the most used and abused term in engine building. In a very strict sense, every engine is blueprinted. By what we simply mean that before an automaker introduces a new powerplant, the design engineers must transfer their ideas into drawings that will guide the pattern makers and tooling specialists. But this is an imperfect world, and not every component that falls off the end of the assembly line meets the engineer’s exact specifications. Drill bits and machine tools become dull. Grinding stones wear out. Gauges don’t always read properly. Lathes run untrue, and mills flex.

In any piece of machinery as complex and complicated as the internal combustion engine, all these inaccuracies add up. Sometimes the mistakes cancel each other out, and the finished part is just what the original blueprints called for. More often, they combine to produce a component that is often somewhat less ideal.

An assembly line is no place for a perfectionist. The vehicle manufacturers are willing to accept parts that are ‘almost right’ or ‘pretty close’. There has to be a reliable means of determining whether the part is ‘close enough’, and that’s what a tolerance figure does.

Which brings us back to the blueprints. All the critical dimensions are assigned to tolerance. Some tolerances are more critical than others. Machine tools and their operators occasionally have bad days. When this happens the problem of tolerance stack-up against the process. It’s possible for the individual machine operations to be within tolerance, yet the final part may be far out of spec. In many instances the acceptable tolerances cover such a wide range, it’s a wonder that any production engine is able to live a long and a productive life and yet millions do. Engines have an amazing tolerance for abuse.

The most basic form of blueprinting, then, is simply making sure that all of the factory tolerances fall within factory specifications. In the eyes of most knowledgeable enthusiasts, blueprinting an engine means not only checking clearances but correcting them as well. Careful blueprinting demands that the engine builder pay attention to how the hundreds of parts in an engine all work together. The engine builder must then recognize that changing one component has an effect on many other pieces. The term ‘blueprinting’ embraces a tremendous range of engine building skills. Even the most competent and professional engine builder continually discovers new tricks and techniques that will make his motors more powerful and more reliable.

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