Adjustable Pushrod for Measuring Valve Geometry

With my engine tin ready to go and with one side of the engine mocked up, it's time to start focusing on the valve geometry. Jake Raby has an excellent article describing the process and the reasons for doing it on his website. The short version: there are a lot of variables that dictate the pushrod length (like cam base circle, cylinder shims, valve seat location, valve stem length, rocker post height, etc) - so the best solution is to accurately measure what the pushrod length should be - then make custom pushrods. To figure out what the length of the pushrod should be, I'm going to use an adjustable pushrod - this way I can change its length and measure what the valve does with a dial indicator. Here's my adjustable pushrod:

Adjustable pushrod that will be used for building a Porsche 914 engine

 

Now, this goes in our engine mockup:

Adjustable pushrod in Porsche 914 engine

 

And the dial indicator is set up to measure exactly how far the valve moves as the crankshaft (and camshaft) rotate:

Dial indicator setup to show valve lift on a Porsche 914 engine

 

Now, I'm already to measure, measure and measure some more. Jake recommends that this be done in a continuous 8 hour session with no interruptions... Maybe I'll get it done by the time my toddler goes to college.

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All pictures and text copyright 2008