Comparing old and new valve timing

As a last post on the subject of correcting the valve timing on the Leak  Compound in Befur (prior to “sea trials” later in the year), here we will look at the results from the static (blowing) valve timing tests, and compare to the results prior to rebuild. But first a video of it running on air with the new timing…

I just updated this post to improve the pictures and ordering to allow simpler comparisons between old and new timing data.

For comparison you can see how it ran before here in this post from May 2016

Before and After Comparisons

As you may recall we have developed a process of measuring the “static” valve timing by blowing low pressure air through the engine and listening for the ports opening and closing as the engine is barred over.

We did this before the rebuild and now after the rebuild. The following spreadsheet shows the data we gathered and the pictures provide “before and after” timing diagrams using this data and the Visual Basic program we wrote to analyse the spreadsheet data.

Measured Data

Data from static timing measurment of rebuilt gear (click for large version)

Before and After Pictures

The “before” pictures are in the right column and the “after” pictures are on the left. Note the following:

  • General reduction in Admission times (red)
  • Much more regular Exhaust timing (~180-deg)
  • No more “overlapping events”, all good in a racing Norton, less so in a steam launch!
  • The vast improvement in the HP results (no more overlapping events!)
  • The (correct) reduction in admission periods (cut-off) as we notch up (although some delay in lead as a result of the crossed rods configuration)..
  • Much improved symmetry between top and bottom timing on LP & HP cylinders
  • Astern HP lead is still negative, slightly more adjustment needed on that eccentric..
  • Compare the first two pictures to see this all demonstrated on the HP topend running ahead in full gear.

(remember you can click for bigger pictures)

So, I think we can all this progress and argue that the revised valve sizing and timing are a good modification to the standard Leak design. (see last post for updated drawings).

Let’s hope Mr Maltby’s tongue-in-cheek comment “Well it should use a lot less steam Malcolm, let’s hope we haven’t lost too much power!”

1 thought on “Comparing old and new valve timing

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