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Member postings for Richard Kellaway

Here is a list of all the postings Richard Kellaway has made in our forums. Click on a thread name to jump to the thread.

Thread: Valve timing a 5" Tich
15/11/2020 22:30:49

I would recommend looking at EIM April 1982 where Jim Ewins describes Walschaerts valve gear in detail and how to set it. I redesigned the valve gear on my 'Mountaineer' in line with the article and the results were perfect.

Be careful as some of these videos can be misleading. For example in the video above:-

The method of setting the front and back dead centres using a felt tip pin is not accurate. You need to be more precise as a small rotation in the crank will cause the expansion link to move out of position, which he even points out in the video. You need to use scribed marks on the wheel and use a pair of dividers to find the mid point between the two marks.

Don't pay too much attention to the return crank setting being at 90 degrees. This is only applies if the expansion link tail pin is at the same height as the centre line of the coupled wheels. This is often not the case.

He is correct in saying that at both front and back dead centres there should be no movement of the valve when lowering and raising the die block. If this cannot be achieved it is likely to be caused by one or more of the following:-

  • Return crank position set incorrectly
  • Return crank length incorrect
  • Eccentric rod length incorrect
  • Incorrect position of expansion link tail pin hole (sometimes referred to as 'Backset' )

He refers to the use of a dummy/adjustable eccentric rod to try eliminate any errors. This should be treated with caution as changing the length of the rod is likely to require repositioning of the expansion link tail pin hole!

He is correct in saying the valve should be set so the amount of Lead is equal at both ends. In fact this is really the only adjustment you have available on this valve gear and no adjustments here will be able to compensate for geometric errors elsewhere.

He talks at the end about cut-off but does not explain this is determined by the length of the valve and reducing the length of the valve (same amount from both ends) will result in an increased cut-off.

I hope this will be of some use

 

Edited By JasonB on 16/11/2020 06:51:43

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