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Valve Travel

Reference Materials

Adjusting the Valve Travel (or Gap)
of the Standard Secondary Valves

Hi Ross,

This is a complex question because there are so many variables. First, the secondary Standard valves use force-fit collars to hold the valve facings in place. So, usually a jig is made that is used to position all of the collars in exactly the same place. Minor adjustment to the position of the collars is almost never done once the valves are put together. Second, as for establishing the correct placement of the collars, exacting measurements should be taken before the valves are taken apart. That way the exact position of both facings is known in relation to the bottom of the valve stem. (The top of the stem is generally not used as a reference point because the threads are not always the same from stem to stem.) Third, since the thickness of the intake leather valve facing, and all other associated intake valve parts varies depending on which materials are used, the position of the first collar (the one closest to the valve stem threads) have to be determined before the position of the collar can be ascertained. Forth, then the degree (or amount) of compression has to be determined before the position of the second collar can be ascertained. Lastly, before the collar for the exhaust facing is positioned, the exact thickness of the exhaust valve facing and backing plate must be known, and the minimum distance between the intake and exhaust facings (outermost sides) must be determined.

Generally speaking, the depth of the valve holes and the thickness (or recess) of the valve plates is virtually identical from valve to valve. However, that's not always the case, and that's why the minimum face-to-face distance is important. The face-to-face distance cannot be decreased once the collars are in place (except without much difficulty). However, paper punchings can be added between the exhaust face collar and the fiber backing plate if the valve travel is too great (between 0.035" and 3/64" -depending on whom you believe- I use 0.040" for Standard secondary valves).

Now to your question. As for measuring the travel, I use a thin metal washer that is exactly 0.040" thick. I rest the completed valve in place, lay the washer on top of the intake facing and then lay the valve plate on top. If the plate does not sit firmly on the valve board. That's a major problem. It means that the exhaust facing collar is too close to the end of the stem, and it must be reset (pushed further up the stem). If the plate rests firmly, then I gently lift the stem while holding the plate in place with one hand. If there's free play, then I will add paper punchings, as explained earlier, until there is no free-play.

Hope this helps.


John A Tuttle

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