4. Measuring Shims.
1. With the shims and collets removed from a valve you should ideally also have the measuring tools to accurately check which size shims you have (Picture below, left to right: opener shim, opener shim measuring tool, closer shim measuring tool, closer shim and bottom centre are the collets). The measuring tools are simply two adapters that slot into the shims. You simply:
a. Measure the tools and note the size. Each tool needs to be measured across specific points, which will be covered later, and not always the very top to the bottom.
b. Slot them into the relevant shim, measure both together and note the size.
c. The tools fit in and touch the point where the valve would make contact. Subtract the size of the tool from the total of both and what you have left is the size of the shim from the face to where it touches the valve.
2. Opener shim: The tool for the opener is simply measured from top to bottom as shown below. This measurement is then subtracted from the measurement of both the tool and the shim slotted together, also below. The result is the thickness or size of the shim.
3. Closer shim: The tool for the opener is not measured from top to bottom but from the shoulder to the bottom as shown below. The top of the tool sits in the hole the valve would go through and touches nothing but the shoulder sits where the collets make contact. This measurement is then subtracted from the measurement of both the tool and the shim slotted together, also below. The result is the thickness or size of the shim.
4. Move through all of your shims that required adjustment after measuring your clearances. To work out your new shim sizes, take the amount the clearances were out of spec’ by and if the gap was too big then add it to the shim size to reduce the gap. If the gap was too small then subtract it from the shim size to make the gap bigger.