CLEANING UP WOOD HEAT FOR 1982-83

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Remember also that the location of the sensor will directly affect the temperatures that it will "see" at different burn rates. The midpoint of our sensor is 36 inches above the top of the stove . . . but bear in mind that different heater designs can change the relationship of stack temperature to distance up the flue. It's quite possible to position the sensor and operate the system totally by "feel", but we've found it much easier to have a thermometer to guide us.

While much of our testing was monitored by thermocouples and an electronic thermometer, we've used two other sorts of stack temperature gauges as well: Taylor Instruments' probe-type thermometers (retail: $25), and surface temperature thermometers (from either Taylor Instruments or Condar Co. for $11.95). We should mention, though, that the internal probe thermometer reacts much more quickly than the surface-reading units, and it's necessary to wait several minutes after a temperature change occurs in the firebox before expecting that difference to be indicated by a surface thermometer.

HOW TO BUILD IT

With the foregoing guidelines in mind, you can follow the assembly sequence for the components.

[1] Remove — using a hacksaw — the vacuum chambers from two Standard Plus VC-24A (retail: $5.60) distributor advance diaphragms (common to most 60's GM V-8 engines), and take out the springs. Then file the cut surfaces flat and deburr the edges so that they won't harm the diaphragms. Go on to hacksaw through each diaphragm's shaft at a point next to the 90° bend in the end, and file the cuts smooth.

[2] Take one diaphragm and saw of the bracket just ahead of the spot-welded tabs that mount it to the diaphragm body. (Be careful not to damage the shaft.) Set the bracket aside for later use, and file the tabs on the housing smooth.

[3] Grasp the shaft of the same diaphragm in smooth-jawed locking pliers (or an equivalent tool) and thread the shaft, with an 8-32 die, to a point 7/8 inch from the diaphragm. Then cut the shaft to a length of 1-1/4" (leaving 3/8" of thread).

[4] Take the second diaphragm and cut off the bracket at the point where it narrows — just beyond the bolt holes — then file the remaining part smooth, thread its shaft with the 8-32 die for 1-1/8", and discard the leftovers.

[5] Locate the piece of bracket that you cut from the first diaphragm, and saw it off at the index dimples in the broad section and, again, at a point 1/2 inch up the narrower portion. Then bend the piece 90° at the narrowing point, and drill a 5/32" hole in the center of the tab. This component will be attached to the outside of the remaining piece of bracket on the second diaphragm (using two 10-32 X 3/8" screws and nuts), so the 5/32" hole must align the shaft. Slip a 7/32"-O.D. X 2" spring (Balkamp No. 770-2123, available at NAPA stores for 50¢), cut to length, over the shaft on the second diaphragm and attach the 90° bend bracket.

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