Drilling out the boss on Left Cyl. Head

[rnd5553]

Does anyone know the drill and tap size to use when drill out the BOSS on the left side (drivers side) cylinder head on a 1966 110HP. This would be to be able to install a thermister and adapter that I have from Clarks.

I don't want to lose the use of the temp gauge idiot light, therefore, I need to retain the temp sending unit on the right side that's already there. This is to install the Corsa dash in a Monza. Thanks

Thanks

[64powerglide]

Here is a chart, you just need to know the thread size.

[Scott V]

Does anyone know the drill and tap size to use when drill out the BOSS on the left side (drivers side) cylinder head on a 1966 110HP.

3/8-16..............answered your question here: viewtopic.php?f=55&t=11870&p=80936#p80936

-Scott V.

[b74eqcm]

I don't get it. Didn't your question about mounting the thermister get answered in your other thread? If you have the adapter from Clarks and a thermister, you're set. No drilling required.

[cnicol]

[dixon5553]

no I did not, I need to run the thermistor and retain the temp switch too from what I understand. Thermister does not operate the CORSA dash's idiot light. Let me know if this is not the case.

[bbodie52]

The warning light switches are just that... on/off switches. Both the right head temperature switch AND the oil pressure switch are wired to the same bulb in the instrument panel. Power is applied to that bulb when the key is ON, but it needs a GROUND to complete the circuit and to turn the bulb on. By default the temperature switch is ALWAYS OFF as long as the head is not overheated, so it never provides a ground to illuminate the TEMP/PRES bulb. However, the oil pressure warning switch is ALWAYS ON (CLOSED) unless oil pressure is present (engine running). In this way the bulb is automatically grounded by the oil pressure switch as soon as the key is turned on but before the engine is started. This serves as a BULB TEST each time the key is turned ON. When the engine is started, oil pressure turns the TEMP/PRES bulb OFF.

The thermistor on the left head is completely independent and unconnected to the warning light system. Instead of functioning as an ON/OFF switch, it functions as a variable resistor that permits variable electrical current to flow from the cylinder head temperature gauge to electrical ground as the temperature of the cylinder head varies. This current change is registered as indicator needle movement on the cylinder head temperature gauge. It essentially functions in the same way that the gas gauge responds to the variable resistor in the gas tank sending unit (connected to a float).

Spyder Wiring Differences

Engine Compartment Warning Light Switch Wiring

This wiring diagram for the Corsa/Spyder warning light and gauge system is more complex than what you will be installing in your Corvair. It has an added warning buzzer that is triggered ONLY by the temperature switch in the right head. The silicone rectifier (diode) prevents the oil pressure warning switch from triggering the warning buzzer. I sometimes wonder if ANY Corsa (or Spyder) owner has EVER heard that buzzer go off! In any case, you don't need it. You just need a single wire from the Corsa cylinder head temperature gauge connected to the thermistor in the left head (along with the power wire to provide voltage to the gauge and on to the thermistor).

Corsa TEMP-PRES Schematic Details

[ac1948]

Both heads are already drilled!!!
Jerry