13 Holes

[mulwyk]

I'm installing the boot cowl. Everything seems to line up ok, but all those holes in the firewall have me stumped.

I know the big hole in the middle of the firewall is for the fuel line, and the big hole just South of there is the cabin heater inlet, and then there's the 4 engine mount holes, and 4 more small holes that line up with the firewall support lugs. But after that there's still 13 more mystery holes through the firewall. What for?

I know one of the 13 holes is for the throttle cable...but which one? And another is for the carb heat probably but where's that go? And really, 13 holes?

I took a picture of the firewall and numbered all the mystery holes. Any ideas about what goes through which hole?

[Pearson]

Re: 13 Holes

Bob.

My airplane is about 30 minutes away, but I have pictures of when I was doing a top overhaul a few years back. I have attached the pictures for your viewing and I will warn you now, they are not very good quality. But from looking at these pictures, below is my best attempt at naming the mystery holes.

#1 Oil Press

#2 Not on mine

#3 Mine has it, but can't tell from picture what goes here

#4 Throttle

#5 Not on mine

#6 Oil Temp

#7 Tach Cable

#8 #9 #10 Not on mine, but I have seen voltage regulator & wires mounted here

#11 P Leads

#12 Not on mine

#13 Maybe Carb Heat

[Robert Lees]

Re: 13 Holes

I bet the compressions there are a bit down, Richard?

[Robert Lees]

Re: 13 Holes

Here's my firewall, looking aft (so I'm standing where the engine is):

[Hank Jarrett]

Re: 13 Holes

8, 9 and 10 were for a voltage regulator on mine too (as well as almost every plane I have seen with a wind generator). By the way, that is a lousy place for a voltage regulator! Batteries are VERY sensitive to temperature and voltage regulators are temperature compensated. If you put the voltage regulator on the hot side of the firewall it will charge the battery as if it is the temperature inside the cowl (that means HOT). Hot batteries are charged at higher voltages. If the battery is inside the cockpit, and the voltage regulator is on the firewall, you will overcharge the battery and boil it off. You will trash the battery about once a year.
If you want the battery to last, the best thing to do is put the voltage regulator right next to it (assuming the regulator is set right). That way the battery and regulator will always be the same temperature.
Get those regulators OFF the firewall and behind the seat with the battery, where they belong.
Hank