BioPatent Communications
Datsun 240Z Renewals
The Datsun 240Z sport cars below were junkers some years ago. These cars are
notorious for rust damage to the wheel wells and floor pans. I have purchased several
240Zs at a discount because they don't run. Later, I found they did not run because the
previous owner did not know how to adjust the double SU carburetion system.
This 1973 240Z is my comfortable
car. It has an automatic 3-speed transmission, air conditioning, 4 speaker stereo system
and a suspension with adjustable shocks. It was a junker that had to be towed home when I
bought it. Still, I paid a good price because the body was pretty straight and the
interior good. Hours after I got it home, I realized it wasn't running because the fuel
line was clogged with rust from the gas tank and the carburetors were way out of
adjustment.
In September of 2001, the head gasket blew releasing coolant water into cylinder
number 3. The one common problem with the near bullet proof L24 engine is cracking of the
aluminum head; generally from the thermal shock of water in an overheated engine. I
replaced the cracked head with a 1972 head from my green parts car. I didn't know it at
the time but the '72 head has a smaller combustion chamber and a higher compression ratio
than the original '73 head. In 1973, EPA regulations required reduced compression to
minimize nitrogen oxides that cause smog. This also decreased efficiency and power. With
the '72 E88 head this Z had to be run on premium gasoline to avoid knocking. While I had
the head off, I decided to replace the stock exhaust system with a header and 2 1/4 inch
diameter exhaust pipes. Proper fit of the new exhaust system took a lot of fine
adjustment. The Monza header required extensive grinding of the seal flange to clear the
thermostat housing and intake manifold plus grinding to match the ports. Building an
exhaust pipe that did not rattle on the floor pans or scrape on speed bumps meant cutting
and welding a dozen subtle curves to fit the contours of the underbody (next time I will
have a professional do it for about the same cost). This change made my "comfort
car" louder but it sounds good and has more high rev power. Ultimately, I
rebuilt this engine.
Installing
|Air-Conditioning| in this car was complicated. Air
conditioners work by pressurizing Freon gas to remove latent heat in a cooling heat
exchanger (condenser) as the gas turns into liquid. The liquid Freon is sent to the
interior of the car where it cools air as it takes on heat and evaporates in another heat
exchanger (the evaporator). I had an after market Borg-Warner AC system in my green wreck.
First, I had to remove the old Freon-12 without releasing it into the environment. A Freon
pump from an old refrigerator was used to pump the Freon from the AC system to an empty
propane bottle sitting in ice water. The evacuated AC system was disassembled into
components - pump, drier, evaporator, condenser. The evaporator housing was sealed with
foam and silicone caulking to the heater blower inside the car. Holes were cut in the fire
wall for Freon supply and return lines to and from the evaporator in the passenger
compartment. The condenser was installed in front of the radiator. The pump was mounted
with a bracket to the engine block for V-belt power from the crank shaft pulley. All the
Freon hoses were connected with double clamps. A new drier was installed in the high
pressure Freon line between the pump and evaporator. The system was evacuated with a
vacuum pump and closed up. The next day, the system vacuum reading was unchanged so I knew
the system had no leaks. With the engine at a high idle, I charged the system with fresh
Freon-12 through the low pressure side of the AC pump. Liquid Freon appeared in the drier
sight glass. Cool air began flowing from the passenger compartment air vents. Oooo, my
summer car.
This 1972 Datsun 240Z has been kept almost
completely stock. There was severe rust in front of the rear wheel wells, children had
played on the roof, the engine would hardly run and the left rear suspension control arm
was bent from some impact. The interior was in pretty good shape and, it turned out, the
engine was in good shape too.
The rust was cut out with an air chisel and grinder, then new sheet metal was MIG
welded into place. The body dents were mostly pounded out from behind. Doors were rehung
and locks rebuilt. I painted this car in my patio with stock color enamel plus clear coat.
The car was detailed with the best parts off my other cars. The rear suspension
control arm was replaced with one from my wrecked (not my fault) green '72 240Z. Some
parts, like door light switches and bumper rubber, were purchased from after market parts
suppliers.
The engine had consistent high compression across all 6 cylinders. I adjusted the
valves, set ignition timing and balanced the carburetors. Datsun 240Zs have two horizontal
flow SU constant velocity carburetors; front and back - 3 cylinders each carb. The
carburetors must be balanced for equal air flow to each bank of cylinders using an air
flow meter. I was happy when this $600 "junker" easily passed its last mandatory
smog inspection in December, 1998.
This red '72 240Z starts easy, has firm brakes and a light touch on the accelerator
pedal and steering wheel. It is a pleasure to drive even though the original push button
radio fades in and out a lot.
Below is my first Datsun 240Z before and after it was wrecked. It had a 5-speed from a
1978 280Z and I once had it to 128 mph in Montana at 5,000 feet altitude. Now, parts from
it enhance performance and decorate all my other Zs. RIP green Z!