1.
Go to Dissasembly
After about 200,000 miles, a 240Z usually requires an engine
rebuild. Actually, most of the major components such as the
cylinder walls and main bearings will hardly be worn and probably
meet specifications. However, compression readings for cylinders
may become uneven and oil consumption past valve stem seals often
begins. There may be some embarrassing blue smoke off the line.
Oil pressure may be almost nonexistent idling on a hot day.
Several times I have also experienced white (coolant) smoke from
a head crack or bad head gasket. The good news is these engines
are surprisingly easy and inexpensive to make young again.
This description of rebuilding a Datsun 240Z L24 engine focuses
on the simple tasks of replacing rings, seals and bearings in the
block. While you are rebuilding the block, the cylinder head
should be taken to a machine shop for a professional rebuild or
at least replacement of the rubber valve stem seals.
The Datsun 240Z L24 engine is a relatively easy to pull,
disassemble, inspect, repair and install. A complete basic metric
tool set plus a few specialty tools will allow you to do most of
the job yourself. An original Datsun shop manual (out of print)
or a good aftermarket manual such as a Haynes manual is critical
to successfully rebuilding the L24.
Dissasembly.
Run diagnostic tests such as
compression tests, coolant leak tests and combustion chamber leak
down tests before you destroy the evidence by tearing down the
engine. Clean the dirty grease off the outside of the engine
before you start. This will help keep disassembled parts clean
and allow you to spray paint the block while it is out of the
engine compartment.
An engine rebuild is easy to start. Unhook all the hoses,
linkages and wires between the engine and car body. But wait!
Have you ever seen a "basket case" engine or motorcycle
torn apart by some clod who forgot how to put it back together?
Use the shop manual. Place the screws, nuts and other parts into
labeled plastic sandwich bags as you go.
Make room in the engine compartment by removing the radiator, air
filter housing and exhaust pipe. Remove the alternator and
starter motor. Support the transmission on wood blocks, a dolly
or transmission jack (things will go easier if your transmission
support has wheels). Remove the 4 bolts that hold the engine
block and transmission together. (Later, you can view the clutch
components and consider replacement of the clutch disk, throwout
bearing and pressure plate.)
Pulling the Engine. If you don't have a wheeled "cherry picker"
to pull the engine, attach a 2 ton "come along" (tool 1
below) hand wench to your garage rafters to lift the engine. You
should run an extra 4x4 along side one of the rafter beams for a
strong lift point. In 2-car garages, the span is greater so a
strong 2x12 beam should be mounted on end across the rafter
beams. Extra metal braces should be added to strengthen corners
and joints. You don't want the triumphant moment of pulling the
engine spoiled as your ceiling falls in and the engine crashes
back into your beautiful Z.
Remove the clutch pressure plate and fly wheel. With the engine
suspended from the rafters, it can easily be mounted to a movable
engine stand ($50 and up). An engine stand allows you move and
pivot the engine around as you rebuild the block. Remove the
crank shaft pulley (a wheel puller is required), front case, cam
gear and cam chain. Mark the orientation of the gears and chain
to simplify reassembly. Remove the head bolts (10 mm allen
socket) and pull off the head.
Inspection.
A quick visual inspection of the
combustion chamber will tell you a lot about the condition of the
engine. Oil in a cylinder, from worn valve guides or piston
rings, will leave an oily black crust. Coolant entering a
combustion chamber through a blown head gasket or cracked head
will leave it cleaned of the crusty deposits found in the other
combustion chambers. Burned valves, burnt pistons and thrown rods
leave deep scratches, obvious cracks and molten metal.
Inspection for normal wear requires a set of
several specialized measuring devices. Check the block and head
surfaces for flatness using a good straight edge. A 1-inch
micrometer is useful to check diameter, taper and roundness of
valve stems. A 2-inch micrometer is needed to measure crank
journals (shaft bearing surface) diameter. A 4-inch micrometer
(tool 2 right) is used to measure piston dimensions. A cylinder
micrometer (tool 2 up) is slid into the cylinders to check
diameter, taper and roundness. With piston rings placed squarely
in the cylinders, piston ring gaps are checked with standard
feeler gages. Rod bearing and main bearing clearances can be
checked with "Plastigages". Plastigages are wax wires
to place on a bearing surface before torquing the bearing cap in
place. When the bearing cap is removed, the Plastigage wax wires
have been squished - tight bearings squish them flat and wide,
worn bearings barely flatten the plastigage. The bearing
clearance is read by comparing the squished Plastigage width to a
supplied chart.
Check your shop manual for specifications of acceptable
dimensions and clearances. If the head is flat and valves not
worn, it may not need machining by a professional shop but the
rubber valve stem seals should be replaced (see valve removal
illustration below). Piston rings and crankshaft bearings should
be replaced since they are very cheap and easy to install. If the
engine "blew up" or is excessively worn, the block
should be brought to a machine shop for necessary repairs such as
boring the cylinders or turning the crank shaft on a lathe.
Replacing Engine
Components. Rod bearings, main
bearings, crank shaft oil seals and piston rings are inexpensive.
Replace all these parts even if inspection finds all clearances
within specification. Remove the rod bearing caps and push the
pistons out through the top of the block. Take care to observe
the orientation of all block parts so they can be replaced as
they were (to help, many parts are numbered or have direction
indicators).
Rod and main bearings are composed
of two C-shaped half sections. Finger pressure on the edge of an
old rod bearing section is usually enough to slip the rod bearing
half section off a piston rod end or a rod bearing cap. Old
piston rings should be removed using ring pliers (tool 3 up).
Unscrew all main bearing bolts and pull off main bearing caps.
Slip out main bearings as you did with the rod bearings. The rear
main bearing cap requires a special pulling tool to remove.
However, I have pulled them by pulling up on the crank with the
overhead "come along" while I tap on the rear main cap
with a rubber mallet. With all the rod and main bearings removed,
the crank shaft can be removed for inspection and for
installation of a new rear main seal.
Clean all parts meticulously
before installation of replacement bearings and rings.
Prelubricate all parts with engine oil plus STP before assembly.
Set all block-side main bearing halves in place then set the
crankshaft back in positionon top of them. Set the other main
bearing halves in the main bearing caps. Place the main bearing
caps with their bearing halves over the crankshaft main journals
to complete the assembly of the block main bearings. Evenly
tighten all the main bolts to the point of contact before you
torque them all to 15 ft-lb and finally to 38 ft-lb.
Use the piston ring pliers to put new rings on a piston
staggering the ring end gaps so the first and second compression
ring gaps do not line up. The 3-piece oil rings can be carefully
slid into the bottom piston ring groove by hand. Place a new rod
bearing half on the piston rod. With a piston ring compressor
(tool 3 left), squeeze the piston rings firmly into their
grooves. Insert the rod and piston into the cylinder they
originally came out of and with the "F" mark on the
piston facing the front of the engine. With the ring compressor
set fully flat to the block surface and tightly squeezing the
rings into their grooves, gently tap the piston into the
cylinder. Be sure the rod bearing sets into the crank shaft
journal as the piston slides into the cylinder. If the piston
does not slide into the cylinder with gentle tapping, do not
force it - tap the piston ring compressor to ensure it is in flat
contact with the block and make sure the ring compressor is
tight. Try again. Repeat this process with the other five
pistons.
For each piston, set and lubricate a new rod bearing half in a
rod bearing cap. Assemble the rod bearings by placing the rod
bearing caps over the crankshaft rod journals and bolt them to
the previously set rods. Tighten to contact at first then torque
down to 10 ft-lb then finally torque to 24 ft-lb. Your block is
rebuilt. You will have high compression and high oil pressure for
the next 100,000 miles.
Engine
Reassembly. Reassemble in the
reverse order of assembly. Modern head gaskets do not require
gasket cement. Before mating the head to the block, rotate the
crank shaft and cam shaft each to the cylinder #1 top dead center
position (crank and cam keyways pointing up). Otherwise, pistons
and valves may clash as the head is placed on the block. Starting
from the center head bolts and working out, tighten all the head
bolts. Finger tighten then torque all the bolts (starting again
from the center) to about 35 ft-lb and finally torque all the
head bolts to 54 ft-lb. Install the timing chain so one silver
link seats next to the mating mark on the crank gear. Install the
timing chain tensioner. Hold the timing chain taut to keep the
chain tensioner in place as the second silver chain link is
seated next to the mating mark on the cam gear (42 links between
mating marks). The cam gear should now fit snugly at the end of
the cam shaft with the cam peg fitting into the number 1 hole of
the cam gear. Torque the camshaft gear bolt to 43 ft-lb.
Press a new front seal into the front cover. This can be done
without a special tool. Grease the seal inside and out. Place the
front cover on a flat surface, set the seal over the mounting
hole with a flat board over it. Hold the board level as you tap
it with a mallet. The idea is to push the seal into the seal
mounting hole with even level force. Apply gasket cement to the
scraped and cleaned gasket surfaces of the block front and front
cover. Install the front cover to the block with gaskets in
between.
Set the engine to TDC piston 1. The oil pump should be replaced,
preferably with a high output pump upgrade. Install the oil
pump/distributor driving spindle and then the oil pump so the
distributor end of the drive spindle can be seen in the
distributor mounting hole with the end slot at 11:25 and the
smaller bow shaped projection facing front. The spindle shifts
about 15 degrees as it is meshes with the crank shaft worm gear
so repeat the oil pump installation until the distributor end of
the spindle is oriented as described above. This is critical to
your ability to set the ignition timing later.
Replace the oil strainer and oil pan using new gaskets and gasket
cement on clean surfaces. Do not over tighten the oil pan bolts
as this warps the seal surface causing oil leaks. Install the
water pump, manifold gasket, manifolds and carburetors. Adjust
the valve clearances cold to 0.007 inches intake and 0.010 inches
exhaust.
Engine Replacement to the Engine
Compartment. Hoist the engine
from the engine stand with the over head "come along".
Replace the flywheel being sure it is well centered before
gradually tightening of the flywheel bolts to 100 ft-lb (for fun,
you figure out how to do this). Install the clutch disk (use a
centering tool to align), pressure plate and throw out bearing
(all new parts is recommended). Lower the rebuilt engine into the
engine compartment. Support the engine on the mounting brackets.
Be aware that the left and right mounting brackets are not
identical; the passenger's side mount having more of an
"elbow". As the engine is lowered it must also slide to
engage the transmission spindle and align with the transmission
bell housing. If it does not slide on easily, the clutch disk may
not be well centered. Use some extra long bolts, such as some
head bolts, instead of the regular transmission blots to
initially align the block and bell housing. When the transmission
fits snug to the block, replace the extra long bolts with the
regular transmission bolts.
With your engine solidly in place, disengage the overhead
support. Replace components such as the distributor, fan,
radiator, pollution control air pump, alternator and starter
motor. Reconnect the exhaust pipe, linkages, wiring and hoses.
Fill the engine with oil and the cooling system with water. After
about 500 miles of driving, replace the oil again.
Contact Gary Baker about protection of your inventions.
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