I turn key and starter spin but will not engage flywheel.
You have one of two problems: Either the starter
drive on your starter is defective and is not engaging the flywheel
to crank the engine, or the flywheel has some broken or damaged
teeth that are preventing the starter from engaging.
Starters come in a variety of designs. On some, the solenoid
is mounted on top of the starter. When you turn the key, the
solenoid routes current to the starter motor and at the same time
pulls a lever that slides the drive gear mechanism out so it will
engage the flywheel and crank the engine. If the solenoid is
weak or damaged, it may not be strong enough to overcome the spring
tension that retracts the drive gear. So the starter spins but
doesn't crank the engine.
On other starters, the solenoid is mounted remotely. When
the starter motor starts to spin, it ratchets out so the drive
gear will engage the flywheel and crank the engine. If the drive
mechanism is damaged or hung up, the motor may spin but not crank
the engine.
Regardless of what type of starter you have, it will have
to come out for further inspection. The drive gear (which is
sometimes referred to as a "Bendix drive") should move
out when the starter starts to spin. The drive gear usually has
a one-way clutch that is supposed to protect the starter against
damage if someone keeps cranking the engine once it starts. The
gear should turn one way but not the other. If the gear is locked
up or turns freely either way, the drive is bad and needs to be
replaced. If the drive can't be replaced separately, you'll have
to replace the entire starter.
Starter Testing
If the drive seems okay, the starter should be "bench
tested" using jumper cables or special equipment designed
for this purpose.
CAUTION: Be careful because a starter develops a lot of torque.
It should be held down with a strap or clamped in a vice (be
careful not to crush or deform the housing!) before voltage is
applied.
A simple no-load bench test can be performed with a battery
and a pair of jumper cables to see if a starter motor will spin.
But this test alone won't tell you if the starter is good or
bad because a weak starter that lacks sufficient power to crank
an engine at the proper speed (usually a minimum of 250 to 500
rpm) may still spin up to several thousand rpm when voltage is
applied with no load.
A better method of determining a starter's condition is to
have it tested on equipment that measures the starter's "amp
draw." A good starter should normally draw a current of
60 to 150 amps, depending on the size or power rating of the starter.
Some "high torque" GM starters may draw up to 250 amps,
so refer to the OEM specifications to make sure the amp draw is
within the acceptable range.
If the starter does not spin freely, or draws an unusually
high or low number of amps, it is defective and replacement is
required.
An unusually high current draw and low free turning speed
typically indicate a shorted armature, grounded armature or field
coils, or excessive friction within the starter itself (dirty,
worn or binding bearings or bushings, a bent armature shaft or
contact between the armature and field coils). The magnets in
permanent magnet starters can sometimes break or separate from
the housing and drag against the armature.
A starter that does not turn and draws a high current may
have a ground in the terminal or field coils, or a frozen armature.
Failure to spin and zero current draw indicates an open field
circuit, open armature coils, defective brushes or a defective
solenoid.
Low free turning speed combined with a low current draw indicates
high internal resistance (bad connections, bad brushes, open field
coils or armature windings).
the new radiator into the support and replace the support screws and nuts. Reattach the hoses and wires in reverse order.
