Is The Motor Any Good On That New Project? -
A Step by Step Guide to Diagnosing Engine
By Tom Rahm
You gave up that stack of Benjamins, and got a cool project to rescue
from The Crusher. Now it's time to see what you really have.
Assuming you have a fresh battery and a starter that turns the engine
we can begin.
Engines need three elements to run: Fuel, spark and compression.
Check for spark first. Pull any spark plug wire off of the distributor and
spin the engine. It should arc a healthy spark when held within an inch
of the connection at the distributor. If it doesn't arc, it has ignition
woes. Pull the distributor cap off and check the rotor/points to see if
everything rotates when the engine cranks. It's common on old cars
for wires to break or corrode, if it still doesn't spark after checking the
connections it probably needs a coil.
Be sure the carb has fuel, or just squirt starting fluid in to be sure it
has enough fuel to start after you verify spark. It should fire or at least
partially fire at this point. This is assuming you have the plug wires
Check The Compression:
You need a compression gauge for this. They're only about $20.
Remove all spark plugs and start with the number 1 hole and turn the
engine 7-10 times to get a good reading. Healthy numbers should be
140 to 150 lbs. The numbers can be much higher on high
compression engines, 180 plus is common on those. The important
point in compression readings is to have even readings among all
cylinders. They should all be within 5 lbs of each other. If one cylinder
is 15% or more under the others, it's time to do a Wet Compression
Wet Compression Test:
Squirt about 1/2 teaspoon of oil into the cylinder, then take another
reading. This has a sealing effect on the piston rings and cylinder. If
the compression numbers increase with this sealing effect, it's likely
worn piston rings/cylinder scoring. If the numbers stay low it's likely a
leaky valve. A machine shop can grind a valve seat for $80 - $100.
Worn rings require complete engine disassembly/rebuild.
Adequate oil pressure is about 10 lbs for every 1000 rpm. It's not
unusual for some engines to have 5 lbs or less at idle. This isn't as
big a problem as it may seem, but you DO need to keep the oil level
up to prevent bearing damage. Don't let the oil level get low!! If you're
not going to beat the car down a drag strip, these low numbers which
are common on worn engines isn't a problem generally.
Timing Chain Inspection:
Remove the distributor cap to expose the rotor, and rock harmonic
balancer back and forth with a socket/breaker bar. Excessive play
should be clearly visible. This of course indicates a worn timing chain.
The engine will still run with quite a bit of play, but performance will
drop proportionally to the excess play.
Pull the valve covers off and simply watch the rockers in motion at
idle. A flat tappet will be fairly obvious. This isn't an emergency
usually, but it's good to know the vitals and this is easy to check.
To inspect rocker motion while the engine is running, it's handy to
have an old pair of valve covers to cut up. Cut the top face off to
leave the base and sides, then bolt into place on the head, and you'll
have a valve cover with a big window to view the rockers. This keeps
oil from running out and making a mess.
Disconnect the vacuum advance and hit the timing mark with the
timing light. A good setting is 8-10 degrees before top dead center
(BTDC). To adjust timing, loosen the distributor clamp and simply
rotate the distributor accordingly.
These can be most easily checked by listening to the way the throttle
transitions from open throttle to idle. If the engine stays at a high rpm
after the throttle is closed to idle position, it's usually because the
engine is sucking air through an air leak in the intake tract. If the car
won't idle at a steady rpm this can also be the cause. If the car
backfires when the throttle is opened, it can be a phasing problem
between the vacuum/mechanical advance and the unmonitored intake
charge through the vacuum leak. These are some symptoms of
vacuum problems. Of course to remedy these problems, be sure the
gaskets and vacuum hoses in the intake system are sealed.
These basic tests will give you a good idea about the health of your
Article Source: http://EzineArticles.com/?expert=Tom_Rahm