Get Your Motor Runnin!

If your are trying to get a motor started, any motor, in any car, remember: fuel, compression, spark.  These are the very basics, but they are the starting point.  First of all ensure that you have each of these things, then if the motor still does not want to run, grab a coffee and put your coveralls on, because there is something else wrong.

  1. First thing, check for fuel.  It is oftentimes easier to check for fuel by verifying its absence.  Dribbling a couple of drops of gasoline down any carburetor will usually provide enough fuel for the engine to run for a few seconds.  If it does this, you know that something in the fuel delivery system is not working.  I have a little advice for you guys out there, but I know that most likely it will go unused.  When attempting to dribble gasoline down a carburetor (or prime a motor), most guys will just pour some gasoline into a small can or a jar and dribble the gas in from there.  The danger here is from backfires, which occur frequently when fiddling with motors that don’t seem to want to start.  So if you have just poured some gasoline down a carburetor and it backfires out the carb, it can light your little can of gasoline on fire and possibly you with it.  Try using some sort of squirt bottle, an old water bottle, anything where the gasoline is not exposed to the air.  I would recommend a turkey baster here if you promise not to tell your wife it was me who mentioned it.
  2.  The next thing to check for is spark.  This is simple enough.  Pull one of the spark plug wires off at the spark plug, insert a Robertson screwdriver into the socket and hold the screwdriver a 1/8 of an inch away from any ground on the vehicle.  You should easily be able to see the spark jumping from the expose metal of the screwdriver to the ground, if you don’t, there is an ignition problem.  I must admit that I have shocked myself dozens of times when attempting the procedure I just outlined.  If you have an old spark plug wire, cut the boot off one end and use it to test for spark as it is much easier to avoid getting electrocuted.
  3. The last and most difficult test is for compression.  This test usually takes quite a bit of time and requires a compression gauge.  These gauges are fairly inexpensive and can sometimes be rented from auto parts stores.  If you are buying a compression tester, I recommend the thread-in variety.  Some compression testers have a rubber cone on the end that is supposed to be pressed into the spark plug hole.  I have found that these units are hard to get a good seal with when the spark pug hole is hard to reach.  At any rate, I am going to continue discussing compression testing in the next section.


Here are a couple more important notes about engines:


Test for compression.  Compression is the most definitive measure of an engine’s functionality and power.  In essence, the compression is where all the power and force of an engine is coming from, so the more compression, the more power.  However, before we go too far, it is important to know that a motor’s functionality, that is it’s ability to run smoothly and operate consistently, is based on having balanced compression in all the cylinders.  So if you are testing out a used motor to see if it is will run, look for all the cylinders to have equal compression.  No more than ten or fifteen psi difference between cylinders.  If you find a cylinder with no compression, then there is likely a valve stuck open.  If you are testing to make sure a high horsepower engine is actually high horsepower, you will be looking for high compression 120 psi or higher and utterly equal between cylinders (maximum 5 psi difference)


No other single part will improve the operation of an engine more than replacing a worn timing chain.  Remember when we covered camshafts and how they were the “brain” of a motor?  Well the timing chain in most older v-8 engines mechanically links the rotation of the crankshaft to the camshaft.  So, in essence, the timing chain (or timing gears in some cases) is responsible for making the brain of the engine function.  As a timing chain wears out and becomes loose, the camshaft may not be in exactly the right position in relation to where the crankshaft and pistons are.  In fact, if a timing chain becomes really worn it can even skip a tooth on the crankshaft gear and render a motor completely useless.  Not permanently, but a motor will not run even for a second with the timing chain one notch off the correct alignment.  So anytime you are working with a used engine, or if you are trying to get a stock motor to fire up, check the timing chain.  Timing chains are cheap compared with most other engine components and replacing a worn unit is not only beneficial, but oftentimes essential to allow for proper tuning.  I will go one step further here and step outside the hot rod environment as I think that the following information is of the utmost importance.  In any newer overhead cam engine (almost all engines nowadays) but certainly in all imported vehicles manufactured after 1980, the camshaft is most likely driven by a belt.  The benefit of a belt-driven timing system is that they almost always have automatic slack adjustment.  This eliminates the problem of misalignment as with worn out timing chains.  The problem is that timing belts tend to simply break completely when they wear out.  And here is the important part.  When a timing belt breaks, usually the camshaft and valves stop moving immediately, but the crankshaft and pistons usually have enough momentum to complete a couple of revolutions before they come to rest.  The problem is that most imported vehicles have engines that are built in such a way that an open valve will actually contact or interfere with a piston at the top of its stroke.  So when the timing belt breaks, the pistons smash into all the open valves and bent the valve stems, essentially destroying all the valves.  This event usually requires the head to be rebuilt at a very significant cost to the owner.  The lesson here: if you only do one piece of maintenance on your import vehicle, change the timing belt.  Having a timing belt changed can be a costly repair as well, but it is never as much as having to rebuild a head.

 So, hopefully these few pieces of advice might help you get your hot rod fired up.  If you find more extensive problems, there are probably solutions in other sections of this blog that might help.  If you have some other neat tricks when working on engines, please leave us a comment, we’d love to hear from you.

And remember to tell your friends about us.