The engine seems to run rough. In the exhaust you can hear an occasion 'poofing' sound like somethings not firing on all cylinders. Under loaded conditions the tractor seems to lack power and it belches black smoke out of the exhaust. For some reason it just doesn't want to start up without cranking and cranking the starter. All these conditions can be signals that your unit is in need of a tune up.

Ok, so what is involved in a tune up? You say, swap plugs and file the points....now that's a tune up! If one wants a tune up that will last there are certain procedures and steps that will breath new life into your engine. It will also give you a very detailed summary for the overall condition of your tractor engine.

First thing to do in a tune up is to warm the tractor up to operating temperature. Then take a can of engine cleaner from the auto store and apply it to the engine area. A small paintbrush will stir up those extra greasy spots and help the solvent dissolve the tough areas of build up. Let the solvent set the required time and then hose the engine off. It's so much nicer to work on a clean engine. Start the engine back up and let it run for around ten minutes. This will warm things back up and evaporate any residual water.

While the engine is drying get a piece of paper and clip board out and make a list of any super greasy spots you saw on the engine that might require a gasket replacement. Look for other causes such as a broken oil line or a leaky pressure sending unit. Walk around the tractor and note any grease build up around rear wheel seals, power unit pumps or hydraulics. Also make note of the condition of the fluid levels: engine oil, radiator, tranny, and/or rear end. Any other observations of the fluids themselves should also be written down, ie: milky engine oil, rusty antifreeze, excessively low levels. Continue with a new section covering the condition of the radiator and cap ( is there any antifreeze leaking from the core, does the cap or core have calcium deposits showing), the hoses (are they hard and brittle, soft and spongy, grease soaked and leaky), and the fan belt (shiny and glazed, cracked and split). Also take note of the general symptoms of any engine problems you encountered (missing on load, hard starting, overheating, just plain runs rotten). Also note the color of the exhaust; blue, black, white or gray. Wipe your finger in the exhaust pipe opening and take note of the residue on your finger; sootie, wet/black, dry black/ gray or brown. These notes will come in very handy.

By now the engine should be dry and you can start the tune up procedure. It may save some frustration if you marked each plug wire with a piece of masking tape and magic marker. Number 1 plug is usually closest to the radiator end of the engine. When removing the plug wires make sure not to jerk on the wire. The internal insulation won't take bending or twisting motion. Instead, grasp the boot at the plug itself and gently pull with a small back and forth twisting motion. If possible take a compressed air gun and blow around each plug base to remove accumulated debris. If no compressed air is available loosen the plugs one or two turns then crank the engine over a few times. The compression will blow away buildup that would otherwise fall into the combustion chamber on plug removal. Next remove the plugs and place them in order on the bench. By doing a visual check on the plugs one can get a quick and simple overview of the engine condition. Plugs that are operating correctly will be clean in appearance. They might have a fine light gray or tan coating on them. The electrode tip may be rounded from long use, and the gap will be above specs. These are all indications of a properly matched and operating plug. It also indicates that the upper portion of the engine; the rings and valves, are all in a good state of wear. Now let's say the plug has a lot of oily black carbon or goo on it. This is an indication of a no fire condition or excess oil in the combustion chamber. A no fire condition can be determined by taking a good spark plug and connecting it to the corresponding plug wire. Use a heavy glove and ground the plug electrode end to the block or other grounded surface. Then crank the engine over for a few turns and see if there is spark at the plug. A no spark condition will be reason to investigate the electical circuitry from the plug on back. If there is a spark on the replacement plug, then install the old plug in the same postion and repeat the process. If the plug does not fire then clean it thoroughly on a wire wheel, reinstall it and try again. If it sparks then further internal engine checks are needed. If it does not fire then the plug is shorted out. Further checks on the engine intergity would also be recommended to isolate the oil buildup problem. A blue exhaust indicates burning oil and is a good indicator of internal engine problems. Further engine tests to determine the oil penetration to the combusiton chamber will be covered under compression testing. Let's continue our discussion on plug appearances.

If the plug is black but dry and fluffy it means there is too much fuel being brought into the combustion chamber or that the installed plugs are not the correct heat range. Perhaps there is too high a fuel level in the carb, a stuck choke or plugged air filter. First check with an auto store to make sure the proper heat range plug is installed in the engine. Heat range is determined by the length of the ceramic insulator from the tip of the electrode to the sealing ring of the plug. This length forms a resistance to the electrical impulse from the distributor and will determine whether or not it fires hot or cold. The longer the insulator the hotter the spark. Too hot a spark will cause detonation in the firing chamber and result in piston and plug erosion. This condition is characterized by bright tan or white glazing on the porcelain insulator. If the heat range is correct and this condition exists that can also be an indication of too lean of a burning mixture. Check for a low float level, too small a carb jet, or a plugged fuel filter or restricted line. Too cold will cause extensive carbon build up and, eventually, misfiring. If the plugs are the correct heat range then check the air filter for excess debris and plugging. The enriched fuel mixture will show up as black exhaust under regular or loaded conditions of the engine. Refer to your inspection chart to verify your engines exhaust color. A stuck choke lever, a carb float set too high, or a stuck needle valve will also cause too much fuel to enter the engine and cause plug fouling. These conditions will be discussed under carburator problems and cures.

With respect to the above, other plug conditions are relatively rare but myriad in number. Scavenger deposits appear as crusty yellowish or whitish buildups on the electrode surface. These result from the chemical makeups of various fuels. Clean the plugs, check the gap and reinstall. Severe detonation, preignition, or over advance ignition timing can leave aluminum deposits from the pistons around the plug electrode. This indicates extensive internal engine damage. Preignition can also severely erode the plug end giving it a melted appearance. If the electrode appears to be dished then check the coil polarity and make sure the wires are attached according to your tractors specs. Squashed electrode ends result from a mismatched plug. The plug is probably too long and the piston has actually hit the end of it.

When installing used or new plugs it is important to check the plug gap. This is the distance between the two electrodes at the base of the plug. If putting in a used plug check the electrodes for cleaness and squareness. A small ignition file should be used to break any oxidation off the ends. Make sure and file the firing surfaces flat with no protruding edges. Take a wire feeler gauge (flat feelers will give an inaccurate reading on older plugs) and set the gap to specs. If no specs are available a rule of thumb would be .035". Make sure and bend the electrode from the side to attain this measurement.

All in all it is important to thoroughly examine the plugs on removal. These little items can give a wealth of information about the internal condition of an engine along with related componets like the carb, ignition system, and air filtering system.

We talked earlier about investigating a high carbon oily goo residue on the spark plug using a compression test. This will help determine the exact cause of the oil buidup. Generally, oil will come in through wore rings, wore valve guides, or worn valve seals (if so equipped). This determination divides the leakage into two catagories; the heads (valve guides), or the bottom part of the engine (the rings). Using a good compression tester one can isolate this location. The tester is, basically, a pressure gauge with a hose on it that screws into the spark plug hole. They are available at many, if not all, automotive parts stores. After warming up the engine, remove the plugs and screw the tester into the first spark plug hole. Disconnect the coil secondary wire at the distributor and ground it on the engine somewhere. Then open the choke and the throttle all the way to provide unrestricted air passage into the intake manifold. Crank the motor over five or six revolutions or until the gauge needle stops rising. Make note of the psi rating on your clipboard. Also note how the needle rises; goes up in jerks, all at once, little at a time. Go on and do the balance of the cylinders recording each reading as you go. Now it's time to examine the readings. If you have access to the pertinent engine manual you can find the psi compression specs in the tune up section. If you can't find the appropriate specs then you need to focus on the continuity between the different cylinders. Generally, a reading between cylinders of no more than 10 psi to 15 psi is permissable. Engine spec compressions may vary anywhere from 80 psi to 150 psi so look for the average on your unit. If three out of four cylinders are around 80 psi and the fourth is real high at 120 psi then one could assume that the firing chamber has an inordinate amount of carbon buildup. As you review your notes observe how the test went for each cylinder. If the needle action came up only a small amount on the first stroke and little more on succeeding strokes, ending up with a very low reading, burned, warped or sticky valves are indicated. A low buildup on the first stroke with a gradual buildup on succeeding strokes, to a moderate reading, can mean worn, stuck or scored rings. If two adjacent cylinders are low, a blown head gasket or warped head to block surface could be responsible. Add a little heavy weight motor oil to the cylinders with low readings and recheck them. If the compression goes up a noticeable amount, worn rings are indicated. If the addition of the oil produces no significant change, valve trouble, a broken piston or a blown gasket may be at fault. If the readings of all cylinders are within reasonably close proximities then one can assume that the upper end of the engine is in good condition.

Spark plug evaluation and compression testing are important parts of an engine evaluation because it will determine if the engine is in adequate condition to do a tune up on. It is a shame to invest in assorted tune up parts only to have the motor still miss and run lousy because a burned valve or broken ring was not diagnosed.

by Curtis Von Fange

In our last episode we spent the entire day checking out the spark plugs. Is that efficency? Actually, it took more time to explain than it really did to do the inspection. At any rate we decided that a compression test was in order so we could verify the internal engine status. That way we wouldn't buy any tune up parts until we were sure that the engine was in reasonable mechanical condition. Our tests showed a fictional compression reading of 85, 80, 82 and 86 psi. That is well within accepted parameters of a 15 psi spread. The spark plugs had a light gray tinge to them and the gap was not excessive. Each one also fired with a sharp bluish white spark when we tested it with each separate tractor plug installed its secondary wire and properly grounded against the block. We decide to clean, regap, and reinstall the plugs as the wear on them was very little. Of course we could have replaced them and not done any of the above, but we're frugal and didn't want to spend unnecessary money.

The next step is to examine the secondary ignition wires; commonly called spark plug wires. These items transmit a high voltage pulse from the distributor to each spark plug. Contrary to popular belief these wires are quite sensitive. Most secondaries have a soft copper core wire surrounded by stainless steel or carbon impregnated thread mixed with an elastomer type conductor. The outside covering of a heavy layer of insulation prevents the 12,000 to 25,000 volts from bleeding out when the wire is carrying current. The resistance type wires do not handle sharp bending or jerking and can break internally thereby ruining the wire. Routing of wires near exhaust systems and high temperature areas can cause the exterior coating to dry out and crack. Excessive exposure to oil and antifreeze can chemically break down the coating causing it to swell and get slippery or slimy. Pulling on the wires to release them from the spark plugs can separate the conducting material causing internal arcing and/or can pull the steel plug connectors off the wire ends leaving them dangling off the plug. Any of these misuses can cause the wires to leak voltage and either misfire to another plug wire, cause carbon tracking in the distributor, cause an intermittent fire at the plug, or no fire at all. Keep them clean and separated from each other with the proper wire clips available at auto stores. When removing the wires from the plugs make sure and grasp the rubber boot, not the wires. Secondary ignition wires have the habit of looking good, but not necessarily being good. They can be the cause of irritating engine 'poofs' that simply can't be located or can make an engine run erratic and backfire. There is a real quick way of identifying bad secondary wires on an engine. Run the engine on a moonless night away from all forms of light. When your eyes get adjusted to the darkness watch the plug wires while on the high idle setting. Bad wires will send eerie flashes of violet light from one plug wire to another. An extremely bad set of wires with moisture on them will give quite the light show. A more sophisticated way, though, is to measure the wire resistance using an ohmeter. A general rule of thumb is 8,000 to 12,000 ohms per foot. This will also test the wire for continuity ensuring that there are no breaks in the copper wire core. An alternative way to check the wires in lieu of an ohmeter is to simply put a test light in series with a voltmeter (or a small 12 volt test light) and the tractor battery. The glowing light or a voltmeter reading the same as the battery indicates continuity of the copper core. A follow up test is to remove the plug wire, start the engine and run a grounded test probe along the plug wire. A wire with a crack or puncture in the insulation will arc a spark to the grounded probe. Replace that wire, it's trouble!

The other end of the secondary ignition wire is installed in the distributor cap. This cap, made of hard plastic or bakelite, distributes the appropriate pulse of voltage to the correct spark plug as determined by the rotor inside. Proper inspection of the cap will reveal hints about the intergrity of the ignition system. Make sure when removing the plug wires from the cap that you grasp and gently twist the boot as you pull. It might be a good idea to label the wires with tape and a magic marker so they reinstall without error. Visually inspect the cap towers. They should be clean and shiny. Many times the secondary wire to the coil will have heavy corrosion in the terminal tower. This causes erratic operation or a no run condition. If corrosion is present replace the cap and secondary wire boots as they are probably cracked or loose and let moisture into the tower. Before wiping the cap off check for carbon tracking along the tower tops to the cap base, usually where the retaining clips are located. Bad plugs or secondaries will cause an occasional or regular spark to occur from any one of the towers to the nearest ground....the mounting clip. The evidence of this happening is a small powderlike carbon trail that resembles a hairlike tree root running from top to bottom of the cap. Replace the cap if this is present. Now turn the cap over and inspect the inside. Check the center carbon terminal and the individual terminal posts for cracking or burning. Carbon tracking on the inside will look similar to outside except that the hairline fracture lines will run from terminal post to post; evidence of cross-firing, backfiring, or missing. If the posts are burned or grooved the cap should be replaced. Mild scaling, caused from the spark leaping from the rotor to the post, can be scratched off with a sharp object. Try not to groove the terminals as they are probably made from aluminum and are quite soft. When replacing the cap it is best to replace the rotor also. If reusing, gently scratch the rotor prong so as to remove any oxidation or scaling.

The ignition points act as a switch to open and close the primary ignition circuit. When the points are closed, current flows through the ignition coil and builds up a magnetic field. When the points are opened, current through the coil is stopped and the magnetic field collapses, creating a high voltage current. Sound simple? It is if you understand how electricity works. But we're only interested in getting the points set correctly so we won't worry about how it works...just as long as it works. But first, let's take a closer look at the distributor itself.

It's easier to clean and inspect the distributor if it is removed and put in a vise on the workbench. It is understandable, though, if one doesn't feel comfortable pulling this rotating heart from engine. Getting it reinstalled and timed correctly can be a hair pulling experience if you've not done it a few times. But for those of you who are adventurous, I'll walk you through it. In order to save reinstallation time set the distributor cap back on the unit and take note where number one plug wire tower is. Mark the distributor housing side with a chalk mark that corresponds to this tower. Pull the cap back off and note where the rotor firing prong is. Rotate the motor by hand (it's easy without the plugs in) so the rotor prong lines up with the chalk mark (also note the rotor rotation direction). You might note that when they align, the timing marks on the crankshaft pully will line up with the timing cover arrow. This means that number one piston is at top dead center on the compression stroke and the distributor is firing on that spark plug terminal. Also note that the points are just opening....you can tell because a high spot on the rotating cam on the d-shaft has pushed against the rubbing block at the point base forcing the points to separate creating a gap. When the spark jumps the gap it causes the coil to fire the high voltage spark to the cap rotor and from there to the correct cylinder. With the motor timed to number one you can now remove the mounting bolt and fork that retains the distributor in the motor housing. Observe how the rotor shaft will rotate a little as you remove the distributor. This is because the drive gears are usually tapered and as you pull up on the distributor the unmeshing of the gears causes the shaft to turn. Remember when you reinstall the shaft you will need to be off center to the mark you made by a little to compensate for this gear taper. Make sure and disconnect the battery ground cable so the kid doesn't roll the engine over while you're working at the bench. If you forget, and he does, don't dispair. You can retime the engine by placing your finger over number one spark plug hole, then roll the motor over so you feel compression trying to blow your finger off. Jockey the crank to align the timing marks back up and this will be top dead center (TDC) for number one piston. When putting the distributor back into the bore align the rotor tang with the mark on the distributor casing that you made....make sure to offset the rotor a little to compensate for the gear mesh.....and slide it in. Some engines have a tang at the bottom of the d-shaft which runs the oil pump. Make sure this tang engages the pump shaft. If it doesn't then put a little downward pressure on the shaft and then rotate the engine a quarter or half turn. The shaft will then drop into postion.

Now that the distributor is in the vise observe the inside condition. Is it clean or is it full of oil, dirt, or carbon debris? If there is oil in it then the bushing or seal at the bottom of the distributor is bad and needs to be replaced. Wobbly motion of the shaft in the housing bore will confirm this. Excess carbon indicates the points have been arcing too much or there has been a lot of cross firing under the cap. Dirt and debris can be caused from an opening in the side of the cap and/or a dry rubbing block at the base of the points. A little bit of high temperature grease on the block facing the cam rotation will reduce that problem. Remove the points and condenser and set aside. Underneath the mounting plate there may be a spark advance system of springs and counterweights. Make sure they freely rotate and that the springs aren't broken. Moisture buildup tends to rust these gizmos up a lot so you may have to break the distributor down a little farther to get to them. Take note of the proper order as you disassemble. The configuration may look a little different on the bench as it looked in the unit. Wire brush and clean the pieces in solvent before reassembling. Some newer tractors may have a vacuum advance diaphram. Make sure the rotating linkages are free to move and check the diaphram by sucking on the vacuum port. The vacuum plate will rotate as pressure decreases. Hold the pressure on with your tongue for a few seconds to see if the diaphram has any small cracks in it. Now lets check the points. If the points are a dull slate color and if wear is not excessive they can be cleaned with a point file and reinstalled. Don't use sandpaper or emery cloth as this will scratch the point surface and leave small grit particles imbedded in the points. Use a clean file as this will remove a small layer of metal creating a good flat surface to fire against. If the points are burned or pitted they need to be replaced. If one side of the points is severely pitted and the other side has metal buildup on it then you need to check and make sure the correct capacitor (or condensor) is installed. Also check the coil polarity. Most engines have a wire running from the negative terminal of the coil to the distributor. It is common practice to replace the condensor when the points are replaced. A leaky one can cause excessive point arcing and/or metal transfer on the point surfaces. Reinstall the refurbished or new point set in the distributor. Rotate the shaft so the cam lobe separates the points, creating a gap, and measure the gap opening with a wire type feeler gauge. Set to specs and tighten the mounting screws. Make sure and keep the rubbing block lubricated with a small dab of high temperature grease. Install a new rotor, line up the casing marks and reinstall the distributor in the housing....don't forget to compensate for the tapered gears. The mark on the distributor casing should now line up with the rotor tang. If it doesn't then you are probably off one tooth. Pull it out and reinstall it again. The plug firing order is usually stamped somewhere on the engine block. Locate it there or in the manual and reinstall the plug wires accordingly. You know where number one plug is on the cap and you wrote down the d-shaft rotation, so install the wires in their respective order and attach them to the corresponding plug. With the current distributor alignment the tractor should start and run. Additional timing should be checked and adjusted with a timing light. Attach the light pickup to number one plug wire, start the engine, and aim the light on the crankshaft pully timing marks. Adjust the distributor according to specs. If no light is available then you can static time the engine. It won't be as close a timing light but it will be next best. Look in the book to determine the exact firing timing for that motor. Most of them are 4 or 6 degrees before TDC. Rotate the timing mark on the crank pully to line up with the housing cover arrow according to the specs. Hook up a spark plug to the number one secondary wire and hold it against a ground. With the ignition on, rotate the distributor in the direction of normal distibutor rotation and watch for the exact moment that a spark occurs at the plug. If it caught you by surprise back the distributor up and do it again. The engine is now timed properly. Tighten the distributor mounting bolt and secure all the necessary wires.

One last thing to check in this section is the integrity of the primary wires running to the coil and distributor. Check to see that they are securely fastened and have no exposed strands from broken or crimped insulation. The coil should be clean and dry; check the termial tower for oil or corrosion. If oil is present it indicates internal leakage and the coil should be replaced.

Now that we've slapped new plugs and points in we'll go on, in our next segment, and look at filters, hoses, and belts.

by Curtis Von Fange