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Tailgate troubleshooting.

There you are, two miles back of beyond, and your chainsaw has sputtered and died just as you dropped her in the cut. I know firsthand the frustration that comes from a balky saw, but a trip to the shop or the dealer may be avoidable. The secret of repairing a chainsaw anywhere, and especially in the woods, is an understanding of how your saw works.

In theory, the saw utilizes three systems that must all work together. Fuel, electrical, and mechanical components need to perform satisfactorily in proper synchronization, and therein lies the first clue to successful stump-top problem solving. The first job is to determine which system has failed.

Once that is done, you've taken a major step toward putting your saw back in operating order. All topnotch mechanics are above average detectives. A problem can't be fixed until it's found.

One note before we continue. Keep in mind that I'll be purposely bypassing simplistic oversights such as an empty fuel tank, an improperly adjusted choke, or a switch in the Off position. For the remainder of this article, I'm assuming that you are a competent operator who has read the manufacturer's instructions and is following them. The problem is not that you don't know how to operate your saw but rather that you aren't sure how to go about repairing it.

Suppose the saw doesn't start despite vigorous effort on your part. The problem is apt to lie with either the fuel or electrical system, not the mechanical components. Repair clue No. 2 is always to check the easiest items first. To me that means the spark, so here goes.

Start by removing the sparkplug and examining it for bits of carbon bridging the gap between the electrodes. Carbon particles prevent ignition by allowing the current to flow from electrode to electrode without having to arc. Also examine the plug for damage. If the porcelain is cracked, the current can exit to ground and will not ignite the fuel/air mixture.

A sparkplug with cracked or broken insulation is useless. Take it home and dispose of it properly. But a carbon-incapacitated plug can often be returned to use after the carbon has been carefully scraped away with some thin tool like the blade of a pocketknife.

Suppose the plug still won't fire, so you've tried a new plug with the same results. What next? Disconnect the On/Off switch from its wire, and place the wire terminal so that it will not be near any metal surface and thus complete the electrical circuit. (With chainsaws, the On switch breaks the circuit and lets you start the saw, contrary to the way the ignition switch works on a car.) If a retest of your plug produces a spark, the switch is defective and must be replaced. However, this doesn't necessarily dictate an immediate trip to your dealer. You can finish the day with that saw, but you will have to choke it to stop it, and restarting may take a bit longer due to the resultant flooding.

Intermittent spark can result when the ignition wire no longer makes a solid contact with the gripping terminal located inside the sparkplug boot. These terminals are of varying design, but this problem can usually be remedied on the spot by reassembling the components, which is often enough to get a tighter fit.

Occasionally, a plug will show spark when tested but will not ignite the fuel mixture. The compressed atmosphere within the firing chamber makes life a bit more difficult for the ignition system because a stronger current is required to arc across a sparkplug's gap under those conditions. Attempting to operate the saw with a spare plug is the remedial method for this situation. If the saw runs with the spare plug, use the spare and get rid of the weak original plug.

Three tips for spark arc testing. Note the color of the spark-blue is preferred over orange. Did the spark appear tentative, or was it sharp and crisp? And finally, how slow can you pull the starter rope and still get a good, reliable spark? The slower, the better.

If the sparkplug seems to be working properly, the next thing to check is the fuel system. Remove the sparkplug from the cylinder to see whether the plug is damp. A moist plug indicates that fuel is getting to the firing chamber. Another way to test for fuel movement is to turn the switch off, pull the choke on, place your thumb over the sparkplug hole, and pull the starter rope several times. Your thumb should get wet if the fuel system is functioning properly.

A few words of caution might be appropriate at this time. Always provide a ground for the electrical current generated when the ignition system is manually activated by pulling the starter rope. This can be done by either grounding the plug on the engine or flipping the switch off. Failure to do so can damage the saw's electrical system.

Sooner or later all saws require a bit of carburetor adjustment. Manuals are usually straightforward as to how this is done, so I'll just touch on what to listen for. The saw should idle as fast as possible without the chain moving, and accelerate without hesitation when the throttle is squeezed.

Use your ear to guide hi-jet adjustment by listening to what your saw is telling you. Open or turn out the high-speed jet until the saw starts to four-cycle or "blubber" while at full throttle with no load. Do not hold the throttle at full speed for more than a second or two as engine damage can occur when the saw is not actually cutting. Instead, bring up the engine speed, make an adjustment, and let the saw drop back to an idle, repeating these steps until you've got it right.

Now turn the hi-jet in, usually only a fraction of a turn, until the exhaust tone loses its blubbering sound and levels out. Stop at that point! Don't succumb to the temptation to turn the hi-jet in until the saw "screams." People who do so don't understand chainsaws. They're asking for higher performance with less lubrication-and trouble.

The fuel supply can be interrupted in several ways, most of which are easy to check. Dirt can be the culprit, accumulating in the tank or on the filter, blocking the air flow through the fuel-tank breather, or restricting fuel flow by lodging in the carburetor orifices. The filter and breather can be readily inspected in the woods. Replacing the filter and cleaning the breather are the appropriate responses. Dirt that has found its way into the carburetor is best removed in the shop, where cleanliness is better assured and compressed air is available.

A carburetor that has become loose will definitely prevent the saw from running. A new gasket and/or sealant may be in order, but have a go at tightening the mounting bolts. You might be able to get by for the moment.

Don't overlook the fuel line itself, as pinholes and tears can develop. The junction of the fuel line and carburetor is the most likely location for a tear. If the line is long enough, simply cut off the defective end and reconnect. Be certain that doing so does not place excessive strain on the hose or cause it to kink.

Some saws have an exposed bar-oil line that is located behind the clutch. Should this line become dislodged, you might be able to reconnect it with a needle-nose pliers. In most cases doing so will require that the clutch be removed to make access possible.

The clutch will be held on by a left-hand threaded nut that may or may not be an integral part of the clutch. The most common way of holding the crankshaft is to block piston travel by inserting an object into either the sparkplug hole or the exhaust port. Threaded piston stops are round in shape, metallic in composition, and are the only metal objects that should ever be used as piston stops. They are of differing dimensions, so make certain that you have the correct stop.

Exhaust-port stops, which are wedges of a non-metallic material, are much simpler in design. Use of these stops requires that the muffler be removed. At this point, my description of the procedure gets a bit lengthy, so please follow carefully.

The muffler is removed and you're ready to put the exhaust-port stop in place. Before you do, pull all the rope out of the starter and tie it on the wrap-around handle. (I'll explain why later.) Now turn the clutch clockwise with your wrench until the piston drops and the port is open. Insert the stop and resume applying clockwise torque. Clutches can be stubborn, so be prepared to use some muscle. And try not to skin your knuckles on the bar studs.

When the repair is completed, you will have to turn the clutch counterclockwise to reinstall it, but you'll find that when you do, the piston stop isn't working at all because the starter ratchets have engaged. Untie the starter rope and allow it to rewind by turning the clutch, which will rewind the first segment of rope. After the piston has completed the bottom portion of its cycle and is snugly up against the stop, you may gently allow the remainder of the rope to rewind. Following this procedure will prevent damage to the starter component. Torque the clutch to the manufacturer's recommendations, and you're done.

Two other items are commonly substituted for commercial piston stops, and although they do work, certain words of caution are in order. A piece of wood can be inserted through the exhaust port, but make certain you remove all fragments should splintering occur.

Spare starter rope can also be used through either the sparkplug hole or the exhaust port, but be aware that there is a right and wrong method. Double the rope over and grasp both ends while stuffing the remainder of the rope into the cylinder. Should the rope become severed, you will be alerted because two pieces will emerge. You must then be absolutely certain that no rope remains in the cylinder. Failure to do so could result in a big-bucks repair.

Starter ropes can break from normal use and will usually do so on the handle end. Repair takes but a few moments and can be done on the spot. Detach the starter assembly from the body of the saw, rethread the rope through the housing and handle, tie the knot recommended by the manufacturer, and reset the tension by using the rope to turn the rewind drum. Continue by carefully allowing the spring to rewind the rope, and you're ready to reinstall the starter assembly.

When the oil holes in the bar become plugged, they can be opened with a bar-groove cleaning tool. I use the tool that comes with the saw, but practically anything thin enough and strong enough can work. If it turns out that the oil holes are not filled with foreign matter, your oil pump may need attention. Usually, repair of an oil pump requires a trip to the shop, but there are times when you'll want to determine if the pump is putting out oil.

Most oil pumps are driven mechanically, being activated by movement of the clutch drum or crankshaft-mounted gears. The engine must be running to test the performance of an automatic oil pump. The following advice is important and should be followed exactly. Remove the clutch guard, bar, and chain. Start the saw, but don't set the fast idle latch and don't rev the engine. To do so is unnecessary and could cause the clutch to come off the crankshaft.

A dealer I used to know gunned a saw while testing the oil pump. The clutch left the crankshaft, twirling madly. It crossed a parking lot, a lawn, a ditch, and a state highway, and finally came to rest on the far side of the road. Thankfully, no person or object crossed the clutch's path.

If your saw has a clutch-activated oil pump, you will have to bring up speed until the clutch drum is engaged, but do so carefully and let it down gently while ensuring that no one is in a potentially dangerous position.

One more thing to check is the oil-flow adjustment screw. Usually, this can be done while conducting the oil-pump test, and the results of the screw adjustment can be readily monitored.

Abnormal bar and chain problems can frequently be remedied in the woods. If the chain leaves the bar and the result is that the drive links become burred, simply hold the chain so that the affected links protrude. Now remove the burrs, preferably with a flat file, but a round one will do.

Pinched bar rails can be re-spread by driving a screwdriver between them. A bent bar can sometimes be straightened by flexing it across the bumper of a pickup truck or similar solid base. Although these remedies are not the ideal, they can allow you to finish the immediate task at hand.

To doctor a chainsaw in the deep woods, you need to carry along a basic assortment of tools and spare parts. In addition to those described below, I pack a screw assortment, a bar wrench for each different size of saw that I own, a six-inch flat file, a fuel filter, and a depth gauge file guide. For spare chains I have a military-surplus ammo box that contains about two inches of bar oil to keep the chains constantly immersed and protected against rust and corrosion.

Take a tip from one who knows. Sharpen your chains before you put them in the oil bath. That way they will be ready, saving you time and the aggravation of filing a chain laden with oil.

This brief set of tips is by no means all-inclusive. Despite my years with chainsaws, I'm convinced that I have not seen all the breakdown tricks a chainsaw can pull. But at the same time, I'm not afraid of the unknown.

A chainsaw is a complex tool that is subject to occasional failure. Find the problem, and you can fix it. Understanding the chainsaw's triangle of electrical, mechanical, and fuel systems allows you to isolate the problem's source from its symptoms, and then make the appropriate repairs. Downtime is costly whether you're a pro logger or a weekend woodsman, so don't waste woods time with needless trips to the repair shop.

The Tool Kit

To be a deep-woods saw doctor, your basic tool assortment should include a chain-repair tool, 4 min allen wrench, 5 mm allen wrench, flat file, 7/32 round file, 3/16 round file, 5/32 round file, 13-21 mm combination wrench-scrcwdriver, 19-21 mm combination wrench-screwdriver, bent-jaw needle-nose pliers; saw-chain repair parts, spare sparkplug, universal piston stop, carburetor screwdriver with built-in magnet, bar-groove cleaning tool, raker filing gauge, spare screw assortment; sparkplug gap gauge, spare starter rope.
COPYRIGHT 1989 American Forests
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1989, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
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Title Annotation:repairing a chainsaw
Author:Boness, Kenneth R.
Publication:American Forests
Date:Sep 1, 1989
Previous Article:Journey to the bottom of a tree.
Next Article:Vine maple autumn.

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