What are the signs of motorbike engine problems and how do I troubleshoot them?
A motorcycle is a machine just like any other and needs maintenance to keep it running smoothly, but just like any machine, it is subject to mechanical failure. If you suspect an issue from your bike we can help! It is also very helpful if you cannot fix it yourself so you are able to describe the problem to a technician.
Fault Finding
The first sign of an engine problem is the dashboard lighting up with a warning of some type and then usually followed by difficulty or failure to start the bike. You may also experience a loss of power or knocking sounds from the engine while riding. An engine needs three things to run, namely, fuel, compression and spark; following the pathways after each of these things may help you diagnose a problem. It goes without saying that if the engine won't turn over at all and is seized up, none of the below troubleshooting will tell you anything.
Telltale signs of electrical issues will see the bike cut on and off while applying the accelerator, fuelling issues will cause similar issues with the engine breaking up at higher RPMs, while compression issues are usually accompanied by starting issues and loss of power. If the engine is a non-starter but turns over, you can follow the below troubleshooting guide, but without a starter and a fresh battery, you will be dead in the water.
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Spark
The motorcycle's electrical system has a number of systems that work hand in hand to ensure the engine runs. There will be a crank trigger in the form of a sensor or magneto that picks up a signal from the turning crank that will tell the electrical system to fire the sparkplugs in sequence. If you pull one of the sparkplug leads, place a screwdriver inside and hold the barrel of the screwdriver close to the engine and swing the starter, you should see a small spark jump between the two. If there is no spark, then you have found your issue, and its time to follow the trail.
You will need a multimeter to continue as you will need to measure the voltage output of the crank trigger or sensor. If no signal is detected then you have found the problem. If you have a crank signal, then you will need to dig deeper into the electrical system but it is highly unlikely that the problem will go deeper than a broken wire or earth problem. If you have gone as deep as you can and find no issues, you will need to move on to the next check.
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Compression
If the engine will not start and seems to be turning over too easily, there may be a lack of compressions inside the cylinders. This could be due to worn-out cam shims, worn piston rings or a blown head gasket. The only way to properly test this is with a compression tester. You will need to remove each spark plug one at a time in sequence and do a compression test on each cylinder. The compression tester screws into teh sparkplug hole and will take a compression reading. Some light reading will be required to determine what the manufacturer's reading should be. If one of the readings is way off or if the tester is not responding at all, you have found your problem.
The cylinder giving the incorrect reading will need to be further examined, and this is where a boroscope will be required. A boroscope is a small camera at the end of a long flexible shaft that can be inserted inside the cylinder through the sparkplug hole and then the piston, cylinder bore and possibly the underside of the head and valves can be examined.
A blown head gasket will be accompanied by different-coloured smoke from the exhaust and significant overheating, so keep an eye out for that. Worn cam shims will be accompanied by rattling noise from the engine and loss of power can be attributed to badly worn piston rings.
If the readings are all balanced and you don't hear or see any of the other telltale signs of compression-related issues, you will need to check your fuel next.
Fuel
This should be the first port of call when it comes to any troubleshooting. It is extremely common for folks to just forget about how much fuel they have in their tank. Always check your fuel level in the tank before doing any troubleshooting. With no fuel to combust, the engine wont run, so always start here.
Troubleshooting a fuel issue is a lot more difficult today as newer bikes use fuel injection and fuel pumps, and these systems are sealed and inaccessible. If your bike still uses carburetters, the fuel lines are accessible and unpressurised, and you can usually pull these to see if there is fuel present. On these older bikes the lack of compression very often affects the fuel system as there is a certain amount of vacuum created that draws fuel through the carbs.
A telltale sign that fuel is not the issue is if you have been swinging the engine over for a while and there is a pungent smell of fuel in the air. This means that fuel is being pushed into the cylinders but is not combusting, and you can assume either an electrical or compression issue.
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Finally
There is one more suspect but it is highly unlikely if the engine is or was running. This is timing; the cam/crank/ignition timing may be out, most likely caused by a slipped timing chain or belt, but this is something that is very difficult to diagnose without tearing the engine apart, so it should be your last port of call in your diagnosis. If at any time you are overwhelmed or don't feel comfortable with the tasks or if the bike is still under warranty, DO NOT mess with things and just take it to your nearest approved bike workshop and have them fix it.
