Most owners of dirt bikes or ATVs rarely encounter a bad head gasket because routine maintenance usually prevents this problem from occurring after completing a top end during normal intervals.
A bad head gasket results in cars and trucks far more often than dirt bikes or ATVs mostly because we tend to neglect our primary use of transportation but keep our toys in tip top shape. Also, ATVs and dirt bikes handle stressful conditions, racing and riding hard much better than automobiles.
However, outside straight-up neglect even the most dedicated garage wrencher can encounter a bad head gasket in the right set of circumstances. So, let's get into it: All the signs, symptoms and what you need to know when the head gasket on your dirt bike or ATV fails.
What Is a Head Gasket?
The head gasket separates the coolant that flows through the cylinder and cylinder head to cool the piston and valve train, on the top end of the engine. In most cases the head gasket is a tin or metal gasket, sometimes several layers thick, with a greased coating to ensure a nice seal when installed.
When Head Gaskets Fail
A failing head gasket allows coolant to pass into the combustion chamber on top of the piston. Since coolant does not compress and burn off (like oil) this leads to erratic operation and possibly damage to the cylinder, piston and crank.
Symptoms of Bad Head Gasket
Symptoms of a bad head gasket include coolant loss, contaminated oil (with coolant), overheating, poor running conditions, poor idle and erratic RPMs. Sometimes the machine won't run at all.
Signs of a Bad Head Gasket
You might see an external leak of coolant with or without poor engine operation but usually the coolant leaks into the cylinder, unnoticed. Well, what about oil leaking into the cylinder? Usually not, thanks to the design of the cylinder head on the dirt bike or ATV.
Therefore, coolant leaked into the cylinder burns off as white smoke out the exhaust and any coolant not expelled out the exhaust works its way past the piston rings into the crank case contaminating the oil turning it milky.
If you notice white smoke or milky oil, you can't just swap out the head gasket and get back to riding. This contamination makes quite the mess and requires several oil changes to clear out the coolant. If you find milky oil, drain it. Don't ride!
In fact, take a day off and let the crankcase drip drain for a while before filling with fresh oil and installing a new oil filter. Run the engine a few times, even a gentle ride, then drain again. (Consider a cheaper oil as a money saver.) If the oil comes out clean change the oil and filter after the next ride.
Hold on though...
Things could get worse. A bad head gasket resulting in a coolant leak into the cylinder can also damage the mating surfaces of the head and cylinder causing warpage. Check both the head and cylinder on a machinist stone or with a straight edge and compare to factory specs. You may also find damaged valvetrain components like valve guides, valve seals, cracked cooling passages and such. You should also inspect the cylinder water jackets and the cylinder walls for cracks.
What Causes a Bad Head Gasket?
Eventually time catches up with you, so not performing a top end or not doing one correctly - both leading to excess cylinder compression among other issues - often results in a blown head gasket. And, any conditions resulting in an overheated engine like riding dunes without the appropriate set-up for the sand or riding at race pace for the length of a Moto in a mudder with a mid-clogged radiator can lead to a blown head gasket. If you continually run into trouble with overheating, especially when riding in sand or mud, an oversized radiator helps. Less expensive options include radiator sleeves or foam.
See what happens when you neglect routine maintenance? For the most part, you can avoid this hassle (and possibly an expensive trip to a mechanic) by following the manufacturer's recommended intervals and not running an overheated engine. A surface mounted temperature gauge lets you know when to shut the engine off if you play in the sand or trying to power through a muddy day.
