Signs Of A Blown Head Gasket On A Dirt Bike

Did the head gasket on your dirt bike just fail? Not sure what a blown head gasket means? This article will cover what a blown head gasket is, the most common signs of one, and how to fix it. 

Fixing a head gasket isn’t that difficult on most bikes. Figuring out why the gasket failed may be the bigger issue, however…

Blown head gasket from CR125

The most common signs of a blown head gasket on a dirt bike are:

  • Overheating
  • Coolant coming out the overflow tube
  • Coolant level lower after riding
  • Low compression
  • Less power

What Is A Blown Head Gasket?

A blown head gasket is when the gasket that seals the cylinder and cylinder head fails. The gasket is either metal or a rubber o-ring. Metal gaskets have a tendency to fail more often than a rubber o-ring. 

What Happens If I Keep Riding With A Blown Head Gasket?

Depending on how bad the gasket is, the result can go from not very good to very bad. The first sign will probably be a loss of coolant. This will either be from it coming out the overflow, or leaking into the cylinder. 

Coolant leaking into the cylinder will burn out the exhaust and have a “sweet” smell to it. 

Continuing to ride with a blown head gasket can and will eventually lead to overheating and seizing the engine if it gets too hot. 

Running Low On Compression?

The head gasket keeps the cylinder sealed to hold the compression. Compression is when the piston comes up in the cylinder and “squeezes” the air and fuel mixtures. A leaking gasket will not be able to contain all of that compression. 

A compression test will show this, and your dirt bike will be down a little bit on power. 

What Causes A Blown Head Gasket?

The most common causes of a blown head gasket on a dirt bike are overheating, a poorly installed gasket, or a gasket failure. 

Keeping your dirt bike at the proper temperature is very important. The more times you boil it over and have coolant spewing out the overflow, the more likely it is to cause bigger problems. 

How To Fix A Blown Head Gasket

A simple replacement of the head gasket can sometimes fix the problem. However, you must get to the root of the problem. 

What exactly caused the head gasket to fail?

Did you simply install it incorrectly, re-use an old gasket, or not properly clean the gasket mating surfaces? If so, then there’s a fair chance that just replacing the gasket will fix your problem. 

You can see the spot where the gasket failed and leaked coolant.

Why Did It Overheat?

Did your bike overheat because the gasket blew? Or did the gasket blow because your bike overheated? Paying close attention to your bike can help you understand foreseeable problems. What do I mean by this?

Something as simple as checking the radiator coolant level before each ride will let you know if your bike has any ongoing symptoms, or if an issue happened during your last ride. 

A low coolant level every time you ride either means you get it too hot and it blows coolant out on your rides, or the head gasket has already failed and it’s burning it up as you ride. 

Overheating Leads To Other Problems

Even well manufactured metals can degrade with too much heat. An overheated engine can cause the cylinder head to warp. 

It won’t be a visual difference, but if you check it with a proper indicator setup, it only takes about a .001 variance to cause issues. A Head that is warped won’t be able to properly seal the combustion of the engine. There is now a small gap where the head gasket is, and that is why it fails. It burns enough of the material away and loses its seal. 

How To Fix A Warped Cylinder Head

This happened on my 2001 Honda CR125 cylinder head. I took the head off and was planning on milling off material to get it completely flat again. However, I was able to use a flat ground piece of steel and out some 320 grit sandpaper on it. I sprayed some oil on the paper to keep it from loading up.

I then rubber the cylinder head on the flat sandpaper. It didn’t take long. I could see where the low spot was after just a few seconds of sanding. I only went until the entire gasket surface fully cleaned up. I’d say it took 1 minute or less for complete clean up. 

Flat sanded a warped cylinder head from Honda CR125
Sanded cylinder head and now it’s ready to go back on.

Wash the cylinder head off with warm water and soap to prevent any of that grit from getting into and damaging the engine when you put it back together.

For tips and instructions on rebuilding a 2 stroke top-end click here.

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