6 DEADLY Indicators of A Grime Bike Blown Head Gasket & Why

Did the top gasket in your dust bike simply fail? Unsure what a blown head gasket means? This text will cowl what a blown head gasket is, the commonest indicators of 1, and repair it. 

Fixing a head gasket isn’t that troublesome on most bikes. Determining why the gasket failed stands out as the larger problem, nevertheless…

Honda CR125 Cylinder head with a blown head gasket
Blown head gasket from CR125

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 both metallic or a rubber o-ring. Steel gaskets tend to fail extra usually than a rubber o-ring. 

What Occurs If I Maintain Using With A Blown Head Gasket?

Relying on how unhealthy the gasket is, the outcome can go from not excellent to very unhealthy. The primary signal will most likely be a lack of coolant. This may both be from it popping out the overflow, or leaking into the cylinder. 

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

Persevering with to experience with a blown head gasket can and can finally result in overheating and seizing the engine if it will get too sizzling. 

Lethal indicators of a blown head gasket on a mud bike

Whether or not you could have a mud bike, motorbike, or automotive, the signs of a blown head gasket are typically the identical. A standard mistake is seeing or feeling these signs, however not doing something about them till it’s too late – that’s when you could have an engine failure and leap in your cellphone to complain to the world about your dust bike downside… (sarcasm supposed, nevertheless it’s additionally true in some circumstances).

These are the commonest 2 stroke & 4 stroke dust bike blown head gasket signs:


Whether or not you could have a 2 stroke, 4 stroke, liquid-cooled or air-cooled dust bike, they’ll all overheat. An air-cooled engine will give off noticeably extra warmth, and for those who examine the temperature with a CHT sensor (Amazon) on the spark plug washer, it ought to be close to 350F levels and under 425F.

A liquid-cooled engine temperature might be measured with a coolant temp sensor (Amazon) and ought to be within the 180-220F diploma vary. If it’s over 240F levels, it’s overheating and can begin doing harm.

Overheating will finally trigger the top gasket to fail resulting from excessive temps or the cylinder head might warp and fail.

Coolant popping out of the overflow tube

Once you see coolant leaking out of the overflow hose from the radiator in your liquid-cooled dust bike, that is one signal that your head gasket is likely to be blown. How do you inform if that’s the case, although?

In case you’re idling or using gradual for various minutes, coolant spewing out the overflow is pretty frequent. If it occurs simply as soon as, then the top gasket might be wonderful.

YZ250F Dirt Bike Leaking Coolant Out The Overflow Hose 6 DEADLY Signs of A Dirt Bike Blown Head Gasket & Why
Coolant leaking out of the overflow onto the bottom

Nevertheless, if coolant leaks out the overflow nearly each time you experience and after the identical period of time – that’s a certain signal that you’ve got a blown head gasket.

How do I do know? As a result of it has occurred to me earlier than and may be very irritating to determine after which understand that it’s a must to repair it earlier than it will get worse.

Coolant degree decrease after using

One other frequent symptom of a mud bike blown head gasket is having a low coolant degree after your experience. Identical to coolant leaking out the overflow, if this occurs simply as soon as, then it might not be an actual problem.

However for those who examine your coolant each or earlier than each experience (which you SHOULD be doing to stop issues) and the coolant is under the fins each time, you may need a blown head gasket.

Coolant Leaking Out Overflow Tube 6 DEADLY Signs of A Dirt Bike Blown Head Gasket & Why
Low Coolant

It may very well be a foul water pump seal, but when there’s no water/coolant within the oil (milky oil), then it’s more than likely a blown head gasket.

Working Low On Compression?

The pinnacle gasket retains the cylinder sealed to carry the compression. Compression is when the piston comes up within the cylinder and “squeezes” the air and gasoline mixtures. A leaking gasket won’t be able to comprise all of that compression. 

A compression check will present this, and your dust bike shall be down a bit bit on energy. Most 2 strokes are within the 130-150 PSI vary when compression testing. In the event that they’re under 110, then it’s most likely time for a high finish rebuild.

testing low compression on dirt bike 120 psi
Is your dust bike compression low?

Much less energy

Grime bike engines have to be sizzling sufficient to effectively burn the gasoline combination and take advantage of energy, however as soon as they get too sizzling, they begin to lose energy.

For instance, for those who’re out using all day on the monitor or trails and also you discover it beginning to lose energy, you must cease and shut off the engine ASAP as a result of it might be overheating and the top gasket might have failed.
The longer you experience on an overheated engine, the extra harm you’ll do, which is able to end in an even bigger value when rebuilding the engine resulting from extra components needing to get replaced.

Spark plug fouling

When the top gasket is blow, coolant can leak into the combustion chamber. This coolant can simply trigger the spark plug to moist foul.

How are you aware it’s wet-fouled? Your dust bike stops working and received’t begin and the spark plug tip is moist.

Hesitation/poor throttle response

If coolant is stepping into the combustion chamber, this significantly impacts the air-fuel ratio. In case you really feel your bike hesitating or sputtering with poor throttle response whereas attempting to speed up, there’s an opportunity the top gasket has failed and coolant is leaking into the cylinder.

The commonest indicators of a blown head gasket on a mud bike are:

  • Overheating
  • Coolant popping out the overflow tube
  • Coolant degree decrease after using
  • Low compression
  • Much less energy
  • Plug fouling
  • Poor throttle response

What Causes A Blown Head Gasket?

The commonest causes of a blown head gasket on a mud bike are overheating, a poorly put in gasket, a cracked head, or a gasket failure. 

Overheating too many occasions

Preserving your dust bike on the correct temperature is essential. The extra occasions you boil it over and have coolant spewing out the overflow, the extra probably it’s to trigger larger issues. 

Unhealthy gasket set up

The pinnacle gasket is made to seal out the mating surfaces of the cylinder and cylinder head. In case you don’t correctly set up the brand new gasket, depart a few of the previous gasket materials on a mating floor, or reuse an previous head gasket, the excessive stress of the engine will probably blow the gasket.

Cracked head

A cracked cylinder or cylinder head may cause a lot of issues, together with overheating, coolant leaking, or oil leaking. These can result in a blown head gasket, however in any case, a cracked head is a uncommon however main downside on a mud bike.

If the crack is on the outside of the cylinder head or cylinder, you will notice a hairline rack with a cautious visible inspection. Nevertheless, an inside crack will solely be seen for those who take away the highest finish.

Gasket failure

A head gasket can simply fail all by itself. Even for those who correctly put in it, excessive hours or low-quality materials can fail over time. You received’t know for certain till you’re taking the cylinder head off, sadly.

How To Repair A Blown Head Gasket

A easy substitute of the top gasket can generally repair the issue. Nevertheless, you should get to the basis of the issue if one thing else induced the gasket to blow. 

What precisely induced the top gasket to fail?

Did you merely set up it incorrectly, reuse an previous gasket, or not correctly clear the gasket mating surfaces? In that case, then there’s a good likelihood that simply changing the gasket and cleansing the cylinder and head gasket surfaces will repair your downside. 

Cyl. Head 2 6 DEADLY Signs of A Dirt Bike Blown Head Gasket & Why
You possibly can see the spot the place the gasket failed and leaked coolant @ 12 O’clock

Why Did It Overheat?

Did your bike overheat as a result of the gasket blew? Or did the gasket blow as a result of your bike overheated? There’s a distinction between the 2.

Paying shut consideration to your bike may also help you perceive foreseeable issues.
What do I imply by this?

One thing so simple as checking the radiator coolant degree earlier than every experience will let you already know in case your bike has any ongoing signs, or if a problem occurred throughout your final experience. 

A low coolant degree each time you experience both means you get it too sizzling and it blows coolant out in your rides, or the top gasket has already failed and it’s burning it up as you experience. 

Overheating Leads To Different Issues

Even well-manufactured metals can degrade with an excessive amount of warmth. An overheated engine may cause the cylinder head to warp. 

It received’t be a visible distinction, however for those who examine it with a correct indicator setup, it solely takes a couple of .001 variance to trigger points. A Head that’s warped received’t be capable of correctly seal the combustion of the engine.

There may be now a small hole the place the top gasket is, and that’s the reason it fails. It burns sufficient of the fabric away and loses its seal. 

How To Repair A Warped Cylinder Head

This occurred on my 2001 Honda CR125 cylinder head. I took the top off and was planning on milling off materials to get it utterly flat once more. Nevertheless, I used to be in a position to make use of a flat floor piece of metal and put some 320 grit sandpaper on it. I sprayed some oil on the paper to maintain it from loading up.

I then rubbed the cylinder head on the flat sandpaper. It didn’t take lengthy. I might see the place the low spot was after just some seconds of sanding. I solely went till all the gasket floor was absolutely cleaned up. I’d say it took 1 minute or much less for a whole cleanup. 

Flat sanded a warped cylinder head from Honda CR125
Sanded cylinder head and now it’s prepared to return on.

Wash the cylinder head off with heat water and cleaning soap to stop any of that grit from stepping into and damaging the engine once you put it again collectively.

For suggestions and step-by-step directions on rebuilding a 2 stroke top-end click on right here.