How Do I Know If My Dirt Bike Engine Is Seized?

Did your dirt bike just lock up? How can you tell if the engine is seized? There could be a lot of damage done, but you can usually find the problem in a short amount of time. 

Having your dirt bike seize is not only frustrating, it’s downright dangerous if it happens at just the right time. This article will help you figure out what is seized, why it happened, how to fix it, and how to help prevent it from happening again. 

Piston that overheated and seized in the cylinder.

What Happens When A Dirt Bike Seizes?

An engine seizure is a straightforward, yet major issue. The most common signs of a seized engine while riding a dirt bike are the engine coming to a stop, the rear wheel locking up, and the kick starter being stuck. 

An engine seizure may happen over a matter of several seconds and you hear the engine start to die. This is similar to running out of gas. The engine can also seize almost instantaneously. If internal parts come loose, it doesn’t take long for everything to come to a complete stop. 

That’s when things get interesting. Hopefully it would only happen when riding on flat ground. 

What To Do When A Dirt Bike Seizes

Generally, the best thing to do when a dirt bike seizes is to grab the clutch and pull it in. Hopefully that will keep the rear wheel spinning. If the clutch locks up then you will just have to hold on tight and try to muscle the bike to keep it going straight.

The rear wheel will be locked up and skidding. You can try using the front brake to help slow the bike down quicker. Unfortunately, it will all happen so fast that your natural muscle memory and instinct will likely kick in. This is why it’s so important to wear proper riding gear in case an accident happens. 

What Causes A Dirt Bike To Seize?

There’s many reasons why your bike could’ve locked up. The most common causes of a dirt bike seizure are:

  • Overheated engine/piston
  • Low engine oil
  • Cold Seizure
  • Chain derailed/broke
  • 4 stroke valve contact
  • Engine sucked up water
  • No oil in fuel (2 stroke)

Overheated Engine

A dirt bike engine that gets too hot will eventually seize. Metals can only take so much heat before they start to melt. An overheated piston or ring will burn away and weld to the cylinder wall.

It will probably start scratching away the cylinder wall first, and then quickly transition to seizing and locking up. 

Did You Run It Out Of Oil?

Low oil or overused oil is a very common issue in dirt bikes. The oil is what keeps the engine parts from wearing on each other. If there’s not enough oil between them, friction will start heating them up. 

More friction and heat will cause them to “score” or wear one or both parts away until they stop working or seize together. If your dirt bike starts making loud ticking or knocking noises, you might be due for an engine rebuild.

Cold Start Seizure

A cold seizure is when an engine is first started (cold start) and then it heats up too quickly, causing internal parts to over-expand and seize together. 

Metal parts expand as they increase in temperature. A smaller metal part can be warmed up quicker than a larger part. If the smaller part grows too quickly then it will expand into the larger part (piston into the cylinder). 

This is why you need to properly warm up your dirt bike before riding it hard. The most common cause of a cold seizure is not allowing enough time for the engine to warm up. Pistons and crank bearings can and will seize sooner than later. 

Maybe The Chain Derailed

A chain that comes off of the sprocket(s) can do some major damage. If it pops off of the rear then the front countershaft sprocket is still driving/spinning the chain. It will quickly bunch up at the front sprocket and lock up.

This commonly results in a cracked engine case because of the sudden force of the chain hitting it. A strong sprocket guard will greatly reduce the chance of it happening, but it’s not a guarantee.

Keep Your Chain Properly Tightened

A loose chain can easily cause it to derail, which is why it’s so crucial that you keep the chain properly adjusted.

Hitting a hard object, such as a rock or log at the right angle can also derail the chain. A chain guide protector is supposed to prevent this from easily happening. If your bike doesn’t already have one then you should consider adding a chain guide.

Did A Valve Hit The Piston?

4 stroke dirt bikes have so many more engine parts than a 2 stroke. While most dirt bikes are fairly reliable by today’s standards, a liquid-cooled 4 stroke motocross bike is still a high-performance machine.

It requires more strict maintenance intervals, and the internal engine parts have tighter tolerances to produce amazing power.

What’s The Result?

A valve that lets go or hits the piston will cause a major catastrophe. The piston, valves, head, and probably cylinder are the most likely to be scrap parts afterwards. The crankshaft connecting rod may be bent as well.

The most common causes for a valve hitting the piston is a worn timing chain, or improper clearances.

Incorrect camshaft timing or not enough piston valve relief if you’re running a different/high compression piston, high performance camshaft, or a larger valve. 

Hydrolocked From Sucking Water

Have you ever water-logged a dirt bike? Swamping a bike is easy to do if you ride in a lot of mud holes.

If the water is deep enough to cover the airbox while riding or after a tip-over, there’s a good chance that the engine will suck in water and cause it to seize. 

How To Fix A Hydrolocked Dirt Bike

A hydrolocked engine can be fixed without replacing anything if damage hasn’t been done, but careful attention must be made. 

The main thing you have to do is get the water/foreign substance out of the engine, exhaust, and intake. This may require tipping the bike upside down (turn the gas off first), removing the spark plug, and inspecting the airbox and carb. 

Water will have probably reached the oil, so that will need to be flushed out as soon as possible. 

Burning The Right Oil Mixture?

Are you riding a 2 stroke? Unless it’s oil-injected, you need to run a pre-mix fuel that has the correct gas/oil mixture. The oil is what lubricates the top-end. 

If there’s not enough oil, the extra friction will induce more heat and wear on parts such as the piston and rings. Too much heat and it will seize the top-end. 

To learn what oil mixture you should be using in your 2 stroke dirt bike and why read this article.

Can You Fix A Seized Engine?

A seized engine can always be fixed. The amount of work required depends on what parts have seized and how. A complete new top-end may be required including: piston assembly, cylinder, head, and maybe even a crank if it’s bent. 

A piston that is stuck may be able to get unstuck by dis-assembling it, but there’s more than likely damage done. A piston, cylinder, or rings that are scored (scratched) that can be felt with your fingers needs to be replaced or it will cause excessive wear and result in more damage if you continue to run it.

How Do You Fix A Seized Engine?

First, you need to figure out what needs to be replaced. A 4 stroke needs to have the complete valvetrain (head, valves, cams), piston, cylinder and crankshaft inspected. If the damage was limited to the top-end, then you can most likely just replace the broken/worn parts. Make sure you install a new cam chain and consider upgrading your chain tensioner.

A 2 stroke has less parts, so it will generally be cheaper to rebuild. The top-end is fairly simple to rebuild (read here on How-To)

How To Prevent Your Dirt Bike From Seizing

There’s many ways to prevent your dirt bike from seizing. Most of them are easy to do if you just pay attention. 

How often do you change your dirt bike’s oil? Changing the oil and oil filter are the most important maintenance routines. Keeping the air filter clean is right up there as well. 

Dirt bikes can get really hot. I mean temperature-wise hot. Any bike can overheat if there’s no airflow to cool it down. Keeping an eye on the coolant temp will give you an idea if your bike is about to boil over and steam out the overflow tube

Jetting also affects temperature more than you think. Fuel helps cool the piston during combustion. If the jetting is too lean, then there won’t be enough fuel to properly burn and keep the temps down.

Bottom Line:

Keeping your dirt bike well maintained, running cool, tuned correctly, and always warming it up properly are the most important ways to prevent your dirt bike from seizing!

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