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How to Fix a Seized 2-Stroke Engine? (Best Method)


Fix a seized up two-stroke engine.

A seized 2-stroke engine puts an immediate damper on your afternoon dirt bike ride, snow blowing, or whatever activity you had planned. But all is not lost, and it is possible to fix a seized 2-stroke engine and rescue your weekend plans!

Fixing a seized 2-stroke engine is usually best achieved by applying force to turn the piston over and break down whatever has caused it to seize. Depending on if the engine is cased in aluminum or cast iron, it may or may not be able to handle the force to fix it.

The cast iron can usually handle the process to fix it, but weaker aluminum may not be able to make it through the fixing process depending on the seizure, in which case the best bet will be replacing it entirely. We’re going to look at a step by step process to fix a seized 2-stroke engine.

What is the Best Method for Fixing a Seized 2-Stroke Engine?

There are several steps involved in getting your engine back to working order. If you’re more of a visual learner, follow along with this youtube video for some visual indicators of the steps below:

How to fix a Seized Gas Powered String Trimmer
  • Remove the spark plug: The location of the spark plug will vary based on what device you are working on, but locate and remove the small spark plug so that you have access to the combustion chamber.
  • Lubricate the chamber: A lot of people like to add industrial lubricant, like WD-40 or Marvel Mystery Oil (link to Amazon), to the combustion chamber and then replace the spark plug. Let this sit for a few hours at least before moving on to your next steps.
  • Turn the crankshaft: Use a clamp or pliers to firmly grasp and turn the crankshaft, manually turning over the piston. You may have to remove a pull cord cover, depending on what the engine is attached to. 
  • This is the point where, depending on your housing, the force of manually turning the crankshaft could break some surrounding housing materials. The crank should turn easily once freed.
  • Fill it up: Be sure to fill up the engine with a high-quality two-stroke oil (link to Amazon). Having the wrong amount of fluid or running on gas alone is a common cause of engine seizure in the first place, so be sure to invest in quality fluids. 
  • Crank it up: Try to start the engine using either the pull cord or whatever starter your particular device or vehicle uses. If all the above steps went smoothly, then it may take a few tries, but the engine should start right up. Let it run for a few minutes before pushing it too hard to let the oil run through and keep things smooth.

What Made the Engine Seize in the First Place?

There are a couple of different things that may have seized up the engine. Ultimately, the blame usually falls on the user and is usually a result of some sort of mismanagement. The most common cause is running the engine without oil. Because the metal of the piston gets too hot and expands faster than the wall of the cylinder, the piston seizes itself.

The engine can still run without oil for a bit before completely smoking out. But without the oil, all the machinery is banging right up against the other parts resulting in tons of premature wear and tear. This sort of beating is what most people will find to be their problem.

Running without oil isn’t the only way a small 2-stroke can seize up. Things can get more complicated with something like a dirt bike, instead of a lawn mower, despite both using 2-stroke engines. 

Dirt bikes are under significantly higher amounts of stress than any outdoor lawn care appliance or tool. Without proper care, these are even more likely to struggle than other small engines. You’ll want to be sure to check your gaskets and cylinders regularly to keep things running smoothly. 

For instance, a broken gasket could lead to an air leak. Super lean conditions can be caused by stray air leaking into a cylinder and will often lead to an engine seizure. It’s also possible that the tolerances are too tight, which ends up not leaving enough clearance for the piston to expand and shrink normally.

What About a Cold Seizure? 

This one is tricky because the name is confusing, but really this is a result of heat. Cold seizures happen when the machine is started and pushed too hard too fast. The engine needs some time to warm up, otherwise the cylinder can’t keep up with the rapidly expanding piston. When you start up the engine, let it run for a minute before pushing it to full throttle.

What to Do if the Method Above Didn’t Fix It?

If you’re feeling bold, you may want to take apart the whole engine to better diagnose the problem. This YouTube video should prove helpful to follow along in that if you’ve never done it before.

TAKING APART THE TWO STROKE ENGINE!

When you take apart the engine, you should be able to discover if there is something else that has caused the seizure and is possibly in need of replacement. Ensure that the piston hasn’t cracked from pressure and isn’t dinged up all over the top from stray debris that found its way into the chamber. 

Some light scuff marks on the piston are nothing to be too worried about, but any sort of big dents or cracks are definitely cause for concern. If you’re seeing any parts that are looking severely damaged, you’ll want to head to the local mechanic and find some replacements. 

You can try and use some heavy-duty sandpaper to scrape off any aluminum deposits that may have accumulated on the wall. These deposits could be obstructing the needed clearance for the piston to fire.

Is It Worth It to Repair a Seized Engine?

This one is going to really be up to you to consider. It’s definitely worth trying to repair the engine using the method above. But once you start taking the engine apart, you’ll want to pay close attention to the cost of parts and time spent. 

Ultimately, only you can decide how much your time is worth. The fix might come pretty easily, but it might also take a good amount of time, effort, and money on parts. 

There are definitely certain instances where it is likely to be cheaper and easier to find yourself a new machine. It all comes down to what parts need replacing, if any, and how much your personal time is worth. 

Can You Fix a Seized 2-Stroke Engine?

The answer is sometimes, but you can always try! You may be among the lucky ones who have simply had a short spell of bad luck and with a little lube and muscle, can work through the problem. Though you may also find yourself in the less lucky pile of people who need to dismantle and replace some engine parts. 

Before going to all that effort, though, give the method above a try for starters. Cross your fingers and hopefully you’ll be mowing the grass or cruising the trails in no time!

Teddy Henderson

Teddy is always fiddling with small engines, picking up thrown-out string trimmers or tearing apart dirt bikes. He shares what he learns along the way. Hopefully, you'll have less headaches than he has had by learning from his mistakes.

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