How To Free A Seized Nitro Engine

Nitro RC Engines can get stuck or completely seize up. It can be difficult to determine if the nitro engine is stuck or seized when trying to spin it over. When it gets stuck, it appears that it is seized up and may not move at all, leaving you to believe it is seized. The truth is that Nitro engines will become stuck if they are Not properly cared for.

Why Nitro Engines Seize Up?Nitro RC Engine

Nitro RC Engines can seize up or become stuck for different reasons. They may hydro lock, pull-start cord jammed, debris, or it has been sitting a long time, these are all reasons nitro Engines can get stuck/set-up.

Hydro lock – If there is too much fuel in the combustion chamber and you keep trying to start the engine, it will flood to the point where it feels seized or jammed. To correct this condition, carefully remove the glow plug and see if the engine will turn over. If it does, then keep turning it over to blow the excess fuel out of the cylinder, then reinstall flow plug and should be ready to start.

Pull-start jammed – the pull cord may have come off the track and jammed. To correct this you need to remove the pull-start assembly carefully. Remove the screws and slightly slide the assembly away from the engine, just enough to get a small precision flathead screwdriver in there. Hold the assembly with one hand and use the screwdriver as a lever and slowly slide it off, pushing it from the center using the screwdriver. This is to keep the spring from popping out of place.

Debris – A stone or other debris may have lodged in the flywheel, making it lock up. Check around the flywheel real good for any debris and remove any that are found. This is common when driving off-road constantly.

The engine has been sitting for a long time – If the nitro engine has been sitting for a long time, the old fuel will become sticky and clog or set up the engine. Sometimes to the point where it will not move at all. To correct this, try pouring a few drops of after run oil in the head onto the piston, though this may not work if it will not move at all.

Free Up A Seized Nitro EngineRC Nitro Engine

If your nitro engine is completely seized and will not turn at all, there is some hope. You have a 50-50 chance that it can be saved. Nitro engines can lock up due to the piston being in the top position when shut off and allowed to cool.

After running a nitro engine, You want to make sure the piston is a bdc position before the motor cools down. The top of the cylinder is tapered and the old fuel left inside can become sticky. This causes the piston to stick to the cylinder sleeve, acting like a seized engine.

Remove the glow plug and see if the piston is up close to the top of the cylinder. Try to turn it over with the glow plug removed. If it still does not move, then remove the pull-start assembly (if equipped) and use a wrench on the crank nut to try to turn the engine over.

DO NOT use too much force or things will break. Using the wrench, if it still won’t turn, then try to use a heat gun and heat up the cylinder (sleeve area) to about 200 degrees and then, with the wrench turn engine over. It should now spin over freely. Once it turns overuse a few drops of after run oil in the glow plug hole and turn it over a few times to let the oil work in and coat the inside of the piston sleeve. You now should be able to put it back together and see if it will run.

After performing the above method, And the engine still does not turn over, you can remove the head and try to use the heat method again on top of the piston and the sides of the cylinder. Remember you want it to reach 200 degrees.

If nothing else works, you can try some good old ATF. Open the carburetor and put some ATF into the crankcase. This will help to loosen the crankshaft in case the crank is locked. Let it sit for 24hrs and then see if it will turn.

When all else fails, you may want to think of getting a new engine.


I hope you found this article to be helpful! As always you can leave a comment below!

9 thoughts on “How To Free A Seized Nitro Engine

  1. Thanks so much for this article! I’d had a brand new, just reached the final stage of breaking in process for my Traxxas 3.3. But I was forced to put all my belongings into a storage unit and it sat for about 5-6 years. It was absolutely stuck, but after following your instructions, I was able to turn the crank by my fingers and watch the piston rise and fall. I may have burned up the electrical start when the engine was still seized, but that’s a cheap fix over a new engine! Thanks a million!


  2. Thanks Tim I have the same exact situation now with my xxx-nt Mach 15, that truck is so seemingly fragile always breaking parts no matter how careful I was, after breaking the pivot block for the 2nd time out of frustration I put the truck on the shelf & didn’t look at it again for probably 15 or 20yrs & I’ve recently been inspired for whatever reason to get it going again, even though I learned that my truck is now considered vintage, I guess it’s taken 20yrs to forgive it for breaking the pivot block & now the motor doesn’t turn I took the glow plug out & put a shot of kroil in it, it’s called the oil that creeps it’s really good stuff & has freed up alot of stuck hardware for me over the years so hopefully it’ll work on that too, I’ll also try turning the crankshaft & the heat gun, didn’t know about that one, i really hope I can get this motor going


    1. David, you are welcome. Glad to hear all is forgiven and wanting to get it going again. This happens a lot to be honest. I am sure you will get it going, Remember patients is key.


  3. Great read, makes me want to get back into RC’s. Haven’t had 1 in well over 20 years. After reading your article I just might get back into them to enjoy them with my Grandsons. Thank You for the useful info.


    1. Hi Robert,
      RCS have really changed over the last few years, However they are great fun for really anyone. If your grandsons haven’t been in to RCs yet, I know they would enjoy it. The Nitro RCS may not be something to start out with, but for ones who are experienced will love them.


  4. Hi, Tim. Nitro RC Engines are not easy to use, and we don’t have much knowledge about it. Not only that, but the complex adjustments in it make people look a little confused, and those who want to fully control it must be patient. This makes me want to study it a bit, thanks for sharing.


    1. Hi Tee Teng,
      Nitro RCS are a lot of fun, however they are not for everyone. As they do require patience and having little mechanical skills will help for sure. Although these models now days have a manual guide to use for your timing and maintenance.


    1. Hi Kavitha,
      You don’t want to replace your engine if it is not necessary. Most of the time the nitro engine can be saved by following these methods.
      Thank you.


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