Engine throwing flames

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Vivek 5T

Vivek 5T

Active Member
Messages
30
Hey guys.. Need help again!!
Finally managed to fix my pull start and got the engine running again.. But!!
Ran the car easy 1/2 throttle half tank since i started the engine after 3-4 years.. Ran fine 1st half tank.. Then.. Started throwing flames, miss firing and shut down.. Refuses to start now!!
 
Interesting. Where were the flames coming from? Perhaps you have a fuel leak or cracked sparkplug (hunch). Leak in a fuel line? Not sure what engine you have, could be a side port plate leak taking fuel mixture into the ducted cooling fan and getting ignited by the engine heat or static discharge on the coil (doubtful). I would assume there are two side ports, I would suspect the one behind the engine blower is the culprit (if the flames were coming out around the cylinder cooling fins.) Take off the body (assuming it was on) and there would be signs where the flames were coming from (assumed). Not sure if a loose header will do this unless you were running too rich, it may just have been a fluke that the spark plug was not fouling or getting wet. Check your spark plug, could have been loose. Does the engine still have compression when you pull on the starter? In other words, I have no clue.
 
Bandit2013 said:
Interesting. Where were the flames coming from? Perhaps you have a fuel leak or cracked sparkplug (hunch). Leak in a fuel line? Not sure what engine you have, could be a side port plate leak taking fuel mixture into the ducted cooling fan and getting ignited by the engine heat or static discharge on the coil (doubtful). I would assume there are two side ports, I would suspect the one behind the engine blower is the culprit (if the flames were coming out around the cylinder cooling fins.) Take off the body (assuming it was on) and there would be signs where the flames were coming from (assumed). Not sure if a loose header will do this unless you were running too rich, it may just have been a fluke that the spark plug was not fouling or getting wet. Check your spark plug, could have been loose. Does the engine still have compression when you pull on the starter? In other words, I have no clue.
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Running the Zenoah g320rc in a losi 5t..
The flames were coming through the exhaust.. Compression seems to be ok..
I suspected i was running a little rich..
 
DougStar said:
Sounds like the timing is out🤔 the key way on the flywheel must be damaged or the key is missing 👍🏻
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How can i check the timing?? What causes the timing to go off?? The flywheel is cranking well.. don’t see any issues there..
 
Doug is on the money here. I thought his response was a good call.

The way I understand it:

The crankshaft had a keyway cut on it that fits a half moon shaped key. The flywheel should have a groove cut inside its bore. This groove and key when mated to the cut on the crankshaft will prevent rotational shift of the flywheel on the crankshaft. It is also indexed on the shaft so that the embedded magnet in the flywheel reaches the ignition coil at the correct time just before top dead center. the collapse of the magnetic field by movement of the flywheel triggers an induced high voltage to create spark at the plug at top dead center or just a fraction of degree past that to keep the piston moving in the right direction during the combustion cycle. If the key is missing or has corroded such that the flywheel can slip on the crank shaft, ignition timing will be lost. If all is good with the flywheel and alignment with the key in the crankshaft, I would suspect the spark plug may have changed in characteristic resulting in delay of the spark and ignition occurs when the fuel mixture gets forced into the combustion chamber. If you changed the spark plug recently, it could be that causing the issue as not all spark plugs are the same, some may have built in resistors. The other thing to look at is the spark gap as that also plays a role when a spark will occur. Larger gap requires more voltage from the coil to arc, this will retard the spark and may occur too late. I doubt that is the actual issue. Ignition coil or type of plug or if plug is damaged internally would be the issue. The other component in the mix would be the ignition wire and spark plug boot. Components will age differently in use or not. A nick on the spark plug wire can also contribute to issues.

Since you recently fixed your pull start, if that involved the use of a piston stopper (assumed if you had to install parts to the flywheel or remove the flywheel nut to install an adapter nut. If the key is compromised by corrosion or if it is not the correct size to start with, applied torque on the flywheel nut may have caused a shift in its position. Long shot but probable.
 
Bandit2013 said:
Doug is on the money here. I thought his response was a good call.

The way I understand it:

The crankshaft had a keyway cut on it that fits a half moon shaped key. The flywheel should have a groove cut inside its bore. This groove and key when mated to the cut on the crankshaft will prevent rotational shift of the flywheel on the crankshaft. It is also indexed on the shaft so that the embedded magnet in the flywheel reaches the ignition coil at the correct time just before top dead center. the collapse of the magnetic field by movement of the flywheel triggers an induced high voltage to create spark at the plug at top dead center or just a fraction of degree past that to keep the piston moving in the right direction during the combustion cycle. If the key is missing or has corroded such that the flywheel can slip on the crank shaft, ignition timing will be lost. If all is good with the flywheel and alignment with the key in the crankshaft, I would suspect the spark plug may have changed in characteristic resulting in delay of the spark and ignition occurs when the fuel mixture gets forced into the combustion chamber. If you changed the spark plug recently, it could be that causing the issue as not all spark plugs are the same, some may have built in resistors. The other thing to look at is the spark gap as that also plays a role when a spark will occur. Larger gap requires more voltage from the coil to arc, this will retard the spark and may occur too late. I doubt that is the actual issue. Ignition coil or type of plug or if plug is damaged internally would be the issue. The other component in the mix would be the ignition wire and spark plug boot. Components will age differently in use or not. A nick on the spark plug wire can also contribute to issues.

Since you recently fixed your pull start, if that involved the use of a piston stopper (assumed if you had to install parts to the flywheel or remove the flywheel nut to install an adapter nut. If the key is compromised by corrosion or if it is not the correct size to start with, applied torque on the flywheel nut may have caused a shift in its position. Long shot but probable.
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I also changed the clutch plater and tightened it with the piston stopper.. I really tightened ts out of the clutch plate bolt as the older clutch plate was slipping..
 
Chaning the clutch would not cause this as Doug said. However, if you did work on the flywheel side of the engine, that could be an issue if something is missing in the assembly or has been compromised. If you have knowledge of the flywheel being removed at any point in time something may be missing. You would need to use a flywheel puller to remove it to inspect the key or groove in the crankshaft. Flywheel is made of cast aluminum, so it lacks any strength to it. Could be a defect in the casting or again, something is missing in the assembly (key). Then again, if the key was made of soft or brittle metal, it could have sheared off. Not sure what it would take to tear a key, I have seen it happen with large 3 phase industrial motors or other equipment used in manufacturing, or even farm equipment. Not something I think about.
 
Bandit2013 said:
Chaning the clutch would not cause this as Doug said. However, if you did work on the flywheel side of the engine, that could be an issue if something is missing in the assembly or has been compromised. If you have knowledge of the flywheel being removed at any point in time something may be missing. You would need to use a flywheel puller to remove it to inspect the key or groove in the crankshaft. Flywheel is made of cast aluminum, so it lacks any strength to it. Could be a defect in the casting or again, something is missing in the assembly (key). Then again, if the key was made of soft or brittle metal, it could have sheared off. Not sure what it would take to tear a key, I have seen it happen with large 3 phase industrial motors or other equipment used in manufacturing, or even farm equipment. Not something I think about.
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I did manage to take the engine apart today and everything on the flywheel side seems to be ok.. Even the key.. The only abnormal part I found was that the piston ring had quite of play in it.. Is there supposed to be?? Its my first time opening up the engine..image.jpg I found was the cylinder head looks a little beat up..image.jpgimage.jpg
 
There should be some play in the piston ring I would assume. That is the way it is with most engines. Should be a snug fit in the groove. Not sure how snug but snug enough to prevent lateral movement of the ring when the piston reciprocates inside the cylinder. Since you tore into the engine, are you planning on rebuild?
 
Bandit2013 said:
There should be some play in the piston ring I would assume. That is the way it is with most engines. Should be a snug fit in the groove. Not sure how snug but snug enough to prevent lateral movement of the ring when the piston reciprocates inside the cylinder. Since you tore into the engine, are you planning on rebuild?
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Will re build the engine in the near future but first get a new engine..
Vivek 5T said:
Will re build the engine in the near future but first get a new engine..
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Do i only need to buy the top end re build kit to re build or do i need other parts too??
 
DDM racing has diagrams of parts for each of the engine sizes they offer parts for. Complete, long block, and kits.
The embossed part number on the crank case housing and the etched number on the piston would help you identify what engine you have as well as what generation or version it may be. They should be able to guide you in what you need to get the job done.

rebuilding engines at this point in time is out of my scope of experience. It looks easy. I only started in the 1/5 scale hobby a few months ago. I will get into engine building if the engine is worth the effort, depends on cost of new complete vs rebuild kit.
 
Bandit2013 said:
DDM racing has diagrams of parts for each of the engine sizes they offer parts for. Complete, long block, and kits.
The embossed part number on the crank case housing and the etched number on the piston would help you identify what engine you have as well as what generation or version it may be. They should be able to guide you in what you need to get the job done.

rebuilding engines at this point in time is out of my scope of experience. It looks easy. I only started in the 1/5 scale hobby a few months ago. I will get into engine building if the engine is worth the effort, depends on cost of new complete vs rebuild kit.
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Yehh.. Buying a new engine is a better option IMHO price wise as well as a sure way of getting the truck ripping again..
Considering that my engine is also now 5 years old.. if I change the internal engine parts and the carb and exhaust.. A new engine is more economical..
So long story short.. I will go for the new engine.. and slowly rebuild the engine and learn stuff about the engine.. Could use the old engine for spares too..
 
It's possible (although highly unlikely) if your piston had that much of a gap, (bad ring(s), per se). That it could have had some unburnt fuel, bypassing the ring, and dumping into crank. At which point, next stroke, it fired out the exhaust, then shut down. (is what it sounds like, to me).
Although, I am with Doug on this as well. Even though the keyway looks good, you did say you tightened the crank, using a piston stopper. (and stated you tightened TS out of it. Granted, the keyway, is enough for it not to retard, or forward (pre-detonate) the timing. To shoot flames (assuming it is ok).

Personally, I would port & polish (in your case, learn as you go) all internals (as needed). spend as little money into rebuild (other than gaskets, etc.)
Try to get it to run right, and go from there.
But in mean time, yeah. Just get a cheapo, prebuilt one.
 
Hey guys.. Finally changed the piston ring and fired the engine right away!! Had success in firing the engine easily.. but its not running as i would like.. the rpm is not stable.. Every time i blip the throttle the engine seems to bog a little and then over compensates.. at idle the rpm keeps fluctuating for about 30 seconds and then the engine stalls.. What could it be?? Please help..
 
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