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What will happen if you don't have air gap between coil and flywheel on a small engine

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The "Air Gap" is adjusted to create an electromagnetic "charge" between the magnets of the flywheel and the coil of the ignition system. Without the correct clearance it will not produce the spark necessary to fire the spark plug. When the magnets pass closely to the coil, to make it simpler, it produces this "charge" which is then amplified by the coil that can produce as much as 25-50,000 volts
I don't want to make this sound like rocket science, but the fact is if the coil touches the magnets it will wear out the coil and the magnets and not create the right spark. Too much clearance and it will not produce a spark. I first started working with small engines in the early-to-mid 60s and discovered that by taking a sheet of note-book paper and folding it into about three layers thick, placing it between the magnet and coil loosening the coil so that the magnet would pull the coil to make contact and tightening the coil in place. The clearance would then be satisfactory to make a good spark.
It would then be a simple matter to turn the flywheel to rotate the paper out from between the flywheel and coil.

Posted on Oct 19, 2013


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NO FEELER GAGE REQUIRED! Read through these steps first and get the concept in your mind before you proceed.

  • Remove coil wire from sparkplug if attached. ( always the first rule!) Verify there are no metal shavings or rust stuck to the flywheel magnet. ANY SUCH will prevent operation!
  • Loosen the screws of the coil so that it is snug but moveable and place the coil and flywheel magnet in direct alignment,
  • Secure a sheet of notebook writing paper.
  • Cut the paper so you have 3 layers of paper the width of the edge of the flywheel.
  • Move the loosened coil away from the flywheel and place the 3 layers of paper in the gap with no metal touching.
  • Allow the coil to fit up to the magnetic field.
  • Gently pull the flywheel toward the coil to allow for any clearance or wear in the flywheel bearing.
  • Verify the coil is still snug to the paper and tighten screws of the coil.
  • Turn flywheel with your hand and verify there is a gap.
  • Apply small sideways pressure again toward the coil as you turn the flywheel. Again, there must be NO contact.
Once you have success with the above, you may test the output of the coil by placing the removed sparkplug on the plug wire. With the threaded end touching or clipped to the engine metal, whirl the flywheel quickly with the magnet passing the coil. You should see or hear a spark at the thread end of the plug. Easy!

Oct 27, 2016 | Troy-Bilt Garden

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Air gap for coil

Assume you are asking for the air gap between the flywheel and the ignition coil?

Obtaining the correct gap from the manufacturer's specifications is best because although in theory a close gap is desirable for efficiency, flywheels grow as the engine heats up and a large flywheel can grow quite a lot.

Brass feeler gauges are best for setting air gaps as they are none-magnetic. A typical air gap would be in the region of 10 to 14 thou.

Mar 16, 2016 | Garden

1 Answer

Breaker points gap on kawasaki fa210d small engine

For the FA210D engine, points gap is 0.3mm to 0.5mm on max open. Coil to flywheel gap is 0.5mm. Timing has to be set when edge of left coil core lines up with flywheel trailing notch before the magnet.

Jun 16, 2012 | kawasaki W 2 (SS Motorcycles

1 Answer

Engine does not start. Starter & solenoid work fine. Checked air filter, fuel filter, fuel level, level in choke position. Plug is kind of flooded. Increased plug gap slightly. There is no spark....

Most small engines use a flywheel with a magnet embedded in it and an ignition coil with a core that sits a few thousandths away from the flywheel. Ignition coils are common failures probably because they come from our wonderful Chinese friends. They have demolished all US manufacturers. If you replace the coil, use some gauge to measure the gap between coil core and the flywheel magnet surface before removing the old coil. Otherwise you may spend a little time using trial & error to get the engine running again.
If your engine is a Briggs and Stratton, you can find very complete maintenance downloadable information on their website. This will pertain to the engine only, not the mower.
Dunno about Tecumseh, haven't had much need for service info on those.

Jun 30, 2011 | Cub Cadet Lawn Mower Electric PTO Clutch...

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My 5 hp briggs stopped running. No spark. took recoil off to reveal a rotten coil with wires rotted off. cleaned off the flywheel and replaced the coil with one from Napa. The engine does not have points...

Did you set the Air Gap correctly, it should be .020 inch. If the Air Gap is correct and you cleaned the pickup magnets, you should be getting spark. I have different color coded plastic sheets of the correct thickness to set the Air Gap on different engines. You could use a use a side panel from a plastic soda bottle (Mt Dew, Pepsi, ect) Place it between the Flywheel and the Armature/Ign Coil. Allow the magnets on the Flywheel to pull the Armature/Ign Coil together and then tighten the Armature/Ign Coil bolts. Carefully turn the Engine while pulling the plastic from between the Armature/Ign Coil Pickups. The Armature/Ign Coil is now properly set.

Generall speaking for a gasoline engine to run you need 3 things. (1) Spark, (2) Gas and (3) Air.

I hope this is helpful. UAW 974

Jun 25, 2011 | Sport & Outdoor - Others

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The Torx head screws holding the coil in place have to be loosened. They may be tough as sometimes when assembled, the factory uses Threadlocker on them (alongwith the cylinder bolts). If you have removed covers and are at the flywheel/coil area rotate the flywheel till the magnets in it line up with the leg or legs on the coil. Insert a business card (folded in two) in between and let the magnets "draw" the coil onto the card. The proper gap is about .010-.014" or so. The closer the better. Make sure to tighten the coil screws extra tight. You can coat them with some thread lock if you choose so they can't vibrate loose. The business card gap works on most small engines.

Aug 14, 2010 | Troy Bilt Tb70ss Gas Trimmer

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Have 10 hp Tecumsa engine and can not get ignition spark from plug. Have new spark plug, cleaned flywheel & coil with emery cloth. Have checked on/off switch for continuity. Can ignition coil be tested...

Did you check, that the magnet is on the flywheel.
When you cleaned the flywheel, did some metal rasping gather around it.
The magnet should be strong. A small steel instrument will be pulled by it.

The high voltage coil can be tested for resistance with an Ohm meter. The resistance may be some kOhm but not MOhm. If MOhm it should be replaced.

If the coil and magnet are OK, and well attached to the flywheel and aside with a minimal air gap, then the coil may be checked by turning the flywheel. As the voltage on coil ends when magnet passes by the coil should be very high, the only way for checking is with a spark plug, connected to the checked high voltage cable, the thread of the plug well connected to motor case. A spark is the prove that it is OK

Check also the HV cabel and the connection of other coil end to motor case.

I hope that this will be helpful, because I don't have your device in front of me. Some people rank such an answer with 2 thumbs (meaning useless). Better don’t rank.

Jul 28, 2010 | Coleman Powermate Premium Plus 6250W...

1 Answer

Air gap at the flywheel and coil on a 4 horse

Gap is .008 to .012. But use a brass feeler gauge.

Apr 22, 2010 | Craftsman 25cc Gas Line Trimmer

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What is left to do but change the flywheel?

check what they call air gap between the coil and flywheel .010-.012 gap
also be sure your flywheel is in time.
you will actually have to remove it to do this and check for the sheared key or be sure the key way aligns with the crankshaft keyway on the flywheel

May 17, 2009 | Mantis 2-Cycle Tiller

1 Answer

No fire

Two possibilities left.
You have a short in your stop circuit or bent/out of place component. To check this unhook the small wire on the coil and tuck it out of the way. Put your recoil back on and try to start it. If it starts you need to follow the wire and look for any exposed wire. No exposed wire then you need to follow the mechanical portion of the on/off switch, something is not aligned right or a spring is worn out.

Next check your flywheel to coil air gap. Place a cover of a notebook or a piece of cardboard from a cigarette pack between the flywheel and the coil. This will get you the proper air gap. Then tighten down the coil. If that's not it, you have a bad flywheel. It's very rare but does happen.

Note: while you have the flywheel exposed, clean it up with light grit sandpaper (180 grit or finer) or steel wool. Rust can interfere with the electrical field.

Mar 31, 2009 | Husqvarna , No.455 Rancher, 20" Gas -...

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