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Checking the timing on paramotors

This method is the only way to precisely determine the timing of an engine without the need to reference the timing mark on the flywheel.  For example, the Top 80 method for setting the timing is 100% mechanical and must rely on a faint mark on the flywheel (which may be missing) and the coil which may have defects or other anomalies from the manufacturing process.

Checking the timing is not usually required.  If the engine is not performing properly, be sure to first check everything else before wasting time checking the timing.

Special Tools Required

Note: links to sources for these tools may change.

1. Timing wheel – this can be made from a sheet of Plexiglas and this pattern.  Alternately, a camshaft timing wheel may be used.

2. Ignition Timing light and a 12VDC power source (storage battery). This timing light is from Harbor Freight and has a built-in dial to set the advance so the light flashes at TDC.  This extra greatly helps set the timing to whatever value you need.

3. Top Dead Center Dial Indicator 14mm – This can be made from an old spark plug with the insides removed.  Dial indicators are so cheap ($10 on sale in the U.S.) that 5 minute epoxy can be used to set the indicator in the adapter if drilling and tapping a hole for a set screw is impractical.  Cut off all but 3/8" of the threads on the spark plug.  If you do not want to custom make an adapter, get the Laser 2833 Top Dead Centre Indicator which works in conjunction with a dial indicator.  Some method to hold the dial indicator on top of the Laser TDC indicator must be used.  Note: you CANNOT use the cheap TDC indicators because they are not precise enough.  A dial indicator must be used.

4. 24" test lead with clips at both ends

5. Metal pointer that can be clamped to a cooling fin – It can be made out of a thin piece of sheet metal.

6. A method for turning the crankshaft at about 600 RPM.  Any 3/8" electric drill will work along with a drill to socket adapter.

7. Top 80:  Long-reach metric hex bit set – Available from Home Depot.  If the Harbor Freight item (#67890) is used, the access holes in the cooling box will have to be drilled out to 5/16".

8. Top 80: Replacement finger screws.  Pilots who have modest mechanical skills can modify them for reuse.  This is recommended for those who do their own engine work.  It is impossible to correctly torque the finger screws when reinstalling them unless the pawls, washers, and springs are removed.  The cooling fan spins at over 9,000 RPM and must be properly and securely attached.  Some try to re-use these screws and damage their engines as a result.

9. A method to prevent the crankshaft from turning.  Top 80:  A small oil filter wrench or, better, a tie-down strap will work if the clutch nut has not been over-tightened.  If things are frozen, a Vise-Grip chain-wrench must be used to hold the clutch from turning while loosening the nut.  Chain wrenches that have teeth will ruin the clutch.  If possible, apply copious amounts of WD-40 to the area around the nut the night before.  Prior to removing a frozen nut, apply (45) seconds of heat to it from a propane torch.  Minari and others:  Use an open end wrench on the flats of the drive pulley to hold it from moving.

10. 3/8" electric drill.  A right angle drill or attachment makes the job easier.

11. Digital caliper

Steps

The photos below are of the Top 80 and Minari, other paramotors are similar.

1. Remove the engine from the frame and attach it to some immovable working surface.  A steel plate or piece of plywood with holes the same size and spacing as the paramotor mounting bracket should be used.  The plate or plywood, in turn, can be held in a bench vise or attached to some other immovable structure.

2. Remove the starter assembly in order to expose the flywheel and ignition coil.

Top 80: Remove the pawls, springs, and finger screws.  Using the long reach 5mm hex bit, the four cap screws that attach the cooling box to the engine.  Remove the cooling box and cooling fan as one piece from the engine.

All engines: to prevent mistakes, take a Sharpie and draw an arrow on both sides of the cylinder indicating the correct rotation of the crankshaft.  It is easy to get thinks backwards (!) when the engine is in pieces.

All engines: be sure to check the coil gap.  If it is not correct, the timing and engine output will be affected.

3. Remove the spark plug

4. Remove the redrive (Top 80) or whatever exposes the other end of the paramotor crankshaft.

How to Time the Top 80

5. Clutch nut removal  Top 80:  Remove the nut on the clutch.  Install the timing wheel and pointer on the clutch side.  Tighten the nut by hand just enough to hold the timing wheel from turning.

Top 80 engine removing the clutch nut

Minari:  Attach a deep 12mm x 1.25 nut (the nut in the Tusk crankshaft puller/install tool kit works great) to the end of the flywheel end of the crankshaft.  Attach the timing wheel to this end of the crankshaft with a 12mm bolt, a washer, and another 12mm nut. The bolt/nut assembly should be just tight enough to keep the timing wheel from turning easily. 

Minari paramotor with ignition timing wheel attached 

6. Install the TDC dial indicator   Attach the pointer to one of the cooling fins on the engine. Tighten the clutch nut just enough so that the timing wheel will not rotate relative to the crankshaft.  Use the TDC dial indicator to set the piston at TDC (its highest point), adjust the timing wheel to read "0".  A mark may be put on the timing wheel at 15° BTDC (or whatever value used) for reference.  When running the timing light it makes things much easier to see.

How to Time the Top 80

Details of the TDC dial indicator and special holder for attaching it to the cylinder head.  The holder was made from an old spark plug. 

How to Time the Top 80

How to Time the Top 80

7.  Remove the TDC dial indicator after setting the timing wheel to TDC!!!  Double-check that the clutch nut is snug.  If things get loose, the timing measurement will be incorrect.  If the nut is over-tightened, it can crack the timing wheel.  On the Minari and others, tightening the nut too much will bow the timing wheel so that it hits the pointer.

8.  Attach the timing light to a 12V battery.  Open the jaws on the sensor cable of the timing light and wrap the test lead 4X or more around the jaws.  You have to do this because most timing lights will not be sensitive enough to fire with the low energy ignition systems of most paramotors.

9. Connect the spark plug to the secondary wire on the engine.  Connect one end of the test lead to the grounded tip of the spark plug and the other end to the engine (a cooling fin). DO NOT CRANK THE ENGINE UNLESS THE SECONDARY IS CONNECTED TO A GROUNDED SPARK PLUG!  You must have a spark plug connected because the timing light will not work unless there is an actual spark.

How to Time the Top 80

10. Rotate crankshaft   Be certain that you have removed the dial gauge before continuing!  Turn the crankshaft in the correct direction at about 600 RPM from the flywheel side.  As the RPM is increased from 200 RPM, the timing will advance by about 1.5 degrees when 600 RPM is achieved.

Make a note of the timing value.

Top 80 ONLY: The factory method used to initially set the timing gives a mechanical advance of 14.5° BTDC +/- 0.5°.  Pilots who have set the timing to 17° BTDC measured with a timing light have not reported any problems.  Even with the timing set correctly, the actual timing will vary, depending on the rotation speed of the flywheel, the condition of the coil and what the coil gap is.  Measured values between 14° and 17° degrees should not cause any issues.  For every 1° of timing change, the piston moves .004" (0.1mm) and the flywheel .032" (0.8mm).  The timing specification has a tolerance of .002" (0.05mm) which is 1/2° +/- range in the timing or 14°-15° BTDC.

For other engines:  Please check the respective timing specifications.

11.  Recheck timing  Remove the means by which the crankshaft is turned and re-install the TDC dial indicator.  Carefully move the crankshaft to TDC.  The timing wheel must show TDC (0°).  If it does, the timing has been accurately measured.  If not, this means the wheel has moved and the process must be repeated starting at step #6.

12.  Reassemble the engine by following steps #1-5 in reverse.  Always test fly the engine because static tests with paramotors are not accurate because of cavitation of the air around the spinning propeller.  That is, the engine will never be under full load unless it is flying in the air.  You must be flying along at (21) mph to properly load the engine.

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