launch at Valle de Bravo, Mexico powered paraglider launching from Evergreen Turf farms

SOUTHWEST AIRSPORTS

paragliding training center

Checking the timing on paramotors

by Had Robinson

UPDATED AUGUST 2018

Checking the timing is not usually required but if you are having engine performance issues, it might be worth doing.  If the engine is not performing properly, be sure to first check everything else, especially the fuel system, before wasting time checking the timing.  If this method is used to check the timing on the Top 80, the starter pawl assembly, the cooling fan, and cooling box do not need to be removed.  If you have the modified finger screws for the Top 80, then removing everything is not much more work.

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 factory 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.  Other paramotors, like the Minari are easier to time.

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 or, better, purchase the Bikemaster or Motion Pro timing wheel from BikeBandit for under $12.

2. Ignition Timing light and a 12VDC power source (storage battery or jump start system). 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 helps set the timing to whatever value you need.

3. Top dead center indicator – This can be made from a cheap dial indicator and an old spark plug with the insides removed.  For details on how to make this tool or buy a commercial one, see the timing page and the "special tools required" section.

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" drill will work, including battery powered.  A drill to socket adapter is needed for paramotors other than the Top 80. (See step #8 below for info on how to turn the crankshaft on a Top 80 without having to completely disassemble the starter/flywheel.)

7. A method to prevent the crankshaft from turning in order to loosen redrive or clutch nuts.  Top 80:  A chain wrench, a small oil filter wrench or 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.

8. Top 80 only: If you do not have the modified finger screws which can easily be removed and reinstalled so that you can remove the starter, cooling box, and cooling fan assembly, you must have some way of turning the starter pawl assembly.

A homemade jug consisting of a triangular piece of thin steel with a 1/4" bolt in the center attached to a modified Top 80 cooling trident plate (#M6S4 4a) works nicely.  Using the jig does not require that the cooling box or any part of the starter assembly needs to be removed.  This jig (in this position – with the trident tangs facing away from the flywheel) will fit nicely inside the starter pawls and contact them so the crankshaft can be rotated.  A socket fitted over the nut and an adapter can be driven by an electric drill.  Optional: Small pieces of windshield wiper hose can be put over the tangs to help protect the pawls.

jig for turning the crankshaft on a Top 80

jig for turning the crankshaft on a Top 80

Alternately, an 1 1/2" cupped wire brush can also be squeezed in between the pawls and then turned with a drill.  Whatever is used does not have to be elaborate or fancy.  Anything that has a shaft that can be turned by a drill will work.  It's worth the time to make the jig as it will save a lot of time and expense.  When we have more time, we'll make one for sale for a few bucks.

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 starter pawls (Top 80) or the flywheel nut (Minari and others).  This must be done in order to have a method to rotate the crankshaft on the flywheel side.

Top 80 only: If the finger screws have been modified, then it is relatively easy to remove the pawls, the cooling fan, and the cooling box.  If you have the OEM (unmodified) finger screws, they must be removed by filing off the top of the riveted end of the screw so that the pawls can be removed and a 10mm long socket used to remove the screws.  Alternatively, you can use the jig above to turn the crankshaft which will save about a half hour.

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 excessive, the timing and ease of starting will be affected.  If it is too little, the center post of the coil may contact the flywheel after the engine gets to running temperature and ruin the coil.

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 using the tools shown.  Alternately, a chain wrench or an ordinary ratcheting strap can be used to hold the clutch.  See step #5 on the timing page for more details.  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.  (You will need to remove the starter.)  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.  Alternately, on non-clutched Minari engines, you can use the factory method.  Note: where the instructions read "magneto", read "magnet".  The factory method is not as accurate but easier to do.  Once you are done using this method, you can skip to step #12 below.

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.

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 the 12V source.  A jump-start battery works very well for this light-duty electrical need.  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 in series because the timing light will not work unless there is an actual spark at the spark plug.  Do not let the steel case of the spark plug touch any part of the engine.  It must be grounded through the test lead.

How to Time the Top 80

10. Rotate the crankshaft   Be certain that you have removed the dial gauge before continuing!  Attach the drill to the jig (Top 80) or the flywheel nut (Minari and others).  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 on most engines  You will know that you are about the right speed when the timing stops advancing..

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.  IT IS ALWAYS SAFER TO BE ON THE LOW SIDE OF THE TIMING ADVANCE THAN ON THE HIGH SIDE.

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 that the timing 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.  This is due to the cavitation of air around the spinning propeller if the engine is stationary.  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 (trim speed) to properly load the engine.

vulture