paragliding training center
by Had Robinson
Timing 2-cycle paramotors is not an easy task, even with the correct tools. Some, like the Top 80 and Minari, do not have a movable coil assembly. For this reason, the flywheel has to be clocked relative to the crankshaft. The Italian paramotors commonly use IDM ignition systems which also includes the flywheel. These flywheels are slightly different for each paramotor but the location of the magnets are identical. The most accurate way to check the timing is to use a camshaft timing wheel and a timing light available from any auto parts store.
If the timing is too far advanced, the engine will knock, which can destroy it. If the timing is too far retarded, the engine will lack power and overheat. Timing must be set properly for the engine to run its best. Clutched and non-clutched engines often have different values due to the lack of inertia in clutched engines that is required to "kick" the piston past TDC (top dead center). Those who have clutched engines with a non-flash starter know how difficult they can be to start.
1. Top dead center (TDC) dial indicator 14mm – This can be made from an old spark plug with the insides removed. Dial indicators are so cheap (in the U.S.) that (5) minute epoxy can be used to set the indicator in the modified spark plug if drilling and tapping a hole for a set screw cannot be done. Alternatively, an Innovative Products of America 7880 14mm Thread Top Dead Center Indicator along with a clamping dial indicator gauge can be used but this will cost much more than making the indicator yourself.
Here are the details of the dial indicator and the homemade holder for attaching it to the cylinder head. The holder was made from a used spark plug. Be sure to shorten the threads on the used spark plug to a 1/2" or so (not shown below). It will decrease the number of turns you have to screw the tool into the cylinder head.
2. Top 80 only: Long-reach metric hex bit set – Tekton makes a set for around $22 U.S. If the cheaper Harbor Freight item (#67890) is used, the access holes in the cooling box will have to be drilled out to 8mm (5/16") in order to fit the shank of the tool.
3. Top 80 only: Replacement finger screws. Pilots who have modest mechanical skills can also modify them for reuse. This is recommended for pilots who do their own engine work. It is impossible to correctly torque the finger screws when reinstalling them unless the pawls and springs are removed. The cooling fan spins at over 9,000 RPM and must be properly attached.
4. Wheel puller – It is necessary in order to safely loosen the flywheel from the crankshaft.
5. Some method to hold the flywheel and the crankshaft. A socket on the opposite crankshaft nut can be used to tighten things but to loosen the flywheel nut, some other method must be used, such as a small oil filter wrench, a tie down strap, a Vise-Grip chain wrench, or a homemade tool, such as this one for the Top 80.
The drive pulley on the Minari (non-clutched version) has a pair of flats which a 30mm open end wretch will fit. However, the redrive mounting plate must be removed in order to fit the wrench on the pulley.
6. Bench vise and a custom drilled steel plate to firmly hold the engine while working on it. Clamping one of the motor mounts in a vise is not a safe way to secure the engine. An alternative would be to use some screws to mount the motor to a board. The board could be mounted to a table with clamps. Whatever way is used, the motor must not be able to move while you are working on it.
The Top 80 and the Minari have identical ignition systems. However, they have different steps in setting the timing. The Minari technique is easier to do than the Miniplane. If you want to save some time and trouble, follow the Minari sections starting in step #8 below. Always check the timing after you have completed the steps below to be sure it is set correctly.
1. Remove the engine from the frame and attach it to some immovable working surface.
2. Remove the pull starter assembly.
Top 80: Remove the starter pawls and finger screws which will allow you to remove the cooling fan. (See the removal section of finger screw and starter pawl removal and assembly on how to remove these parts.) The cooling box and cooling fan are removed as a unit. The cooling fan cannot be removed with out drilling out all of the rivets on the cooling box and separating the cover and the box. For reinstallation, see this page (see step #9) for help in how to hold the pawls in the correct position when reattaching the starter to the cooling box.
Top 80: Cooling box removal Using a long reach 5mm hex bit, remove the (4) cap screws that attach the cooling box to the engine. Use a 4mm (5/32") bit to drill out the rivet head that holds the primary wire to the cooling box. Do it just enough so that the head of the rivet is removed. Do NOT continue to drill the actual rivet that is in the cooling box. Once the head of the rivet is removed, the clip and wire will pop off. Use a 3mm (1/8") punch to punch out the rest of the rivet. Removing the cooling box exposes the flywheel and the ignition coil. Reinstallation: When reinstalling the rivet, orient the clamp so that it faces the rear of the engine.
Minari and others: Remove any plates that cover the flywheel. The flywheel and ignition coil must be fully exposed.
All engines: to prevent mistakes, take a felt tipped pen and draw an arrow on both sides of the cylinder indicating the correct rotation of the crankshaft. It is easy to get this confused (!) when the engine is in pieces.
3. Remove the redrive (if there is one) or whatever exposes the other end of the paramotor crankshaft.
4. Remove the spark plug
5. Loosen the flywheel Top 80: Hold the clutch with a small oil filter wrench or a tie-down strap. If things are frozen, spray some WD-40 on the shaft nut. Wait a few minutes and then use a Vise-Grip chain wrench, strap, or oil filter wrench to hold the clutch from turning while loosening the nut. Chain wrenches that have teeth will ruin the clutch. Preferably, use a strap to hold the clutch. This is the safest way to keep things from turning. Remove the flywheel nut.
A small oil filter wrench, a nylon strap wound round the clutch many times in the right direction, or a chain wrench will safely hold the Top 80 clutch.
Alternatively, take a tie-down strap and wrap it around the Top 80 clutch four or five times. Double it back around one of the redrive studs and stuff it under itself. This is the safest and most secure way to hold and clutch from moving if there is no oil filter wrench available.
Minari and others: Hold the drive pulley with the correct sized open end-wretch. Remove the flywheel nut.
All engines: Use a wheel puller to loosen (but not remove) the flywheel from the crankshaft. Hold the puller so that the flywheel and puller do not fall off the crankshaft. Reinstall the flywheel nut and tighten just enough so that the flywheel can barely be turned by hand relative to the crankshaft.
6. Secure the engine Top 80: Carefully put the clutch of the engine in a vice as shown in the photo below. Small pieces of wood may be used to protect the clutch.
Minari and others: Leave the engine as per step# 1 above. Paramotors other than the Top 80 do not need to be secured by the clutch.
7. Set TDC Top 80: Set TDC with the TDC dial indicator. Set the outer dial to "0" at TDC. Now turn the engine clockwise so that the piston moves down 0.90mm-0.95mm (0.0354"-0.0374") per the dial indicator. Jam the engine crankshaft at this position with a wooden wedge that can go between the clutch and the crankcase. The crankshaft must not be able to move relative to the crankcase. The higher the dial indicator value, the greater the advance of the timing. If the cylinder was marked with an arrow indicating the flywheel rotation, the crankshaft will be rotating in the reverse direction.
Minari and others: Set TDC with the TDC dial indicator. The crankshaft must be held in this position while the flywheel is moved to the correct position. Turn the flywheel in the direction of the engine rotation and measure TDC just before the dial indicator moves down. It is better to have the timing slightly retarded than slightly advanced on older engines.
8. Set the timing Top 80: Rotate the flywheel so that the mark (about 10mm from the edge of the leading magnet) is even with the lower coil flange (see photos below). A felt tipped pen can be used to highlight the timing mark. The timing can be initially set and then double-checked with this simple and accurate method that uses a timing light and a camshaft timing wheel.
The nut must be tight enough to hold the flywheel so that it will not be affected by the strong pull of the magnets to the coil. Once the flywheel is adjusted correctly, remove the dial indicator.
Minari (clutched & non-clutched): Make sure the piston is at top dead center and stays there (see step 7b. above). The flywheel nut must be tight enough to hold the flywheel so that it will not turn relative to the crankshaft due to the the strong pull of the magnets on the flywheel to the coil.
For the clutched engine, set the timing by aligning the edge of leading magnet on the flywheel with the trailing edge of the coil, as in this photo from Minari. This will give a value of 15-16º BTDC. Note the dimple "A" in the flywheel and its location.
To double-check the setting for the clutched engine, observe the distance between the left edge of the dimple on the flywheel and the leading edge of the coil which should be 44.00mm ± 0.2mm.
For the non-clutched engines, Minari has this PDF with photos for setting the timing. Lining up the rear of the leading flywheel magnet with the leading (inner) edge of the coil advances the timing slightly and gives a value of 18-19º BTDC.
All engines: Once the flywheel is in the correct position, remove the dial indicator.
9. Tighten the flywheel nut 38-40 Nm. Be very careful not to change the position of the flywheel relative to the crankshaft.
Top 80: With the oil wrench filter wrench or the strap method, hold the crankshaft while applying torque. Miniplane makes a special tool for this but it is not easily available. Be careful while applying torque to the flywheel nut. Any relative movement of the crankshaft and the flywheel will change the timing.
Minari and others: Use a wrench on the drive pulley or a socket on the drive pulley nut to hold things as you tighten the flywheel nut. Be careful while applying torque to the flywheel nut.
All engines: Any relative movement between the crankshaft and the flywheel will change the timing.
10. Coil Gap Be sure to check the coil gap. If it is not correct, the timing and coil output will be affected, especially at idle.
11. Check the timing using this method to be sure it was set correctly. The flywheel nut must be torqued to specifications or the flywheel may move relative to the crankshaft when the timing is checked with this method.
12. Reassemble the engine by reversing steps #1 - #4. Test flying the engine will ensure that everything has been done correctly. Be sure to carefully observe the peak running temperature. Engine overheating can be caused by excessive retardation of the ignition timing.