paragliding training center
by Had Robinson & others
Carburetor – Here is
everything pilots will need to know about the Walbro WG-8
Carburetor idle needle – 1 1/4 turns (1 1/8 turns if above 4,000' MSL) These values are for the initial setting only.
Carburetor main jet – size 116 (sea level). We have the high altitude (HA) jets. Contact us to purchase.
Carburetor metering lever height – 0.5mm - 0.7mm (0.020" - 0.28"). If your ML diaphragm has a tang instead of a button, set the height to 1.70mm.
Carburetor pop-off pressure – 1.2-1.3 Bar (17.5-19.0 psi). Rest pressure must be 0.69 Bar (10 psi) or greater.
Carburetor pop-off spring length, new – 15.0mm Note: old springs can have the same height as new but be defective!
Carburetor primer lever depth below top of diaphragm cover < 4.0mm
Carburetor tubing – 6mm ID x 55cm length and 4mm ID x 20cm length
Clutch bell shaft to redrive housing clearance – 30.5mm. See the clutch page, paragraph B.5 for more details on this clearance.
Clutch bell housing minimum thickness 1.2mm
Clutch springs – overall length 31mm. If more than this, they must be replaced. The clutch should engage at 2,500 - 3,500 RPM
Clutch seals, bearings, etc. – see "Redrive" below
Compression – see "Engine compression" below
Crankshaft – longer end is the flywheel side
Cylinder gasket squish – 0.60mm-0.70mm (0.024"-0.028") For low octane fuel make the thickness 0.80mm-0.95mm. Engines before June 2003
require 0.80mm-0.85mm. New gaskets compress approx. 30%. This must be noted when calculating the gasket size. Most common
sizes are .30mm & .40mm. Excessive gasket thickness is always better than too thin. Too thin a gasket can cause engine damage.
Cylinder head temperature – max 200°C, cruise temp 120°C - 150°C. Temperatures above 160°C should be for brief periods only. Actual temperatures
will depend on load, ambient conditions and altitude. Engines run at seal level will experience greater operating temperatures. These temperatures
have been measured with the TTO CHT. Other brands of CHT's may give different temperatures.
Engine compression – about 150 psi (sea level); 135 psi (4,000' MSL). Values can be 10% less without problems. Do NOT put any oil in the
cylinder before testing. Compression will be less on a engine that has not been broken-in.
Engine cylinder dimensions – This is a table of the piston sizes (letters) for the corresponding cylinder diameter after boring or honing.
Engine main bearings – SKF BB1B 447205A
Engine main seals – 18 x 28 x 7mm double-lipped type FPJ (after Feb, 2014: 18 x 32 x 7mm) These are specialized seals available only from Miniplane.
Engine mounts, rubber – UPPER mounts 25mmL x 25mmW; LOWER mounts 30mmL x 30mmW (or 25mmW); all mounts M6 threads
Engine mounting screws – the screws on the harness side (M6x8) are shorter than on the engine side (M6x10). Use blue threadlock!
Exhaust flange springs/nuts – go here for more information and how to tighten.
Exhaust mounts, rubber (2) – 30mm x 30mm, M8 female x 8.5mm, M8 male x 17mm
Flywheel diameter – 90mm
Fuel – aviation gasoline (AVGAS) or premium grade unleaded gasoline, ethanol free. For more info, see the fuel-oil specification page.
Fuel line size – carburetor to filter ID 1/8" x OD 3/16"; filter to fuel tank ID 3/16" x OD 5/16" – use Excelon fuel line or equivalent. Do NOT use
vinyl tubing. It will become stiff because of fuel additives and stress the connections on the tank and engine. The correct type of fuel line
tubing is available from Miniplane-USA. Auto parts stores do not have the right type of tubing.
Fuel & oil specifications – The correct fuel & oil is critical to engine performance and long life. This is a thorough discussion of the issues.
Fuel pump vacuum – 5" Hg (dry) 7" Hg (wet w/ fuel)
Horsepower – see "Output of Top 80 engine" below
Hub runout – see "Propeller hub face runout" below
Ignition coil primary resistance – 2-3 Ohms
Ignition coil secondary resistance – 8.2K Ohms ±10% (measure with a needle stuck into the secondary wire right where it comes out of the coil.)
Ignition coil resistance + OEM secondary wire resistance – 17.5K Ohms ±10%. With our secondary kit installed, the value will be 8.8K Ohms ±10%
Ignition coil to flywheel gap – 0.38mm (0.015")
Ignition timing – Official value is 14.5° BTDC (0.90mm - 0.95mm/0.0354" - 0.0374") piston BTDC. Check timing Change timing
Muffler springs – Use paraglider line to stretch the springs for replacement/removal. Do NOT use pliers to stretch the springs because
this will nick the tempered surface of the spring and weaken it. Here is a video on how to properly do it
Oil – see our fuel-oil specification page
Output of Top 80 engine – 11 kW (14.8 hp.) at 9500 rpm at sea level
Piston ring, clearance .038mm (.0015")
Piston ring, end gap .178mm (.007") new, max .191mm (.0075")
Pop-off pressure – see "Carburetor pop-off pressure" above
Power – see "Output of Top 80 engine" above
Propeller hub – the propeller hub must be installed and removed with heat! DO NOT USE FORCE! YOU WILL DESTROY THE HUB!
Propeller hub face runout – < 0.013mm (0.0005") Any value greater than this will cause sever propeller vibration.
Redrive bearings – LARGE GEAR, prop side FAG 6003 C3, engine side FAG 6202 C3; SMALL GEAR, prop side FAG 6200 C3, engine side FAG 6002 C3
Redrive bearing seals – prop shaft 17mm X 30mm X 7mm; clutch bell 15mm X 28mm X 6mm (we stock these seals $8 free shipping, contact us to order)
Redrive clutch bell housing minimum thickness – see "Clutch bell housing minimum thickness" above
Redrive clutch springs – see "Clutch springs" above
Redrive fill plug relief pressure – 1.5-2.0 psi (new redrive models only). If this relief valve becomes clogged, the redrive will leak oil.
Redrive hub face runout – see "Propeller hub face runout" above
Redrive lubricant – Miniplane specifies 50 ml of SAE 80W-140 gear oil. 75W-90 100% synthetic gear oil may also be used. Older models of the redrive
(before 2004) use grease. These models do not have a drain plug and must be completely disassembled in order to replace the grease.
Safety net dimensions – these are needed if repairs are made to the safety netting or if pilots want to make their own.
Secondary wire + coil resistance – see "Coil + secondary wire resistance" above
Secondary wire resistance (only) – 8.5K Ohms ±10% As the resistance of the wire is measured closer to the coil, this value will decrease
proportionately. The secondary wire has a resistance of about 570 Ohms/inch (225 Ohms/cm). If the wire from our secondary replacement kit
is used, the resistance is about 13 Ohms/inch (5.1 Ohms/cm).
Spark plug gap 0.5mm-0.6 mm. (.020” - .024”) Always set the gap to the minimum. The greater value is the maximum value, not the range.
You cannot gap the plug correctly without a wire-type gauge.
Spark plug installation and information
Spark plug type – NGK B9ES or B9EG (cold flying conditions) or NGK B10ES or B10EG (hot flying conditions). Do not use resistor type plugs unless you
have replaced the secondary wire with our kit and notice interference in your 2 way radio. The correct heat range for the plug is necessary to
prevent fouling or overheating. Always use RED threadlock on the terminal cap lug. It will loosen, even if it is tightened with a pair of pliers,
if threadlock is not used.
Spring removal and installation – see "Muffler springs" above
Squish – See "Cylinder squish" above
Starter rope – 1.25m x 3.0mm Dyneema. Miniplane-USA has this superior cord over the stock OEM cord. It will last years.
Tachometer/hour meter – see "Cylinder head temperature" above. Not having this gauge is like not having an odometer on a car.
Vibration – A badly damaged prop will cause vibration. However, the usual source is the prop hub which is almost always bent from a prop strike
Weight, dry – 20.5 kg (45 lb) no fuel, includes the complete Miniplane frame
A. Torque conversion chart (Newton meters to/from inch pounds). Here is an online conversion program from Nm to ft-lbs or the reverse.
B. Torque Values – If you cannot find the value you need below, use this chart (in ft-lbs only) from the engineers at Fastenal.com for the proper torque for bolts into both steel and aluminum. This chart from Kohler Engines is in both Nm and in-lbs but is not as complete.
Reduce all torque value by 50-60% with screws made of aluminum or short threads into aluminum, reduce torque by 70% or more with
screws into plastic.
WARNING: button head screws and studs CANNOT be torqued like ordinary screws. Use 30-40% or less torque on
these screws according to the standard table for installing steel screws into aluminum. The correct torque is very important on
bolts/screws that fasten together pieces that have great forces that can separate them e.g. bolts holding on a cylinder
head or the nuts holding on a flywheel. Sufficient torque also prevents fasteners from loosening. Fasteners on aircraft engines cannot
be relied upon not to loosen unless other measures are taken, such as the use of threadlock or wire. There is no fastener on a
paramotor that would be life threatening if it should come loose but it would be inconvenient, at the least, or cause serious damage
to the equipment, at the worst. This is why some nuts are the locking type and why BLUE threadlock should be used in most places.
Use a paint-pen or nail polish to mark important fasteners, like the bolts that hold the engine on the frame. A quick glance will tell you
if they have moved (loosened). If you don't think you need to learn how to use a torque wrench, check this photo of a stripped cylinder
head bolt that pulled right out of the crankcase.
C. Threadlock – read this important page on threadlock and how to use it and when NOT to use it.
D. Engines running near or at sea level run hotter and have greater output which causes things to loosen, especially the cylinder head
If you do not see the particular screw, bolt, or nut below, use the values in this table which are for Class 4.6 and 8.8 fasteners. The lower value is for 4.6 and the higher is for 8.8. The lower values should be used on aluminum fasteners and anything except hardened steel fasteners. Most fasteners on paramotors are made of steel so the higher value may be used.
M4 1, 2.5 Nm
M5 2, 5 Nm
M6 3.5, 9 Nm
M7 6, 15 Nm
M8 8.5, 21 Nm
Carburetor mounting screws – 4 Nm. It is easy to strip the threads in the crankcase! Use of threadlock is not necessary.
Carburetor/airbox mounting nuts - 0.9 Nm (8 in. lb.) Over-tightening these nuts deforms both the air box gasket (which will then jam
the choke in either the open or closed position) and the gasket between the carburetor and the reed valve body.
Clutch nut 38-40 Nm use of threadlock is not necessary
Cooling air duct (cooling shroud) locknuts – DO NOT TORQUE THESE DOWN! They should just be snug (2-3 Nm).
Cooling box to crankcase (4) bolts 10 Nm – threadlock is optional on these bolts
Cooling fan/starter to flywheel screws – see "Finger screws" below.
Cylinder head nuts 9 Nm Tighten in a cross pattern to 4 Nm and then to 9 Nm. Note: do not use thread locking compounds on these nuts.
It is best to use a 1/4" beam-type torque wrench.
Assy order: Short bolt – washer, nut; Long bolt – spacer, washer, nut. After engine assembly, put the large metal washer on the stud,
then the cooling air duct, plastic washer, and locknut. Failure to get the order correctly will damage the cowling. The locknuts
holding the air duct should be just snug (2-3 Nm). If they are torqued down the same as the nuts beneath, they will damage
the air duct.
Engine mounting button head screws – 3 Nm Be sure to use BLUE threadlock on these critical fasteners.
Exhaust button head screws – 5 Nm Install these AFTER the exhaust flange nuts have been tightened
Exhaust flange springs/nuts – see this page for notes and how to tighten.
Exhaust flange studs – 2 Nm. Use RED (high strength) threadlock on these studs or they will loosen.
Finger screws – 10 Nm A 10mm deep socket must be used to tighten these screws. Threadlock is optional.
Flywheel nut 38 - 40 Nm Temporary torque for setting timing 2 Nm. Do not use threadlock on this nut as it is not necessary.
Frame to engine mounting button head screws – see "Engine mounting button head screws" above.
Muffler mounting button head screws – 10 Nm Note: BLUE threadlock must be used on these screws.
Muffler rubber mounts (in engine) – Tighten firmly with adjustable pliers that grip the steel washer on the side that has the stud. Use BLUE
threadlock on the stud – this is very important!
Propeller bolts 6-10 Nm – It is better to be on the loose side when tightening. Note: failure to keep these torqued properly can destroy
the hub. Note: A torque wrench cannot be used on the engine side. Use a hex bit with the torque wrench on the prop side.
Do not over-tighten! Wooden propellers are particularly prone to loosening and must be checked regularly. Replace the locking nuts
when they turn easily or use BLUE threadlock. Make sure the rubber washer is under the outer flange and NOT between the propeller
and the hub/spacer.
Propeller hub center screw 9-10 NM – it is important to use BLUE threadlock on this bolt. Go here for information on removal or installation.
Redrive nuts – 20-24 Nm When assembling be certain to check the clutch for drag before torqueing the nuts down.
Redrive fill & drain plugs – 5-6 Nm. Note: drain/fill plugs are not designed for high torque values. It is easy to strip them.
Never use thread locking compound on drain/fill plugs.
Reed valve screws – 2.5 Nm Use BLUE threadlock on these screws.
Spark Plug – 21 Nm (15 ft. lb.) If you do not have a torque wrench, the plug is new, and you do not have a CHT installed you may use
this method to tighten it. 1. First hand tighten 2. Tighten with a wrench an additional 90-120 degrees. Use of anti-seize compound
on the threads is optional.
Be sure to use RED threadlock on the spark plug terminal (not the part that goes into the cylinder head).
It will loosen, even if it is tightened with a pair of pliers, if threadlock is not used. Some newer plugs have the terminals applied
tightly. I have found out that they, too, will loosen if the terminal is not unscrewed and red threadlock applied.
from Miniplane's maintenance website and other sources
A. OVERALL CONDITION If the ignition and fuel systems are in order, engine performance will be directly related to engine compression. If the compression is around 150 psi (at sea level), the engine top end is in good order. However, my experience has been that the wrist/gudgeon pin and needle bearing must be examined for wear in engines with high hours (> 200 hours). This requires removing the cylinder. A failure of the wrist/gudgeon pin and/or bearing will require a complete top end replacement. Use of the best fuel (AVGAS or premium ethanol free MOGAS) and approved oil) will give your Top 80 the longest life before a major overhaul is necessary. Use of gasoline with ethanol will increase engine maintenance and cause rapid deterioration of fuel system parts. If you have to use ethanol fuels, use an approved semi-synthetic oil.
The spark plug should be replaced after 25 hours and is the cheapest and easiest way to improve performance (assuming it is worn out). Of course, how will you know how many hours the plug has unless you keep a log and have an hour meter/tachometer?
The carburetor must be rebuilt and tested correctly. Stumbling due to fuel starvation will burn up an engine quickly and why the fuel test must be done if problems are suspected. The rest pop-off pressure must be within specifications for good idle and low-end performance. High pop-off pressure will cause the engine to run lean and possibly burn it up.
B. MONITOR YOUR ENGINE Maintenance schedules depend somewhat on how the engine is used. Top end failure occurs without warning which is why the bearing and wrist pin should be replaced at Miniplane's suggested interval (see below). It is difficult for the average mechanic to measure the wear of this part of the engine.
C. TOP END FAILURE Abused engines and those that experience fuel starvation can experience top end failure very quickly – in just minutes. Engines that run lean (hot) may burn up the lower connecting rod bearing and that means a complete overhaul.
D. IGNITION FAILURE The weakest link in the Top 80 is the ignition which must be checked the moment a pilot senses a degradation in performance.
D. REED VALVE It should be tested and, if necessary, replaced if you find performance down a bit after a carb rebuild, a spark plug change, and find the ignition system all in order. That is, the big maintenance items are the usual but if there are still issues, then we look at compression and things like the reed valve. A leak in the reed valve block will cause the fuel pump to fail after the engine warms up. Use BLUE threadlock on these screws. Once you check that the block is correctly torqued down, you will not have to check it again. Technicians at the Miniplane factory sometimes do not properly torque down fasteners on new engines and why pilots must check these things themselves.
E. COMPRESSION TEST I do a compression test on my engines every 50 hours or so and record and compare the values to be sure the cylinder and piston ring are in good shape. If it's 150 psi plus/minus 10% (at sea level) then it's a waste to replace the piston and cylinder. The ignition, carburetor, and the upper connecting rod bearing, in that order, are always the first things which fail on the Top 80. They must be regularly checked. Compression tests of engines with decompression ports can be done but the pressures observed will be substantially less than engines without decompression ports. Engines with flash starters cannot have their compression measured easily except by removing the starter completely and turning the crankshaft with a powerful electric drill.
F. TYPE OF USE This maintenance schedule here is for average use. If you run at full power most of the time, fly near the ocean, or launch from sandy areas, you may have to check and replace things more often.
Changing the spark plug and changing the redrive oil are the (2) most frequent maintenance items on most paramotors. Use a Sharpie to write reminders on the top of the redrive (or other semi-flat area). Any other method will not be as effective. They are easily removed/changed with mineral spirits. This way, you won't forget. You have an hour meter/tachometer installed right? Note: go to this page and look at section D if you are wondering why the yellow plug is in the redrive.
Every year (minimum) – Rebuild carburetor, including replacing the pop-off spring. 1. Replace the fuel filter. 2. Change the oil in the redrive.
3. Replace the spark plug. 4. Check the ignition. 5. Replace fuel system hoses if ethanol gasoline is used. If the hoses are stiff,
replace them. 6. Check the torque of the cylinder head nuts, especially if you run your engine at or near sea level.
After the first 10 hours
Change the oil in the redrive
Give the paramotor a careful lookover for loose fittings, especially the motor mount screws (both sides)
Cylinder head nuts – check torque THESE NUTS LOOSEN AND MUST BE CHECKED REGULARLY If they get loose, all sorts of bad things
Every 25 hours
Spark plug – replace. Plugs can last twice this long but performance will suffer.
Muffler anti-vibration (rubber) mounts – regularly check these to be sure they are not broken or loose. The studs going into
the crankcase can loosen after many hours and chew up the aluminum threads. Use high strength (RED) threadlock on these studs.
Starter pulleys – these pulleys are of poor quality and will self-destruct if not regularly lubricated with spray white lithium grease.
Every 50 hours (Always replace the "O" ring gasket if the head is removed.)
Exhaust flange gasket – Check for cracks and excessive wear. If there are lots of black oil drips in the area, there is also an air leak
and it should be fixed. The flange gasket/cylinder head joint should be sealed with high temp sealant e.g. Ultra Grey, as needed.
This gasket gradually wears out and will crack and leak if left on too long or if the exhaust flange springs are compressed too tightly.
Cylinder head and piston de-carbonizing – Use a scope or a bright light to look into the cylinder via the exhaust port and see what's
going on. Those who use ethanol free fuels will have less maintenance, overall. Be sure that the piston ring is free and the groove
is clean. A stuck ring will greatly affect performance and also tear up the cylinder. Stuck rings are caused by engine overheating
and/or cheap oil. This is the most important routine maintenance required on 2 stroke engines, regardless of the fuel type used.
Starter – Remove and lubricate center bushing with white lithium grease. DO NOT OVER LUBRICATE. Use light machine oil on the spring
instead of grease. All grease does is collect dirt and gums up the spring, making it much harder to wind up. Do people who repair
clocks use grease on the main spring or oil? Think about it.... Do not wait until your starter fails to work – it will be too late.
Redrive oil – drain & replace. Be sure to clean the magnetic tip of the drain plug and check the pressure relief valve.
Every 100 hours (Always replace the "O" ring gasket if the head is removed.)
Cylinder head nuts – check torque value 8 Nm
Clutch links, springs, and the inner hub should be checked for excessive wear. If the links can be wiggled around, the clutch must be
removed and carefully examined. Go to the clutch page for more details. Reassemble with anti-seize compound.
Compression check – this is the #1 way to know what condition the cylinder, piston, and rings are. If it is out of specs, replace
everything or pilots can also have their cylinders re-bored at this shop for a modest price and get an oversized piston from
Miniplane-USA. However, a compression check will not reveal what condition the wrist/gudgeon pin and bearing are in.
Ignition secondary continuity check – you can expect the secondary wire to fail by this time.
Re-drive studs in the engine case – make sure they are not loose. These are SS and will fail after many hours and go into the prop!
Piston roller-cage bearing replacement – It is difficult to measure the wear of this bearing and why it should be replaced every 100
hours. The circlips (springs) MUST be replaced, as well. If the pin (rod) has any wear (grooves), replace it. Note: The
pin (rod) is not available separately. The entire piston assembly must be ordered.
Piston ring replacement, if needed. If compression is down by over 10%, it is better to replace the piston, ring, and cylinder.
Prop bolts – check for tightness. Too tight is as bad as too loose.
Every 150 hours
Hone cylinder – If compression is low, Miniplane suggests that the cylinder be honed. Pilots can have their cylinders re-bored/honed
at this shop for a modest price and get an oversized piston from Miniplane-USA, if needed. It is about the same cost to just replace
everything unless you know how to hone your own cylinders. If the cylinder is honed, an oversized piston must be purchased.
Every 200 hours
Clutch – if the clutch engages at idle or is noisy, the only practical solution is to replace it.
Cooling ductwork on engine – the aluminum fins that are a part of the cooling box will eventually break loose. They are not critical parts.
Cooling fan check – Miniplane recommends replacing it but I am not sure why this needs to be done.
Crankcase oil seals – replace if leaking beyond an acceptable amount.
Cylinder – examine the cylinder wall for the presence of honing (the cross-hatch pattern). If it is barely visible, replace or re-hone the
Frame – check it carefully for cracks. We have a competent shop here who can repair it, contact us for more info. Most
welding/muffler shops will ruin your frame.
Piston, wrist pin (rod), bearing, and circlips (springs) – replace
Redrives made before 2004 – it is a good idea to replace the grease at this time or every five years or so.
See Mark Kubisch's notes.
Reed valve petals – replace them if there is any question of their condition (the engine will idle and start better).