paragliding training center
by Had Robinson & others
Carburetor – Here is
everything pilots will need to know about the Walbro WG-8
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. Too high a value will lean out the engine at high loads and may overheat it!
Carburetor pop-off spring pressure – 1.2-1.3 Bar (17.5-19.0 psi). Rest pressure must be 10 psi or greater.
Carburetor primer lever depth below top of diaphragm cover < 4.0mm
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.
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 run (broken-in).
Engine main bearings – SKF BB1B 447205A
Engine main seals – 18 x 28 x 7 (Use seals made of Viton rubber, not Buna.)
Engine mounts, rubber - UPPER mounts 25mm x 25mm; LOWER mounts 30mm x 30mm; 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.
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
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)
Hub runout – see "Propeller hub face runout" below
Ignition coil primary resistance - 1.1 ±10% 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 coil gap – see "Coil to flywheel gap" above
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.
Pop-off pressure – see "Carburetor pop-off pressure" 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 propeller vibration which can be severe.
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
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 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”) If the gap is too much or too little, the engine will not reach full power.
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.
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 – Only a badly damaged prop causes vibration. 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)
B. Torque Values – If you cannot find the value you need below, use this chart for the proper torque for bolts into steel and aluminum.
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! 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.
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
Carburetor mounting screws - 4 Nm. It is easy to strip the threads in the crankcase. Use of threadlock is not necessary.
Clutch nut 38-40 Nm use of threadlock is not necessary
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.
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. If they are torqued down the same as the nuts beneath, they will damage the air duct.
DO NOT USE A CHEAP 1/4" CLICK-TYPE TORQUE WRENCH. USE A 1/4" BEAM-TYPE TORQUE WRENCH.
Engine mounting button head screws 5 Nm for M6; 10 Nm for M8. Blue threadlock keeps them from loosening.
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.
M4 bolts 2.5-3 Nm
M5 bolts 4-5 Nm
M6 bolts 9-11 NM
M8 bolts 20-24 Nm
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 - 3 Nm Use BLUE threadlock on these screws.
Spark Plug – 20 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.
from Miniplane's maintenance website and other sources
A. OVERALL CONDITION If the ignition and fuel systems are in order, engine performance is directly related to engine compression. If the compression is around 150 psi (at sea level), the engine top end is in good order. If this is the case, replacing parts like the piston or piston ring is unnecessary. Use of the best fuel (AVGAS) and oil (100% synthetic or semi-synthetic with the JASO FD and API TC classifications) 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. It does not mix as well with 100% synthetic oils. If you have to use ethanol fuels, use a semi-synthetic oils.
Plugs should be replaced after 25 hours. Of course, how will you know how many hours the plug has unless you keep a log and have an hour meter/tachometer?
B. MONITOR YOUR ENGINE Maintenance schedules depend on how the engine is used. Thankfully, the engine is just a few inches from the pilot's head so he can monitor it closely. Any growing ping type noise (the rattling of loose bearings) must be carefully noted as destruction of the upper piston rod bearing is a disaster. Top end failure might be an issue after 500 hours or more but few pilots put this amount of hours on their engines over a lifetime.
C. TOP END FAILURE Abused engines and those that experience fuel starvation can experience top end failure very quickly -- in just minutes. Engines run lean for any period of time will burn up the lower piston rod bearing and that means a complete overhaul. With that said, the weakest link in the Top 80 is the ignition which must be checked the moment a pilot senses a degradation in performance. Changing the spark plug is the cheapest and easiest way to improve performance (assuming it is worn out). 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.
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 regularly do a compression test on my engines and record and compare the values to be sure the top end is 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 and carburetor, 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 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 things sooner and more often.
These are the (2) most important maintenance items that must be done after a certain number of hours 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 if you are wondering why the yellow plug is in the redrive.
Every year (minimum) – Rebuild carburetor, including replacing the pop-off spring. Replace fuel filter, change the oil in the redrive,
replace the spark plug, and check the ignition. Replace fuel system hoses if ethanol gasoline is used. If the hoses are stiff, replace
them. 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
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 to look into the cylinder and see what's going on. Those who use AVGAS and
fully-synthetic oil 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.
Always replace the O-ring gasket if the head is removed. Use a razor blade and a Dremel wire brush to clean things up.
Starter – Remove and lubricate center bushing with white lithium grease. DO NOT OVER LUBRICATE!
Redrive oil – drain & replace. Be sure to clean the magnetic tip of the drain plug and check the pressure relief valve.
Every 100 hours
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 (above), replace
everything or pilots can also have their cylinders re-bored at this shop for a modest price and get an oversized piston from
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, if needed. Generally, if there is any knocking in the engine, this bearing must be
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 (suggested by Miniplane) – Pilots can also 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 more economical to just replace everything.
Every 200 hours and more
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.
Frame – check it carefully for cracks. We have a competent shop here who can repair them. Most welding/muffler shops will ruin
Piston – replace if needed. If there is a serious lack of power because of wear, the cylinder will also need to be replaced/refurbished.
Redrives made before 2004 – it might be 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 (the engine will idle and start better).