Specifications for the Polini Thor models

Torque values    Maintenance intervals

Most troubleshooting, assembly, & tips are the same as with the Top 80.


Carburetor – The Thor 100 and 130 use the WG.  The Thor 190 and 200 use the WB. The Thor 250 uses the Polini carburetor.

Carburetor jet sizes – Thor 100 #116 (?), Thor 130 #130

Compression, engine – 130-150 psi, depending on altitude.  This is what you can expect for a new engine.  Used will be less.

Cylinder base gasket – thickness 0.5mm, install gasket with the lettering facing down.  Never use sealant on engine gaskets.  It is unnecessary (manifold gaskets are the only exception)

Cylinder decompression port cleaning – use a #39 or 2.5mm bit.  There are (2) holes that go from the cylinder to the exhaust port.  The head gasket must be removed.

Cylinder head gasket – install with the ridge on the gasket UP

Cylinder Head Temperatures – running & maximum (for brief periods <1 minute):

Thor 80 running 55C° max 95C° (water cooled)
Thor 100 running 230C°-250C° max 265C°-280C°
Thor 130 running 230C°-250C° max 265C°-280C°
Thor 130 EVO
running 230C°-250C° max  265C°-280C°
Thor 190 Light running 200C°-230°C max 250C°-260°C
Thor 190 EVO running 200C°-230°C max 250C°-260°C
Thor 200
running 230C°-250C° max 265C°-280C°
Thor 200 EVO running 230C°-250C° max 265C°-280C°
Thor 250 

Flash starter

Fuel filter Info – Use a 10 micron inline filter.

Fuel line/tubing size – Use Tygon® LP1100 Low Permeation Fuel Tubing (ethanol resistant).  It is available from Miniplane-USA.  Do NOT use ordinary vinyl tubing as it will become stiff quickly and stress the connections on the tank and engine.  Auto parts stores do NOT have the right type.

Fuel pump vacuum – 5" Hg (dry) 7" Hg (wet w/ fuel)

Fuel Info – Note: The Polini manual specifies that pilots use unleaded fuel (the only kind available to pilots in the EU).  We contacted Polini and they specifically stated in writing (available on request) that pilots may use AVGAS in any of their engines.  However, we no longer recommend AVGAS because of the problems of deposits fouling the cylinder head and piston, including ring sticking.

Ignition, coil – The official Polini user manual states that the spark plug boot terminal to ground is 5K Ohms.  Some Thor models may have greater values.

Ignition coil primary resistance (all models except the 190) – 1K Ohms (blue wire to engine ground).   If you get no value switch the Ohmmeter leads.  If the value is greater than 1K Ohms, the coil may be OK but, if it is not giving a spark or a weak spark, consider replacing the coil.

Ignition coil secondary resistance – 9K Ohms ±10% (spark plug terminal to engine ground)  Can be 5K Ohms on newer models.

Ignition magneto coil resistance – 290 Ohms

Ignition magneto voltage output – see the Ignition troubleshooting page on how to measure this AC voltage

Magneto – see "Ignition magneto voltage output" above

Mounts, engine – 30mmL x 30mmW x 8mm (stud x socket) There are (4) mounts, total

Muffler spring removal – 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

Power output

Propeller shaft, seal – 26 x 36 x 7 mm

Redrive oil – Here is a list of the correct oils that may be used in the Thor redrive.

Reed valve – if the petals get weak, chip, or break into pieces the engine will not achieve full power or may not run or start.

Spark plug (other than the Thor 250) – NGK BR10EG, gap 0.9mm (0.035")  Pilots may also use non-resistor plugs e.g. B10EG/ES or B9EG/ES.  The "EG" series plugs are designed specifically for 2-stroke engines and also reduce fouling but cost more.  Use of a non-resistor plug will only increase the amount of noise created by the ignition that may be picked up by a two-way radio.  Note: for screw on terminals only, be sure to put the terminal on with RED THREADLOCK or it will loosen and self destruct.  The inside of the spark plug boot may also be damaged. 

Spark plug for the Thor 250 – see the Thor 250 page

Special tools for the Thor engines.  These include the special pullers used to disassemble the engine.

Starter cord – 1.8m (6') When cord is fully installed, wind the spool 3X to ensure adequate tension on the cord which keeps the pulley out of the propeller.

Starter cord pulleys – Harken 082 (superior to the OEM Viadana)

Starter mounting screws – (3) 5mm x 80mm and (1) mm x 25mm.  However, the bottom 80mm screw should be replaced with a 90mm screw and locknut.

Torque values Thor engines

WARNING!    WARNING!    WARNING!  The bracket which connects the engine to the two lower mounts on the frame WILL eventually loosen.

If you don't think you need to learn how to use a torque wrench, check this photo of a cylinder head stud that was pulled right out of the aluminum crankcase by applying too much torque to the cylinder head nut.  The threaded hole in the crankcase was ruined.  It was an expensive mistake for the owner of this engine.  For help, take a look at this video on torque.

over-tightening a cylinder head nut

Torque values and discussion – start here if you are not experienced in torqueing fasteners or need torque values not found in this section.

Polini torque values for various parts

Carburetor screws 6mm – 8 Nm

Compression relief valve – 10 Nm

Crankcase screws 6mm – 8 Nm

Crankshaft nut, clutch side – 60 Nm

Crankshaft nut, starter side – 40 Nm

Cylinder head nuts – be sure to re-torque head nuts after the engine has run a few hours

Engine to frame button-head screws 8 Nm – 10 Nm – use Blue threadlock

Exhaust stud nuts 6mm – 10 Nm – use RED threadlock.

Magneto bolts – 9 Nm

Muffler button-head screws 8mm – 10 Nm – use BLUE threadlock

Propeller central screw – 40 Nm

Reed valve screws – 8 Nm


Starter mounting screws – 2-3 Nm  It is easy to over-torque these screws.  Threadlock is not necessary on these screws.

Maintenance intervals

General instructions

Changing the redrive oil and the spark plug are the (2) most important maintenance items that must be done.  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.  The markings are easily removed with brake cleaner or mineral spirits.  This way, you won't forget!  You have an hour meter/tachometer installed right?

writing reminders on the Top 80 redrive

A. REDRIVE SERVICING  It is very important to change the redrive oil on schedule because it gets quickly contaminated with clutch material.  If your clutch oil appears really black when you change it, increase the change frequency.  Note that the redrive will use oil because of slight leaks out of the relief valve and why it should be changed often.

B. Below are service items that are particular for the Polini.  Pilots would do well to carefully study the servicing intervals for the Top 80 which I have developed to ensure long engine life for any 2 stroke aviation engine.  The carburetor and fuel system are the most common items that must have regular service.  Failure to regularly service the carburetor can result in permanent engine damage.

C. The Polini Thor Flash starter is a disaster.  See the Flash starter page for more information.  Later models may have fewer problems, hopefully.

First 10 hours

Every year (minimum)

Every 25 hours

Every 50 hours

Every 100 hours – this is an important and extensive service of the engine.  Everything may be fine for 150 hours but then maybe not....

Every 200 hours

Every 400 hours