Profi Engines Worldwide

Tech Info

Watch for tech notes to be added periodically. Some prop changes have been incorporated.

Some information regarding the Q500 engine. Please feel free to forward any questions or information you have and we will try to post answers here.

1. Screws for the engine are 3mm and require a 2.5mm hex key to loosen or tighten. The muffler uses 5-40 x 1.5" screws and require a 3/32" hex key.

2. Base head space with no spacers installed is .004" to .006"

3. First flights during the break-in process should use the low pitch 8.75x7.0NN at approximately 21K. Subsequent, race performance will be achieved with higher pitch props. Use 8.75x8.75NN - 8.8x9 to become familiar with race performance. Props that allow ground RPM of 19,800 to 20,300 give excellent airborne performance. This will allow proper exhaust tuning after release at takeoff.

4. The Profi Needle valve assembly uses a nylon insert/seal in the collet. When installing the NV in the spray bar the first time run the collet up the needle far enough that it does not contact the spray bar. When the needle is bottomed tighten the collet to get the needle tightness you prefer. If you try to screw the needle through the collet it will act like a jam nut and prevent the needle from screwing in all the way.

5. The needle valve can be set closely by following this method during break-in runs

Start the engine and let it warm up then set the needle at a rich setting

Hold the nose of the model up at 30-45 degree until the engine stages and runs clean

Bring the nose to level, the engine should stay staged for 5-10 seconds before falling back rich

Change the needle such that it will run clean for a few seconds

Point the nose down, it should fall off the stage

Fly the model, watch the exhaust trail.

Exhaust smoke indicates to much head space, to little pitch or rich needle, make change, fly again

You can achieve a similar setup by pinching the fuel line to get the initial needle setting

5. FAI no nitro fuel will require minimum .03-.05mm (.001"-.002")head spacer after break-in. Start with 8.75x7.00 propeller then establish correct fuel settings and allow high in air rpm. Increase the pitch until the engine will not stage on the pipe in flight. Do not be concerned about ground rpm settings. Low quality castor oil used in some FAI fuel will create varnish on the piston and sleeve. It can be removed by rubbing with a pink rubber eraser (pink rubber has no abrasive). Good FAI fuel results have been achieved with APC 8.75x8.75NN

6. This engine is very "easy" on glow plugs. Use the "hottest" plug you have available to achieve clean runs with the richest needle setting. This is where the most power is developed while using the highest pitch prop.

7. After break-in runs you can remove head spacers.

8. Profi piston material will last for a very long time. The piston has 4 tapers and the seal band will form about 2.5mm from the top. Keep all dirt away from the engine when starting or running. Clean the engine thoroughly after each run, especially if the landing was in dusty conditions. It is advisable to wash all running residue from the engine with kerosene after flying sessions (or even after each flight) then use a quality after run oil.

9. When removing the cylinder head be sure to remove the glow plug then run the piston to the top of the stroke before loosening the screws. This will prevent the sleeve from rotating when you replace the head.

10. It seems break-in takes a long time unless the engine is run for a number of flights with a prop allowing 21,000 or more rpm on the ground. The suggested APC 8.75x7.0NN will be a good place to start break-in flights.

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This site was last updated by Judith 12/23/07