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JETT ENGINEERING INC. |
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QUICKIE-JETT-I (AMA 426) .40 INSTRUCTIONS click here for Jett II Q40 engine recommendations Thank you for ordering the Quickie-Jett-I Engine from DCRC. We believe that it is the finest, most powerful engine in its class. PROP: A high performance engine should have a well-balanced prop to perform well. Reinforced Nylon, Carbon Fiber or Fiberglass are OK, but use extra care to avoid injury. Pick a prop that turns at least 18000 RPM, but preferably more on the ground to get the best needle valve behavior. We recommend an APC 8.75 x 9W OR 8.8 X 8.5, 8.75, or 9.0. For zero nitro, you need to use a smaller propeller to keep the rpm at 18000+. PLUG: We recommend the Merlin Racing plug, 1125 Red or Green. The Nelson HD works well also, but tends to be a little cold natured in this engine. Use a new plug often for best results. BREAK-IN: We recommend that you do all break in on a test stand, using a remote needle. For the QJ-I, the break-in is easy. Take your 8.8 x 8.75 flying prop and run the engine for 5 minutes at 15000, 5 minutes at 16000, and 5 minutes at 17000. After this initial 15 minutes, you can install your engine and fly. On the first flight, set the engine at about 17000 for launch. This should yield a good rich run. If not, then immediately kill the engine, and check your tank and fuel system for problems. (see below) After the first rich flight, then lean in about 500 each time until you get a good solid run. TANK: A six-oz. Bubbleless JETT tank works well for Quickie, but any good clunk is OK if you have no leaks, keep it clean, and are perfectly isolated from vibration. CLEAN YOUR TANK AND EQUIPMENT OFTEN AND USE A FILTER IN YOUR PUMP. If you mount your engine upright (not recommended) make sure that the needle valve assembly is at least as low as the centerline of the tank (this may be impossible). If not, turn your engine sideways so the engine won't have to draw up hill. If you have engine problems, look at the tank first!!!! This is where we find most problems. ABOUT 80% OF THE TROUBLE CALLS WE GET ARE ULTIMATELY FOUND TO BE TANK PROBLEMS. Also, we have found that some q-500 airplanes have the tank position too low. Hold the fuse and look at the nose from the side. If the bottom front curves upward, and the top is almost straight, then the tank will be lower than if the fuse is designed oppositely. In this case use the Jett CG tank, mounted level and as high as possible. Some examples are the NINJA, VIPER, and the SLINGSHOT. The use of a Jett CG tank mounted at the top of the fuse and on the CG will make your engines run much better through the turns. The engine should run almost a full tank of fuel on the ground without changing RPM significantly. Look for air bubbles in the fuel line while running with 1/3 full tank. You should have no air in the fuel line. A non-bubbless tank must be perfectly isolated by thick, dense foam, around all sides, and front and back. Take the time to do this, along with making sure you have new, good tubing in and outside the tank, and above all else, no leaks. Bubbless tanks solve almost any tank problem you might have and we find them to be good value, even at the extra cost. We use them in all our models, even the standard sport planes. ADJUSTING THE NEEDLE VALVE FOR FLYING: Open your needle one turn from your break-in setting and install your flying prop. Use a small prop that turns at least 19000 at peak. Start the engine and make sure you have a good working Tach. HINT: Put your finger over the pipe for one second to prime the engine. The engine should be too rich to take off the battery, so start to lean it in (clockwise). The engine should start to move up the stages of the pipe and be running above 16000 quickly. Continue to lean it in slowly until the engine starts to smooth out, but still has the "crackle" of a rich setting. If the prop is right it will now be turning at least 17500. As you continue to get leaner the engine will seem to have a second wind above 18000 and climb easily to 19000 and hold. If you have difficulty getting more RPM and the engine sags before you get to 19000, try a different prop, with possibly 1/2 inch lower pitch. After getting the right prop, open the needle valve a turn, start it up and slowly lean in the engine until the peak RPM is found. Do not remain at peak!!! Expect the engine to smooth out, then sag as it gets lean and overheats, quickly open the needle 1/2 turn and let the engine cool. Now you know where the peak is--always stay on the rich side of the peak. A good way to tell if your needle is slightly rich is to pinch the fuel line quickly after you have it set. If it doesn't surge in RPM, it is probably too lean. Hint: These engines are cold natured and may die if you disconnect the battery before the engine is warm. Try pinching the fuel line a few times to warm up the engine before disconnecting the battery. FLYING Start off by finding the peak and then backing down about 1500 RPM to the rich side for the first flight. We recommend that you use a slightly smaller prop for a few flights (19000-19500 RPM). The engine should run rich in the air and land with a wet, shiny-to light amber glow plug, rather than with a dry, powdery, dark finish (lean). During the beginning of the flight, if the setting is too rich the engine may die suddenly in a tight turn, but at the end of the run, if the engine tries to stall in a tight turn, try a richer setting, or more importantly, raise the tank. MAINTENANCE: Your engine is designed to last for many races, but care must be taken to avoid lean runs. A few laps lean will take away hours of life. If you are getting good solid runs and are never blowing a glow plug, then you may be able to run the engine slightly leaner, but watch the condition of the glow plug and listen during flight. It is always advisable to fly with no other engines running so you can hear your engine and its needle setting. Other than avoiding lean runs, the second most important maintenance item is storing the engine dry. Run it dry after flying and store it such that fuel and muffler oil cannot run into the engine. Then use a good after-run oil to protect your bearings. We use Marvel Air Tool oil, found at machine tool stores. Finally check the torque of you head bolts often, especially after you have a hot run. Do not over-torque your head. We prefer light torque, checked regularly. (15-20 in-lbs) Your muffler has stainless steel screws on purpose. They break when you crash and will do less damage to the engine and muffler. Your muffler is assembled with a special high temp adhesive, so if you need to reassemble it for any reason, return it to the factory, or use "red" Loc-Tite from the auto store. (The red will only work for emergency repairs) Proper installation of internal engine parts is important, so we recommend you let us do that. If not, we will be glad to assist you in any way.
TECHNICAL BULLETIN (QUICKIE-JETT-I, AMA 426)
REMOTE NEEDLE VALVE: Your engine comes equipped with a universal remote needle. Installed correctly, you will find it both safer and easier to use. On Q-500 airplanes, it is best mounted directly behind the engine fins, with the needle pointed upward. Other methods may work just as well, but remember the rule that you need a straight line between the tank and center of the carb. You can mount a piece of plywood either inside or outside of the fuse directly under the remote. Use #4 sheet metal screws and a little 5 minute epoxy or Si rubber to mount the remote. Bring out the fuel tubing about 1” (25mm) behind the remote nipple. FUEL SHUT OFF: We recommend that you install a fuel shut off, rather than using the throttle linkage. (AMA rules allow this) If you use the square conforming mount, then drill out the throttle hole to ¼” inch (6.5mm) and deburr the hole carefully. Using 1/32” diameter wire (.8mm), wrap a loop around a 5/32” drill (4mm), two or three turns. Bend the loop such that is centered, and cut off the loop to 1 1/8 turns. This should be a tight fit on the 3/16” diameter Jett “shut off” tubing. Finally, with the backplate installed (no engine) take a ¼” drill and spot into the firewall about 1/8” (3mm) deep. Your loop should completely disappear when pulled back. If not, you can twist the loop smaller or increase the depth of the spot. Before you connect to your servo, test the system to make sure the shut off works. You will find that this system works very well and makes the installation and removal of your engines much faster and easier. Also killing your engine this way avoids flooding and subsequent hard starts during the next racing heat. And no, you cannot do the “Nelson” throttle trick, but it is not and was never necessary on any Jett. To lock the throttle, remove the throttle arm, belt sand, file, or remove about .015 length from the barrel and reinstall. You can also install a Jett Carburetor O-ring over the barrel and tighten. ( I glue it with red Loc-Tite to make sure) PROP SELECTION: Piped engines sensitive to prop selection; therefore the wrong prop can cause many symptoms which lead you to believe you have other problems. For example, two props that vary just 500 on a non-piped engine may vary 1500 on a piped engine. Or, two engines which are just 400 different on a small prop may vary 1000 on a larger prop, yet their air speeds are insignificantly different. In summary, use a small prop (at least 20000) to compare engines, not the biggest one you have. These engines are timed and piped for at least 18000 RPM. If you have taken just any prop out of the bag and bolted it on, you may only see 17000 and think you have a problem. We recommend the APC 8.75/8.8 dia. quickie props. Get several different sizes. Balance the props. It should require very little. Don't use it if it pegs your balancer. Test them all, making sure you don't overheat your engine (see next section). Don't run a prop that does not turn at least 18000 at peak. If you must try a larger prop, get the engine set on a smaller prop, then make the switch without changing the needle. Remember, those big props can fool you into setting the needle too lean. (Read on) ADJUSTING COMPRESSION: From time to time you may feel that it is necessary to raise or lower your head for better performance. There are several rules of thumb which others may give you for this. In general, ignore them and use the time honored system "when in doubt don't". Most often as you travel, or experience different weather conditions you will see a corresponding change in engine performance, but in most cases, this can be fixed by changing the prop. Your engine was shipped to you with the head set for optimum performance in average conditions, but in 80% of the cases a change will not measurably affect your power. In all cases, a change of 2-3 thousandths is all you should consider. If more are required you should look elsewhere for the problem. For a Quickie-I on 15% fuel, the operating range should never exceed .007 to .015. Look to the glow plug to tell you what to do: If you never blow one and the wire shows no sign of heat (a rough, semi-melted look), then you may want to try to remove a .002 shim. Conversely, blowing plugs often may indicate that you need to add a shim. Before you do, though, you must be certain that you are getting good needle settings. A lean run will wipe out a plug regardless of the head clearance. Remember that needle setting has much more to do with blown plugs then head clearance. And remember too, there is no free lunch, the lower the head the higher the maintenance costs. TORQUING YOUR HEAD: If you have a torque wrench, be careful how you use it. It has been shown that many of these tools are not as consistent as you are with your fingers. Use a screwdriver handle type hexdriver, not a T-Handle wrench. Make sure all of you bolts are clean, and will screw completely down without sticking. If not, run them in a few times until they loosen up. Clean all the critical parts with a paper towel: The cylinder flange. The head surfaces. The gaskets. The head clamp where it touches the head button. The screw holes and head bolt seats. Next, seat the gaskets and head button on the cylinder and place the head clamp on top. Grasp the head clamp with two fingers and hold it down tightly while you spin the bolts down with the hex between your fingers--don't touch the handle yet--just your fingers on the small hex. When the bolts touch (you are still holding the head down with your fingers) go to the next one across, using a 1-4-2-5-3-6 crisscross until you have them all touching. Work the circle twice. Turn loose of the head clamp and tighten once again with your thumb and index finger on the handle. Always work the circle twice. Finally torque the head bolts to the desired amount with your torque wrench or by hand. About 16- 20 inch-pounds. It is more important to do step one--seat the bolts--than any other. If you skip it you will find that you torque wrench will give you as much as 100% variation in torque, which can surely ruin your engine. MEASURING HEAD CLEARANCE: If your engine is not overly tight, put the piston at top dead center before removing the head. Measure the height from the top of the sleeve to the piston with a good depth mic, not calipers, then take note of the sleeve: Does it lift up off the case as you rock the shaft back and forth? If so, you can measure the amount it rocks with your depth mics(usually about .001-.003) and subtract it from your reading. You can also measure bottom dead center and subtract the stroke. This method is foolproof, but you do need to know the stroke within 1/2 thousandths. The Jett .40 is .708. When measuring the head it is usually safer to measure the bare head and gaskets separately. REV. 1-10-10
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