KX100 engine for aircraft

Danappger · May 6, 2005

Turns out it's the connecting rod bearing on the crankshaft which is frozen; as the questions I now have are more general I posted a new thread asking about what to do.

-Dana

bikepilot · May 7, 2005

I'v seen that happen on KX100's as well, but dont be discouraged, they don't seize often. My sister's kx went over 300 hours before the bottom end went (and it gave plenty of warning prior to going).

good luck - I'll go look for your other thread:)

Danappger · May 30, 2005

Well, everything's back together and I flew the new machine for about a half hour today until the winds picked up. This time all went well; the biggest problem was a spotty idle, which should just be a matter of some tweaking. No bearing problems this time; I suspect the bearing got dirt in it either when it was on a bike, or when it was in storage... when I got it it was covered with dust and no carburetor on it; though I cleaned it out when I had it apart there still may have been something in the bearing.

Strangely, it wouldn't run right with any filter, even a simple screen, directly over the carburetor. Of course in the air I don't need anything like the filter you'd need on a dirt bike... some don't have filters at all. Adding a 12" length of car radiator hose to the carb, with the screen over that, worked fine and even seemed to gain me a couple hundred rpm... perhaps it smooths out the airflow. A bit quieter too... though it's still a noisy beast.

I also bypassed the powervalve this time... I left the flapper and wedge in place, but I machined a block to fill the compartment on the cylinder and block it wide open, and I also removed the centrifugal governor and linkage from the crankcase. As far as I can tell there's no difference at all at high or low rpm's, throttle response is fine... low end torque isn't an issue with a propeller. One less moving part to worry about!

I'll probably pitch the prop a tiny bit higher... in flight rpm's were around 11,300 at full throttle, not too bad but I wouldn't mind getting it down around 11,000. Power is very noticeably better than my old 15hp machine, so I'm a happy camper. :)

-Dana

bikepilot · May 31, 2005

Sounds good. I am not sure why it wouldn't run with a filter, my guess would be that the intake track between the carb and filter must be a certain distance/volume. A stock KX100 has a rather larger oiled foam filter. Be carefull without a filter, these engines are very sensitive to dirty air (might be a problem on take off??) as the air/fuel charge circulates through the crank cases. Do take the time to get it jetted properly, the engine will run better and last longer. For extended high rpm uses you probably need a little colder plug than stock, a B10EIX would be my top pick (the "10" is the heat range(higher number = colder), the E is the length(19mm/3/4"), the IX is the electrode type (iridium).

Lastly, keep an eye on the reeds, they typically start to fray at the tips and may do so more quickly with your useage. If/when you replace them, look for high tension reeds (typically designated as race or rpm reeds and made of carbon fiber) as these will be more resistant to flutter at high rpm.

good luck and enjoy - I'm envious of your flying machine, though I do get a 1/2 hour of aerobatic "training" in a T-6 in june:)

Danappger · May 31, 2005

That's what I think, it's probably a volume thing. I'll try the K&N filter again when I get the chance; as it is the screen (pretty fine, actually a piece of nylon stocking from the wife) will keep out anything you'll find in the sky, I'm not down in the dust like a bike. Except for the idle I think the jetting is OK as the plug looks pretty good; the plug is the one that was in the engine when I got it, a B8ES, though I'll probably try a BR9ES. I don't want to foul a too-cold plug, either, during an extended idling descent.

Have fun in the T-6, I'd love to do that. I did do acro training in a Stearman years ago, though, that was a blast!

-Dana

Campaigns to bearproof all garbage containers in some national parka have been difficult, because as one biologist put it, "There is a considerable overlap between the intelligence levels of the smartest bears and the dumbest tourists."

bikepilot · Jun 1, 2005

Changing the plug would be a good idea. The standard plug for that bike is a 9, the 8 is only really for slow trail riding where the standard plug would not get up to temp. Many use a 10 for MX racing to prevent detonation from an overly hot plug. The 8 should run to hot with much wide open throttle/high rpm and may throw off your plug readings. The 9 should not foul. My wife's KX100 has a 9 in it and she rides it very slowly at low rpm and lets it idle quite a lot and has not managed to foul a plug yet. I would recomend using a BR9EIX, its the same tempature range as a BR9ES, but has a .7mm irridium tip that is much more resistant to fouling than the large tip on the ES plugs. It will give you an extra measure of safty should you have a long decent and an overly rich idle mixture without running too hot at full power. The "R" in BR9EIX is just for Resistor, you don't really need a resistor plug unless you are using some sort of electronic equipment. I typically use them because my bike requires them and its nice to be able to use the same plugs in all our bikes.

With the powervalve open all the time, you will probably need to lean the idle mixture a bit. If it seems to be runnign rich at idle as I expect it is, I would recomend going one size smaller on the pilot jet and tweeking the air screw to get it fine tuned (in = less air = richer, out = more air = leaner). Neither will have any affect at high throttle settings.

Just out of curosity, what exhaust system are you running?

btw I love quotes in your sig - a pic of the paramotor would be cool to:)

Danappger · Jun 1, 2005

Thanks, I'll probably try the IX plug if it's available. I want to use a resistor plug so it doesn't interfere with a 2-way radio if I'm using one (we sometimes use FRS radios to talk to each other in flight).

Why would leaving the powervalve open make it necessary to lean the idle? Opening the powervalve effectively tunes the pipe for a higher rpm, and vice versa, but I don't see how it would affect the idle mixture, since it's not "on the pipe" at that point. I actually thought the idle was too lean, and forgetting that the adjustment is an air bleed and not a fuel control, I leaned it further... which didn't help. Being eager to fly, though, I kept it running by blipping the throttle until I was ready to launch, at which point idling was no longer required. :)

To be honest, I don't know for sure what the exhaust is. It's not from a KX100, I know that, but I think it may be from a YZ80, cut and rewelded to fit it into the space available. Certainly it's not optimized, but it seems to work pretty well... and if I'm not developing the engine's full potential power that's probably good for longevity. Eventually, though, I want to try to buy an exhaust made for the engine, but unwelded, so I can put it together in the shape I need without having to cut out the existing welds as I did with this one.

You can see pictures on home.comcast.net/~d-m-hague/parafan.

-Dana

A seminar on Time Travel will be held two weeks ago.

bikepilot · Jun 2, 2005

I was just guessing that with the pv open, the cylinder will not be scavenged as efficiently. But your experence certainly makes it look like an lean mixture. The air screw will probably not make a big enough difference to get it to run well. I know my wife's KX100 will idle with it all the way in or out, it makes a differnece, but not much. Pilot jets are cheep and easy to change though. It may be usefull to turn up the idle speed screw as well (it just holds the slide open - clockwise = higher idle).

I would recommend getting the exhaust set up properly when you can, the YZ 80 motor is very similar and its probably not far off though. The IX plugs are easy to get a hold of. Most mc shops stock them, but bob's cycle (http://www.bobscycle.com/links.html) definitely has some. I bought two BR8EIX's from them a couple of weeks ago. Limiting the power with inefficient exhaust will not necessarily increase TBO. For example, a dented pipe that restricts the exhaust flow can cause egt's to rise enough to melt a piston. The expansion chamber is effectively an exhaust valve, it is tuned so that the fuel/air charge actually flows through the cylinder and out the exhaust port, then the returning sound/pressure wave pushes it back into the cylinder just before the piston closes off the exhaust port. Again, this is just theory, I have no idea what the differences between a YZ pipe and a KX pipe are. Dynoport might be a good source of exhaust parts, they make pipes for bikes from several cone sections and have been known to make custom pipes as well. It may be worth having them design and manufacture custom pipes for your application when you are ready to sell the kits (you may have one potential customer here:)).

good luck and please keep us posted:)

Danappger · May 25, 2006

Update

Just an update, I have about 13 hours flight time on it now. I'm guessing about 25hp since climb performance is identical to a friend who has a 25hp machine, same weight, same wing, etc. Jetting got me good reliable operation and I did go with the IX plug. I've been playing with prop pitch and find that if I go too high I can't get the rpm's, it never gets up on the pipe... but if I prop it so it maxes out around 10,500 to 11K it's good... and climbs like an express elevator!

Biggest headache is the pipe now. The mounting compromises I had to make by using the original bike pipe means it cracks every few flights... and I'm getting tired of welding it. :pissed: Anybody got a suggestion for a custom pipe builder? I contacted Procircuit, FMF, and Bills about buying an unassembled pipe so I could weld it together in the orientation I want but none of them will sell one that way. Worst comes to worst, I suppose, I'll have to fabricate one myself, but I'd really rather not.

-Dana

Beware of strange faces and dark dingy places,
Be careful while bending the law.....

ttr125biker · Dec 21, 2006

well i don't know aviation but i have a suzuki rm100 dirt bike (extremely similar engine as the kx100 because suzuki and kowasaki are the same company) and i think you should expect huge maintnance. many of the the dirt bike riders do new piston rings everY 20 hours and at the constant high rpm you intend to use you can expect even more maintnance but if you put the radiator near the prop i think the cooling should be great
how big are the fuel tanks on powered paragliders usualy?

Danappger · Dec 21, 2006

It's not that bad... first the normal rpm's aren't that high, level flight is around 7800 or so, and a steady rpm (even if high) is easier on an engine than constant ups and downs. Also unlike a bike it can never overspeed, and it's operating in a clean environment, with excellent cooling, and never being bounced around like a dirt bike is. Similar spec engines in ppg's can easily go 200+ hours between overhauls. The radiator isn't too close to the prop but remember it's always clean (no dirt or mud) and always in a 20 mph airflow.

A PPG gas tank us usually around 2 gallons.

I finally gave up on the bike pipe. I'm now running a karting pipe from FMF, originally designed for CR80... I lengthened the inlet about 1½" to bring the powerband down, and pitched the prop for 11,000 rpm at WOT, which gives me very good performance and better throttle response than the bike pipe. More importantly, I was able to mount it much better eliminating most of the vibration stress, though I haven't gotten enough run time on it to really prove it out... I haven't flown it for awhile, it was damaged when the wind dragged it while unattended and other projects have prevented me from getting around to the repairs, and with another paramotor and an airplane to fly it just doesn't seem that urgent.

-Dana

California Raisins murdered - cereal killer suspected!

griffbones · Dec 21, 2006

Just out of curiosity did you have to go with a richer or leaner pilot jet to fix your idle problem? BTW I have been loving this thread! :cool:

Danappger · Dec 22, 2006

I never messed with the pilot jet... the only problem with the idle, i think, is not the mixture but that it's too slow; idling with the drag of the prop (since there's no clutch) is just a little too much for the engine... plus when I'm standing up and hooking in, etc., the engine is tilted way over (like tilting a bike way over on its left side). The ultimate solution will probably be to drill out the carburetor body and put in a larger diameter idle speed screw.

-Dana

When Columbus came to America, there were no taxes, no debts, and no pollution. The women did all the work while the men hunted or fished all day. Ever since then, a bunch of idiotic do-gooders have been trying to "improve" the place.

2strokerfun · Dec 22, 2006

Aren't you losing a whole lot of prop efficiency by trying to turn a 47.5" or 49" at those speeds?? I've flown my whole life and you start losing prop efficiency at about .85 mach tip speed. I built a Kolb Flyer ultralight about 15 years ago with two Solo 210cc engines--same or similar engines to what you once had. Built fairly heavy prop adapters to act as flywheel and ran ungeared 36" props at about 6,000-7,000 rpm. Worked very well, but even at those speeds, I was losing some efficiency. Even though the Solo engines were rated at 22 hp, I also only got about 14 hp out of each of them at the speeds I was running. (Darned solid little engines--only problem I ever had in 200 hours of flying was not paying attention to my fuel level--flying is a whole lot easier on an engine than dirt bike use). Prop pitch and density of the wood made a HUGE difference in climb ability. Best of luck and watch out for powerlines!!

Danappger · Dec 22, 2006

Yikes! No, I'm using the engine's original 3.4:1 primary reduction... the prop shaft is driven by the original clutch gear, so the max prop speed is under 3300 rpm.

Kolb Flyer, huh? I just bought a Kolb Ultrastar last week. Haven't flown it yet, gotta do some minor work on it first. My other paramotor has a Solo engine, that one has a 2.5:1 reduction. The stock Solo (with the "lunchbox" exhaust, which is what I have) is indeed only 14hp; a tuned exhaust can bring it up to around 20. Direct drive you lose a LOT of efficiency; even a 49" prop with redrive is only around 33% efficient at paramotor speeds (a bit better in a faster plane).

-Dana

You do not need a parachute to skydive. You only need a parachute to skydive twice.

KX100 engine for aircraft

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