Weedwhacker Engine Project

[sanddrag]

I've had this little 18cc weedwhacker engine for a while now (runs beautifully by the way) and I can't figure out how to start it. I have already machined a mount and shaft for it. See, the pull starter is on the front of the engine, not the back, so I had to remove the pull starter to mount the engine because the only bolt locations are on the front (actually, they are the ones the pull starter housing mounts to.) So anyhow, now I've got this nice little engine on a nice little mount with a standard 3/4" keyed shaft and no way to start it. No, I did not think this project through, LOL Anyhow, I was thinking to use a 3/4" clutch bearing on the end of the output shaft, and then make an adapter shaft that fits this bearing into a standard 1/2" chuck drill. Will that work to start the engine? McMaster says the bearing can take 16 ft-lbs of torque, is that enough?

I know a chainsaw engine would be much better but its the fact that I've already got this one and I don't have a chainsaw one that makes me want to pursue success with this one.

[greencactus3]

you didnt mention what it was for? or did i skip some lines? must be the advil.. lol

[NoodleKnight]

So if I'm right, you're going to start the motor by back driving the output shaft with a hand drill? If so, it should work, it's just like push starting a go-ped (except a smaller engine). Now, for that clutch bearing, it depends on the effort needed to crank the engine (18cc doesn't sound like it'll be too heavy).

I'm also curious; what are you planning to do with the weedwhacker motor?

[sanddrag]

I'm not sure what I'm going to do with it. Anyway, I pulled out my handy dandy calipers and it looks like way back when I made the shaft I made it to .744 That's not going to work for a 3/4" clutch bearing to grab on. Is there any way to salvage this shaft without having to remachine a new one? Can I coat it in epoxy and then re-turn to .750? Will this work for the clutch bearing to grab on? Or will something like this work? http://www2.towerhobbies.com/cgi-bin...&I=LXJC35&P=ML I just don't know how I'd attach the spinner cone to the shaft though.

Or maybe it would be best to just figure out a way to mount the engine from the back so I can use the stock pull starter.

[jrocket567]

Originally Posted by sanddrag

Or will something like this work? http://www2.towerhobbies.com/cgi-bin...&I=LXJC35&P=ML I just don't know how I'd attach the spinner cone to the shaft though.

Or maybe it would be best to just figure out a way to mount the engine from the back so I can use the stock pull starter.

that starter is used for RC airplanes.. theres a plasticy concave fitting on the output shaft that fits into the convex propeller hub... it should have enough torque to turn over that small engine, but getting the starter to fit onto the shaft will probably be the hardest part of using it.. good luck

[team222badbrad]

From TowerHobbies (the best RC site in the world!) it appears that the airplane starter shaft is keyed.

I was browsing through the link you gave us and it appears that there are different adapters.

Here is what was leading me to think it was keyed:
http://www2.towerhobbies.com/cgi-bin...?&I=LXJC36&P=V

So you could probably make something other than the propeller cone adapter!

I would not use epoxy. I do not know the melting point of epoxy, but chances are it may melt.

I would make a metal sleve insert if possible.

I am not exactly sure what you are trying to do with the under cut shaft so I can't really help you much.

[Hunter]

you can also braze the shaft bigger and then turn that down to .750. We do that all the time to get tight fits.

[sanddrag]

Today I redid my mounting plate with a jig saw and dremel so that it can still mount to the front of the engine but the pull starter will still fit on too. The engine casing remains wholly intact. On the front of the plastic housing, there is one area in that is used to clamp the engine onto the trimmer tube. I am going to use this clamping hole to hold a long bronze bushing. I will make a new 5/8" shaft that is turned down small on the end, then milled square so that it can fit into the square hole in the engine shaft.

Now that I have the mouting, starting, and shaft figured out, I need to know: What should I do with it! I need to keep the cost very minimal. Ideas so far have been a scooter, RC car, or generator. The generator idea is good but I wouldn't use it enough. A scooter would be cool but I already have a minibike. An RC car would be totally awesome but the big servos would be expensive. Any other ideas? Maybe a blender for promotional events like team fundraisers? Will it run verticle or will the carb "load up." Also, I'd have to route the exhaust away.

As a side note, I played with the engine quite a bit today. It is quite small and has quite low compression. It's cool, I can hold it in my hand and start it up and run it right in the palm of my hand! Even though it is small, it still packs some punch. When I had it sitting on the lawn and it was running while I was standing about five feet away, I could feel the ground shaking. It is a fun little engine.

[NoodleKnight]

make a hover craft. low compression you say? sounds like it can use some FORCED INDUCTION!

[sanddrag]

Originally Posted by NoodleKnight

compression you say? sounds like it can use some FORCED INDUCTION!

I had thought of "charging" it. I don't think there is enough exhaust pressure/volume to turbocharge it, but I definitely think supercharging would work. I could just stick an air hose from a compressor in there but I'm afraid I would blow the engine. I wouldn't want an electric blower because that is just cheesy, it has to be crank driven. I know I have seen it done on a little RC nitro engine before, but I can't find the pic anymore.

Does anyone know of any links or pictures or articles on small (RC, weedeater, lawnmower) supercharged engines? Thanks.

Hovercraft is a good idea, but wouldn't I need two engines, one for lift and one for direction? Or would I just duct some of the air from the thrust fan into the air bag/skirt?

Another idea I just came up with is an air compressor. I know where to get a tank, but I don't know where to get an air "pump"