Hello,

Iwant to pull the magneto coil from an old homelite 25cc engine that has been converted to RC flight and replace it with an electronic ignition. Need some tips on how to proceed. Iknow where Ican get theelectronic components and what to do in general,except for one thing :What do Ido with the old flywheel? It has not beenmachined or anything and itwouldbe nice to get a newone with less weightbut if Icant find one, will the magnet that is currently embedded in the fly wheel fire the CDI ignition hall effect sensor at the right advance time? It has an aluminiumhub of sorts that is screwed on to the engine shaft. I could potentially put a magnet there but how can Iget the right position for the magnet?

Thank you in advance for your replies.

Ranga

I think that wackerengines.com has the parts to convert a engine over for you. They have Homelite engine conversion parts.
You basically need the prop adapter hub, a CDI unit with the timing sensor and magnet.

They use a small neodymium magnet with the sensor. The flywheel magnet is too big.

Basically you find top dead center. Then using a degree wheel, locate a convenient spot for the magnet and sensor. Maybe mounting the sensor first. Then place the magnet so that the sensor is about 28 degrees before top dead center (BTDC) as the magnet passes it. The sensor triggers on the trailing edge as the magnet passes by.

Yeah; www.wackerengines.com, www.lambertsrc.com, or www.carrprecision.com.

The prop hub for the CDI electronic ignition replaces the heavy magneto flywheel. A sensor is mounted on a large diameter hose clamp that clamps to the front bearing snout of the crankcase, and you can rotate it to set the timing.

I made the parts for my Homelite engine shown in the pics. Just posted them to let you get the idea how it works.

AV8TOR

Av8tor, very nice. Your picture gave me some good ideas. Where can you get the little magnet that goes on the hub? Is there a "minimum diameter" for the hub where the magnet mounts?

Another (unrelated)question. If Iwere to remove the exhaust bridge, Iwould need to "pin the piston" to prevent the ring from rotating. How easy is this to do? Ican get a ring from Frank Bowman but he says he does not have the time to pin the piston. Isuppose Icould attempt to grind a notch inthe existing ring (Is this advisable?). What tools are needed to replace the piston ring?</p>

A couple of unrelated followon questions related to your picture (but not to my original question) :

You have a connection from the top of the carb to what looks to be a crank case vent (the red tube ). What is that?

Is the velocity stack on your setup positioned the way it is supposed to be when the aircraft is flying?

Thanks

While there is no theoretical minimum diameter of the magnet hub, it should be a hub with a diameter that is near to the diameter of the front bearing snout. That's because the sensor mounts to that snout, and the sensor needs to be quite close, (.020 to .040" more or less), to the magnet. A good magnet diameter is around 1/8" or 3/16" and you can get magnets from lots of sources online. K & J Magnetics is one.

You want to use a piece of music wire or hard steel to pin the piston, and the pin diameter should be the same as the width of the piston ring land. You drill a hole in the piston several thousandths of an inch smaller than the pin, and then put a thin coat of JB Weld on the pin and carefully drive it into the piston. You must be very careful to locate the pin in the piston so that when the piston is in the cylinder, the pin is located in an area that does not have any ports that the piston ring crosses. (Transfer and exhaust ports) You then VERY carefully grind the pin down so that it is halfway down in the piston ring land. This is where the notches in the ring go, over the top of the pin, which is only half the depth of the ring land. If you don't have the pin ground down enough, it will hold the ring out a bit, and you will break the ring when you go to assemble the engine, and/or it will be pushing the ring out against the cylinder wall, which you do not want. It's too bad Frank is too busy to do this piston mod operation for you as it is a bit tricky. I definitely recommend getting a new, notched ring from Frank Bowman. Your original ring is undoubtedly worn, and Frank's rings are the best. His will come already notched for you, and most engines respond with a power increase with Frank's rings. Not to mention easier starting and better overall running. The ring gap spec on this engine is .003", which is about the width of a piece of paper. Your ring gap is undoubtedly much larger than that, and that costs power. As they say, "Never try to hop up a worn engine!"

When I hop these engines up, I do a special mod to the intake manifold, and enlarge the ports. When I do so, the pulse hole for the pulse that operates the fuel pump in the carburetor gets very close to the intake tract, or in fact gets broken into. I fill the pulse port in the manifold adapter with JB Weld, and then provide for an exterior pulse to operate the fuel pump in the carb. That is the line on the engine in the picture that you asked about. As far as the velocity stack, yes, that is the way I recommend installing it; with the larger opening to the rear. People often think it should go forward to get some ram air effect, but the truth is ram air only gives about 1% more power at 100 mph, and usually causes problems with accurate carburetion. You don't want ram air.

Well, long post but I hope it answers all your questions. Here is a link to a post I did several years ago about hopping up a Homelite 25cc: http://www.rcuniverse.com/forum/m_26...tm.htm#2621860

Good luck and have fun,
AV8TOR