RZayas

My Feedback: (2)

I have a weedeater engine that a coworker of mine gave me and I want to experiment with it. I would like to get the opinion of some of the folks here that have done conversions. First of all, how do you lighten a flywheel? All that I have seen and read in the very limited research that I've done looks like whoever does one of these conversions, shaves off the fins on one side of the flywheel and a little bit on the other side. I ask myself, what about drilling holes on it? That would certainly lighten it and as long as you balance the flywheel back after you cut & drill it, it should be "OK", right ?!?!?! Which takes me to my next question, how do you balance a flywheel? Do you have a jig for it? I don't think you could use a prop balancing jig ! HOW? ? ? The next thing I would like to do, and I think only one person suggested it in one of my previous postings, and it is to open the exhaust and intake ports up to let the engine breath better. How do you go about doing that? Does one just drill out the ports? What do I need to watch out for? Oh before I forget to mention, I'm already thinking about going the EI way since it reduces the weight by about a pound and you wouldn't have to mess around with the flywheel. So the engine porting would be inline with it. So if by now you haven't realized it, I would like to make this little engine "SCREAM".

Antique

My Feedback: (4)

Flywheels are best left alone, or just the fins that stick up above the flat part...flywheels are cast from cheap pot metal and usually carry a warning, something like "any alteration can cause bursting"
Good advice....

RZayas

My Feedback: (2)

[sm=confused.gif] Well, isn't that what these guys do when they cut the fins. I would like to know if anyone has ever bursted a properly balanced one ? [sm=72_72.gif] Anyone?

Antique

My Feedback: (4)

Somebody on here had one come apart, maybe he'll see this....

Ryobi Coyote

RCIGN1's advice is the way to go. Unless you have a safe way and/or place for testing such a modification of a flywheel, be very careful! Or try electronic ignition.

Consider the following: More than twenty-years ago, Dario Brisighella,Sr was “overbalancing” Quadra flywheels. This was a “sweet-spot” unbalancing of the flywheel, in order to reduce overall engine vibration. Dario claimed that this one mod reduced vibration by 75 percent and increased speed over 800 RPM! However, as a former kart racer, he had access to an engine-testing lab, and perhaps the equipment to safely spin-test a flywheel (at well over redline, 15 or 20K RPM), in a test chamber.

Then there was the fellow who thought he could save a few bucks, by doing his own “overbalancing” on a Homelite. At a fun-fly, he was wowing the crowd with low passes and snap rolls – really wringing ‘er out. Oh,oh…what was that? The front of his plane came off! He lost the flywheel, prop, spinner, and cowl, leaving the plane tail-heavy and out of control. The plane came down in the spectator area, narrowly missing a family. They searched for weeks, but never found the flywheel! My best guess was that the flavor of his “sweet-spot” was causing some kind of harmonic vibration, which led to the failure of the crankshaft.

R.C..

Rcpilot

My Feedback: (78)

Thats the best kind of engine. FREE!

Your off to a good start. The guys in this forum know all there is to know about conversion engines.

Thats right. You put it in a lathe and trim off the fins that stick out past the face of the magneto. But thats ALL. It's been done--but it's not advisable to take out all the fins down to the backplate of the magneto.

Don't do that. You'll end up with an exploding magneto. Bad idea.

Use this to balance it:
http://www2.towerhobbies.com/cgi-bin...?&I=LXD712&P=7

You buy or build a degree wheel first. You document the intake duration. Document the exhaust duration. Document the transfer port duration. How do you know where your going if you don't know where your at? You have to know what kind of porting is there in the first place before you can grind it out and pump it up.

NO!!!!!! You'll screw it up. It takes a tungston carbide bit and one really steady hand to grind on a cylinder.

Stuff like grinding through the side of the cylinder trying to open the ports up too much. There is only so much material in the ports. You can only grind it so far before you poke a hole in the side of the cylinder. Paper weight.
Squish band clearence. Less is better. A lot less will make a nice bang, but only once.
Compression ratio. More is better. Too much leads to detonation and preignition.
Exhaust duration. More is better. Too much ends up causing all kinds of problems. Some of those problems can be handled with additional porting in other areas or even a tuned pipe. Most of those problems mean you ruined it and overported it.

Then why are you worried about balancing the magneto? You don't need a magneto with EI.

Have fun. They only "scream" for a couple hours run time. Then they pop. Just not strong enough.

You can make them run better than stock. A LOT better than stock. But, at some point, longevity suffers. If you have a surplus of engines--then port and squeeze untill you pop a couple. It's actually quite fun to blow one of them up. Unfortunately, the plane doesn't always survive back to the runway after the engine pukes it's guts all over the flying field. Something about a tailheavy plane being really hard to fly..........................

Some of the things I posted here may prompt more questions. The answers to some of those questions you may have can be found in this forum and also in the gas engines forum. Just do a search in these 2 forums. If you still have questions after reading the search results we'll be happy to help out.

I don't know how extensive your knowledge of 2-stroke engines is. I can't assume that you know what "duration" and "squish" are. If you already know, then your well on your way to having some serious fun. If not--then the search function is probably the best place to start.

Now get out that degree wheel and start writing stuff down!! [8D] Modifying engines is best done methodically and with lots of notes. It takes a tremdous amount of patience, time, documentation and knowledge--but when you are successful at it--it's really gratifying.

ZAGNUT

My Feedback: (1)

anyone remember the guy with the 18,000 rpm ryobi a few years back?

if you really want to keep the ignition magneto but also want to save some weight then look into getting the system used on the zenoahs. someone here is selling them for cheap, probably leftovers from conversions to battery ignition.



dave

RZayas

My Feedback: (2)

I started working on the engine last weekend and decided to do away with the flywheel (that's after I tried a couple of new bits on my Dremel) and magneto all together after reading a few of the replies so I'm going to skip the part on the flywheel, although it would be interesting if I could to get material properties and calculate the forces on the flywheel and create a model of it on the computer and analyze it to see where and how much can be taken off, and determine a threshhold RPM for one of these little engines before it "explodes". I would be surprised to see it get up to 12k RPM after you put a prop on it.


Definitely I have to write down everything, and NO I will not drill.

Sorry that was before I grounded of the supports for the magneto [sm=bananahead.gif]

Definitely I am going to slightly modify the exhaust port, and shape the intake port to the slightly bigger new carb that I got. I got myself a couple of books on engine blueprinting and building, that even though they are more geared towards a Chevy engine should give me a good idea about head porting and polishing.

Thanks for your reply we'll see how it goes![sm=49_49.gif]