Flywheel Weight

[brian r]

Can any one give me a ball park idea on how much weight should be added to a little motor that revs more like a MX bike than a trials bike?

[copemech]

BRIAN,

It has to do as much with cyl. porting as flyweight. A engine has to have the torque to spin up the additional weight or it will perform worse than it did before you added the weight. Classic case is the little gasgas 70/80, you just have to spin it fast to make it go.

If you must experiment, don't go over 1/3 to 1/2 lb at a time.

Cheers

[jaylael]

Brian: You didn't say what sort of little motor you are referring to. On the Hodaka 125 trials specials we typically fabricate a three pound weight to add to the stock flywheel. This results in just enough flywheel for trials.

[brian r]

Jay, it's a Mecatechno Amigo with a Morini Franco Motori.

It's 80cc's and it has some weight (1.2 lbs.) on the flywheel already.

It's still too peaky though if you ask me. I see my son constantly spinning the real wheel in sections.

Thanks Hanna.

Edited January 16, 2004 by Brian R

[copemech]

then add a 135lb Beta 80!

[jaylael]

I haven't had the pleasure of working on a Mecatecno Amigo, but I suggest you increse the flywheel weight to improve it's smoothness. One limiting factor will be the room inside the mag cover. With some vintage bikes like the KT 250, you have to make a spacer for the mag cover to allow room for the weight in there. Depending on the size of the crankshaft nut, some ready made flywheel weights might go right on there. Steahly is one company which makes an array of these weights. On my old '92 Honda CR 125 the weight also contained the flywheel nut. You take off the original nut and then thread the weight onto the crankshaft. To keep it on, they use set screws which bite into the existing flywheel. Perhaps some type of steahly flywheel weight would fit on there. You'd need to measure the crankshaft stub size, thread pitch and whether or not it's left or right handed thread. I'd get the heaviest one you can. After that you might need to fabricate a spacer for the flywheel cover. Let us know how you make out. JL

[bullfrog]

Another Hodaka trials special rider weighing in here. Mine has 3.5 lbs of flywheel weight added to the stock magneto flywheel - and it feels pretty good. Please do post your final solution, I'd be very interested in reading about the weight you add and how it works for you.

Ed

[brian r]

We'll let you know. It looks like the case has a pretty good amount of room in it.

The brass is just sitting over here on the floor waiting for me to start something. The brass is 6 lbs. right now. I'll get it so that it fits the case and

on the flywheel first and just see what it weights then. 3.5 pounds sounds like a good start to me. Probably a little heavy but it's easier to take brass off than it is to put it back on!

Edited January 23, 2004 by Brian R

[charliechitlins]

Remember...the closer you get the weight to the outer edge, the more it will do.

[tonyp884]

I kinda have the same problem. My son's 1999 Beta Mini Trail 50 which is actually NOT a Beta but is made by Trueba in Spain. It has a Moto Morini 50cc S5-GE engine. This is basically an MX engine. I'd love to have some port work done or add some weight to the flywheel. So, my question is, how do you add weight to a flywheel? I thought about stick on wheel weights, but figured that would not be enough.

I'd appreciate any help.

Tony M. Powers

Charlotte, NC

[alan bechard]

Tony, you fit a brass sleeve over the flywheel is a common way of doing it, or ring if you will.

I do not think you want to do that on your whatever though.

With the centrifigul (sp) clutch, it will effect too many things, like how long it takes from throttle roll on to engagement.

With a clutch bike, you can overcome some of the limitations put on by additional weight, but with the automatics, there are some extra twists.

[tonyp884]

Thanks for the info Alan. hope you're doing well. We are about to go outside and ride the Beta. I've setup a little section in the yard, real tight. Trying to teach Matthew to hold his head up and look where he is going, not watch his front tire so much.

It is 22 degrees outside, 1 inch of snow and about a 1/2 inch of sleet on top of that with more freezing rain today. All that white on the ground looks really cool with the colored ribon on the section.

Matthew said he needs to practice ! At least he is willing!

Have a good day,

Tony P

[charliechitlins]

I wish I knew more about 2-stroke porting, but I seem to remember a trick involving increasing the volume in the intake tract to increase low end.

This was done by getting the carb farther from the reed.

Sometimes a piece of radiator hose cut to size will do it as a replacement for the stock compliance fitting.

Part of the problem is that these little engines usually work great at alarmingly high RPM's, and not too many kids are willing to turn the wick up that far.

[brian r]

Well, it's done. 3.2 lbs. Seems to have slowed the reving quite a bit. Jordan hasn't riden it yet to see what the results are. I'll get back to everyone on how it works for him.

[brian r]

Well, we rode some on Saturday and he still has no problem with spinning the tire. Most of that problem comes from the tires and throttle control though. It was a bit slippery on the notorious TTC loop, in fact it snowed all day. I think it was an improvement and I'm waiting to see how it works in the dry. Hopefully some time soon he will move to a full sized bike and I think that the lack of traction will go away. I also got a tip to go to only 2lbs. of air in both tires instead of the 4 in rear and 5 in front that I like to use. All in all I think it was an improvement and it's easily reversed back to the way it was.