Jump to content

Different look at flywheel weight reduction

Recommended Posts

So around December my bike decided to call it a season as I use it to commute and I was planing to ride it till first snow. But I didn't make it. At around 20,000 miles (I low sided in street and lost my speedo) my engine decided to back up its magneto bolts(I know I should've done the lock tight fix when I first got the bike) well anyway. I was planing to do it during the winter but I didn't make it. Well anyway it wrecked my stator new one costs 400. Being in high school and interning doesn't leave me much time to make money other then side jobs so I found a used one on Craigslist tested it with multimeter and it tests fine.

Moving on I had to take off the magneto to extract the bolts I had to remove some weight off of it while it's out. I couldn't find much info or get any ideas where to remove some of the weight. That lead me to remove some weight off of that ring that's behind it when're magneto is attached to.

Since it's really small I had to find another way to take that 11.5 oz off ImageUploadedByThumper Talk1458491848.038314.jpg

I figure that the only way that ill accomplish this is to make it out of lighter material to not sacrifice any structural strength. I decided to go with aluminum alloy 7075. I found a decent price online for $14 for a round rod 5 inch in diameter and 1inch long because if I got any less it would be same price and thinker pice was easier to mill down

I'm lucky enough to have a Freind who's in charge of machine shop so he took care of that part and I ended up with thisImageUploadedByThumper Talk1458492959.556164.jpg

4.5 oz for final weight next would be to take some weight off of the flywheel when money comes around but I'm also putting on a fcr 37 to add more to the snap I'm looking for on the street and in the woods for the weekend. If anyone has any input I'll be happy to hear. I just though I'd share this because I really didn't see anything like this before or any approach like this. As of questions that anyone might have I'll be happy to answer or add anything that I have missed

  • Like 3

Share this post


Link to post
Share on other sites

Looks like a good idea and some nice machining but I would be a little concerned about the softer aluminum that's surrounding the starter clutch paws. Let me know how it holds up.

  • Like 1

Share this post


Link to post
Share on other sites

A lighter flywheel for woods riding is the wrong direction to go. If anything, woods riders ADD flywheel weight to make low speed riding more tractable and smoother. Light flywheels are a SuperMoto-Road Racing deal where you are doing 10,000 rpm shifts and have to faster revs and drops to match speeds.

As James says, the starter rollers may well dent that ring and 'catch' though hard anodizing might make it survivable.

The FCR 37 for tight woods riding is a better choice than a 39. Though when you think about your flywheel mod and the carb, they sort of go against each other in logic.

  • Like 4

Share this post


Link to post
Share on other sites

Looks like a good idea and some nice machining but I would be a little concerned about the softer aluminum that's surrounding the starter clutch paws. Let me know how it holds up.

A lighter flywheel for woods riding is the wrong direction to go. If anything, woods riders ADD flywheel weight to make low speed riding more tractable and smoother. Light flywheels are a SuperMoto-Road Racing deal where you are doing 10,000 rpm shifts and have to faster revs and drops to match speeds.

As James says, the starter rollers may well dent that ring and 'catch' though hard anodizing might make it survivable.

The FCR 37 for tight woods riding is a better choice than a 39. Though when you think about your flywheel mod and the carb, they sort of go against each other in logic.

That is a good point of the jaws eating the ring. Looks like the oil maintenance will have one more task. For at least couple times until I can judge the wear. So while I'll ride the "bare" one I'll have another one anodized if that won't helped I'm thinking of a pressed on ring. I'll just have to see how the metals react together when heated so they expand somewhat in uniform rate.

About the weight reduction for not being the best for woods I agree but my Drz is bone stock other then the coming fcr and 3x3 mod but my planes with that is to put smaller sprocket on the wheel to make it more highway capable to travel between school home and other places and to still have the throttle response for logs rocks or other obstacles and techniques. But I understand where your coming from. And in the worst case I would be too much weight taken off I can always go back since it's a 4 hour job from start to finish taking time your time

I apologize for my English as it is not my first language and thanks for reading and your input regarding this mod and an update will definitely come as I put the bike to together today and how it handles in dirt somewhere around Friday and my next oil maintenance.

Share this post


Link to post
Share on other sites

So I got my bike up and running ( it took me a lot longer then I was planing it wood) everything was awsome except for the fuel screw started to vibrate out( I need to go up on pilot jet) well anyway I was banging t around for a while about 4-5 gas tank after completing my bike and playing around the town on it between commutes their was a moment where the starter slipped on start up. That happens to me very rearly on the factory one so I didn't think anything of it. I kept riding it but in the next 3 days I lost the starter completely where even helping it with a bump didn't help it at all. When I got to the garage and took it off their was 1-2mm rig where the starter clutch ate the aluminum away. So an oil and filter change was done and it looks like majority of it came out. The only plus side of this is that now I know this isn't good for commuting (about 8 starts a day lasted 4-5 weeks). So it held fairly well for the amount of abuse I throw at it. But I'm not sure if it was worth it considering that the rest of those shavings are floating around the engine but it's at least aluminum so it's soft right lol. Well anyway I put back the stocker with great pain and you can defemetly feel the difference between the 2. Keeps traction better if your aggressive with the throttle but I defemetly want the weight off of their. So like I said shaving the flywheel and I'm debating on what to press in that ring where the clutch grabs that's semi light is as hard as stock and won't loosen up or stretch the aluminum when heated up a bit

Share this post


Link to post
Share on other sites

Already cleaned it and did my best to flush the engine with some oil

 

 

Sorry, "frame" screen was the wrong terminology. I'm referring to the screen inside the engine itself.  That screen can't be cleaned well without splitting the cases.

Share this post


Link to post
Share on other sites

 Being in high school and interning doesn't leave me much time to make money other then side jobs 

 

 

I apologize for my English as it is not my first language and thanks for reading and your input regarding this mod and an update will definitely come as I put the bike to together today and how it handles in dirt somewhere around Friday and my next oil maintenance.

 

Off topic, but I wanna throw you a thumbs up for being an articulate high schooler with great English.  I wouldn't have guessed if you didn't mention either.

Most high schoolers ramble all over the place, and most US high schoolers can't construct a sentence as well as you do.

Keep it up.  You have a bright future.

Share this post


Link to post
Share on other sites

Pick up oil screen is located below the oil pump.  If you remove the oil pump, you can back flush the screen.  If I had seen this thread earlier I would have warned you off  the aluminum sprag clutch ring.  Never going to work.  Hard anodize in this case is not the answer ether.  Substrate just will not support the load.

Share this post


Link to post
Share on other sites

Yes but not hard like like hardened steel.  No carbides for wear resistance. It would last longer than aluminum but not for long.

Share this post


Link to post
Share on other sites

I though I replayed earlier and it didn't send. I back washed the oil screen like Nobel mentioned little bit came out so I'm hopping most of it was trapped by the oil filter. Did an oil change after a 100 miles or so and didn't see any shimmer. So It means it just build up somewhere or grinned down to nothing and didn't cause too much damage. Well anyway today I hit around 1000 miles and will do an oil change to make sure the stuff is out as much as passible. Followed by another early oil change. This deffenetly though me a lesson. I never realized how much power the clutch ring transfers. And I can't believe the diffract it made. I heard trail tech has one made a light weight flywheel for the Drz. So it looks like I'm looking for a used one of those or if I find a place that can shave my down. One or the other some weight has to be lost

Anyway thanks for the replays and advice it did not go to waste. This was an awesome learning experience. We learn from out mistakes the most after all right. But anyway if I'll have any problems raising from this ill let you guys know. For now thank you

Share this post


Link to post
Share on other sites

heavier flywheel, smoother engine. smoother engine, better traction.

Share this post


Link to post
Share on other sites

heavier flywheel, smoother engine. smoother engine, better traction.

So how heavy is is Ideal? 

 

What does Honda run?

 

What does KTM run?

 

What does Yamaha run?

 

What does Johnny Walker run on his XC300?

Share this post


Link to post
Share on other sites

Heavier flywheel = slower engine revving and lower max rpm. It keeps the engine smoothly rotating at low idle rpm.

Lighter flywheel = faster revving and high top rpm. At the expense of being easier to stall and requiring a higher idle.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×