Modifications - Performance Discuss aftermarket and DIY performance modifications

Lightened flywheel

Old 05-19-2008, 05:44 AM
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Lightened flywheel

For those of you who haven't, it is completely necessary. It made absolutely no difference in "driveability", and made a big difference in power delivery. I would say that you could go well beyound the 1/2" that was recommended to me. The weight portion is .9" roughly, and I took around .5". You could easily go in the .7-.8" range. BIG DIFFERENCE, well recommended.
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Old 05-19-2008, 05:53 AM
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Originally Posted by autoteach View Post
For those of you who haven't, it is completely necessary. It made absolutely no difference in "driveability", and made a big difference in power delivery. I would say that you could go well beyound the 1/2" that was recommended to me. The weight portion is .9" roughly, and I took around .5". You could easily go in the .7-.8" range. BIG DIFFERENCE, well recommended.
Could you please explain some more. Also, if you have pics, that would be cool.
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Old 05-19-2008, 06:04 AM
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I unfortunately did not have the time to take any pics, as well as my camera was stolen recently. As for an explanation: Honda, for one reason or another, put an extremely large flywheel on the superhawk. as an example, the Sv650 uses the stator's magnet "basket" alone as a flywheel, the superhawk uses that plus a 3/4" thick, 6"+ diameter chunk of steel as a flywheel. I merely machined off a 1/2" of the diameter of the steel chunk. I may go back in over the winter for more.
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Old 05-19-2008, 06:05 AM
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+1 on more info this is very interesting, the SH have a pretty high engine inertia, but I was afraid that the engine would stall or jerks around 3-4k, have you reset your TPS to 500 ohms ??
Edit : It's probably to avoid the hard low rpm stalling since it has a lot of compression, so you mounted it on lathe and shaved some off, did you had to rebalance the FW assy ??
This could make a world of difference on a tight track to follow the other supermachines, way more than an exhaust could ever get

Last edited by gboezio; 05-19-2008 at 06:10 AM.
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Old 05-19-2008, 02:25 PM
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can any machine shop do this? where'd you get it done at? what do you tell them you want done? "take of half inch and balance if need be"
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Old 05-19-2008, 02:35 PM
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yes yes more info please!!!!
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Old 05-19-2008, 02:43 PM
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Mikstr has also done this mod with good results I believe.
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Old 05-19-2008, 07:31 PM
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is it 1/2 inch off diameter or radius?
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Old 05-19-2008, 07:34 PM
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Diameter. I'm not sure you could take .5" off the radius and have anything left.
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Old 05-19-2008, 07:36 PM
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Originally Posted by killer5280 View Post
Diameter. I'm not sure you could take .5" off the radius and have anything left.
Well, I would have screwed that up badly if I had jumped too quickly.
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Old 05-19-2008, 09:51 PM
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As I'm sure autoteach knows, lightening the flywheel will allow the engine to gain revs quicker, but also lose revs quicker which means if climbing a hill at somewhat low revs you will need to downshift sooner. With the gobs of torque the SH has this may not be a problem, but if lightening it, a little at a time would be best.
My first bike in 1981, a used 78 CX500 bought from a Honda tech, had a lightened flywheel and other mods which made it lighter and a one of a kind first bike for the canyons. But it only had 50 hp to start with. The SH has more than I can use riding on the street stock. When twisted to the stop, it gets up there fast enough for me, but maybe I'm just old.
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Old 05-20-2008, 05:48 AM
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Ummm, I meant I took a 1/2" off of the radius, an inch off the diameter!! HAHA There is way more material. I could have gone a full 1.5" with leaving enough material to support the starter gear assembly. As for what I did with the machine shop, I said to myself, "self, take off a half inch!" and that is what I did. I am a high school teacher, with machine shops and such, so I did it myself. You should be able to take it to a machine shop, tho, and they should be able to do it. As for the balancing, this is the second one I have done. The first was a '80 SRX snowmobile, which had a balnced flywheel. We machined it and saw no difference in the balance. The superhawk flywheel is purely machined (besides the stator portion) and has no real balancing signs whatsoever. I made sure that I had the runout within .001-.002" and called it a day. any more questions??
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Old 05-20-2008, 02:55 PM
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Originally Posted by autoteach View Post
The superhawk flywheel is purely machined (besides the stator portion) and has no real balancing signs whatsoever.

I was going to do this the last time I had mine apart. I didn't because my flywheel DOES clearly have balancing holes drilled in it. They are significant enough that I was scared to machine it. It's not vibrations that you feel as a rider that I'm concerned about, it's those higher-order vibrations that break cranks.

I'd love to do this, but I think I'll leave it alone for now.
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Old 05-20-2008, 03:46 PM
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I'm no expert, but it seems to me that the more you reduce mass the less balance would matter. Not to say it would become irrelevant, but maybe just not as important.
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Old 05-21-2008, 01:35 PM
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Since the lightening holes (on mine at least) are not equally spaced around the circumference you are removing an unbalanced amount of material. This, by definition, is throwing off the balancing of the part. That part I'm sure of, the part that I don't know is if this would cause any problems. I guess the bottom line is that I'm too afraid to dive in without knowing for sure.

Has anyone contacted Roger of Revolution Racing about this? If anyone would know he would. Maybe I've still got his e-mail address somewhere....
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Old 05-21-2008, 01:54 PM
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Any pictures of the before and after product?
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Old 05-22-2008, 05:57 AM
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someone stole my camera, so nope. As for the balance, mine had no holes drilled in it. It wasn't balanced by adding or removing material, and I took off an equal amount of material all the way around. As for balance, we put the first one on the balancer, and it was inconclusive to "balance". Any time we made a change, it just did the same thing, unrepeatedly. So, we called it a day. Now, i do agree that they should be blanced, but I dont have the means necessary, the directions from other forum members didn't include it, and it would give me a reason to rebuild if it blew up.
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Old 05-23-2008, 11:03 AM
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The unbalance creates a 1X (at rotating speed) vibration. There are no harmonics created, because it is a simple synchronous imbalance. Rubbing, or impacting would created harmonics, imbalance does not.

The flywheel is close coupled to the crankshaft journal bearing (not much overhang). The crank is very rigid, because it has to be strong. So the bending of the crank is minimal. the worse thing that a minor imbalance would cause is a synchronous vibration transmitted to the chassis. I never noticed one.
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Old 05-23-2008, 11:19 AM
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For example. Let's say the engine produces 75 ft-lbs of torque at the crank. the actual torque is averaged (aidied by the flywheel), but lets say the instantaneous torque applied to the crank is 75 ft-lbs, as a very conservative estimate.

The engine has a stroke of 66mm, or 2.6 inches, or 0.22 ft.
75 ft-lbs is about 340 lbs at the rod journal. All of that is transmitted through the crank webs to rotate the crank.

I don't think I'm going to worry about a few oz-inches of imbalance!

I would be more worried about excessively lightening the flywheel. !/2 inch off the diameter is the tested number I used.

Last edited by RCVTR; 05-23-2008 at 11:22 AM.
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Old 05-23-2008, 11:32 AM
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A1/2" made a lot of difference in the accel but very little in starting ability or in idling. I truely believe that you can go more, possibly .75, or 1.5" off of the diameter.
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Old 05-23-2008, 11:36 AM
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The Hawk is notoriously slow revving, largely because of the heavy flywheel. I have heard it mentioned (probably from RCVTR) that the RC51 flywheel is significantly lighter. How much lighter is the RC flywheel than the Hawk's, and I also wonder about other liter 90 degree twins like the SVs, TLs and Ducatis. Anyone know?
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Old 05-23-2008, 11:56 AM
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ths sv650 doesn't have the weight attached, it is just a magneto basket.
http://www.promotorsportsinc.com/fic...ion_detail.asp
magneto for the 650
alternator for the shawk
alternator for the Rc51

Both the sv and rc have no counterweight. Makes me wonder how much you could take off.
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Old 05-23-2008, 06:36 PM
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Bill, I think you are right about being able to lighten it more. There seem to be two camps, based on what I've read and gleaned from conversations. One camp looks at low-speed, off-idle behavior and wants to go as low in rotating mass as possible. The other camp looks at the ability to aggressively put power to the ground. The test results I based my lightening on was in the second group. Testing with a highly modified race engine. Going too light on the flywheel causes the engine to want to spin up more aggressively, causing the rear tire to spin. For a street bike, with a stock, to lightly modified engine, it would not be an issue. I can't claim to be in the second camp, that's just where I got my recommendation.

Regarding imbalance, I need to clarify and attempt to quantify the potential force cause by imbalance. I think my flywheel had 3 balancing holes. I'll estimate them at 0.20" diameter, 0.25" deep and group them all together. When I do that I get a wieght of about 0.1 oz. of steel. The holes were at a radius of about 3"

If I take that mass at that radius and spin it at 10,000 RPM I get an imbalance force of about 53 lbs. Not an insignificant number, but not enough to worry about stress on the crankshaft. The imbalance rotates with the crank , so there is no stress cycling on the crank itself. The firing of the cylinders produces a much higher vibration, so I think the imbalance from the flywheel is not noticable. When you decrease the diameter of the flywheel you may also decrease the amount of imbalance
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Old 05-24-2008, 03:59 AM
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Originally Posted by RCVTR View Post
Bill, I think you are right about being able to lighten it more. There seem to be two camps, based on what I've read and gleaned from conversations. One camp looks at low-speed, off-idle behavior and wants to go as low in rotating mass as possible. The other camp looks at the ability to aggressively put power to the ground. The test results I based my lightening on was in the second group. Testing with a highly modified race engine. Going too light on the flywheel causes the engine to want to spin up more aggressively, causing the rear tire to spin. For a street bike, with a stock, to lightly modified engine, it would not be an issue. I can't claim to be in the second camp, that's just where I got my recommendation.

Regarding imbalance, I need to clarify and attempt to quantify the potential force cause by imbalance. I think my flywheel had 3 balancing holes. I'll estimate them at 0.20" diameter, 0.25" deep and group them all together. When I do that I get a wieght of about 0.1 oz. of steel. The holes were at a radius of about 3"

If I take that mass at that radius and spin it at 10,000 RPM I get an imbalance force of about 53 lbs. Not an insignificant number, but not enough to worry about stress on the crankshaft. The imbalance rotates with the crank , so there is no stress cycling on the crank itself. The firing of the cylinders produces a much higher vibration, so I think the imbalance from the flywheel is not noticable. When you decrease the diameter of the flywheel you may also decrease the amount of imbalance

sounds like the crank bearings may take a beating,from the imbalance.
im not to worried about the crank with stock horsepower.
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Old 05-24-2008, 12:26 PM
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I don't think it's much to worry about, when you compare it to the force from the rods. The rod force is actualy much higher than the numer calculated using the nominal torque.

Also, the imbalance force goes up with RPM squared. It's only about 13 lbs at 5000 RPM.
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Old 05-24-2008, 04:51 PM
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is their anyways to balance a flywheel weight?
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Old 05-25-2008, 02:31 AM
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Yes, an engine workshop/builder should have the tools... probably gonna cost you though...
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Old 05-25-2008, 05:43 AM
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Achieving a zero balance is not quite expensive, nothing close to a V8 or V6 crankshaft that need a lot of measuring and bob weight attachments and then balanced to zero.
Any shop who are rebuilding driveshafts should have the proper equipment
Balancing a V8 crank can cost from 200 to 300 bucks
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Old 05-25-2008, 09:33 AM
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If you don't mind spending the money you can do it yourself.

http://www.bhagwansons.com/gifs/stand.jpg

This is the type of equipment that is user to balance grinding wheels in a machine shop - it's also what some people use to balance engine rotating assemblies (flywheel/crank/clutch/etc in automotive and moto applications).


As for lightening holes - if you drill holes in the side of the flywheel you need to make sure they are equally spaced (even number of holes around the flywheel). This would result in not altering the balance of the flywheel too much, but .....


Keep in mind that this is steel (at least it should be) and it may/may not have voids or heavy spots within it. While you may do your best to keep everything good you can still do damage, long term and probably minor (but i'm assuming here, of course), so don't get too greedy if you can't check balance before and after.


I have a few of questions that i'd like input on, if any don't mind .....

1) would holes drilled in the side of the flywheel affect electricity production? If so, how?

2) how about an aluminum flywheel? Would aluminum still produce what's needed to have the assembly produce electricity?

PATIA!

I can't find flywheels on Ron Ayers for a price reference - what do these things cost new?
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Old 05-25-2008, 09:55 AM
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I've been bothered by the amount of imbalance I used. The numbers I used were of the top of my head. I believe if you had a 50 lb rotating force at 166HZ, you would feel it.

So I redid the numbers using 2 0.15" dia holes, 0.25" deep. Then I get about a 20 lb. unbalance force.

When I did mine, 0.5 off the diameter did not completely remove the balance holes. And reducing the diameter should improve the balance, if the flywheel is carefully chucked in the lathe and runout is minimal. As I stated before, there was no sign (at all) of a balance problem, when I ran mine.

If the alternator rotor is the primary source of the imbalance, it's not going to get any better by lightening the flwheel.

The flyweel is independent from the function of the alternator.

Aluminum probably would not have nearly enough mass to make an effective flywheel.
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