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What's the Flywheel for? (Read 583 times)
DragBikeMike
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What's the Flywheel for?
06/18/18 at 23:58:54
 
I have seen that a number of members have installed a lighter flywheel.  I was thinking that it might be possible to completely remove the flywheel.  It's a huge rotating mass.  What doe it do?  Why is it there?  It weighs over 6 lbs.

Getting rid of that huge rotating chunk of steel should:

-Improve throttle response

-Permit the engine to accelerate faster.

-Reduce gyroscopic action and allow the bike to be pitched around easier.

-Improve compression braking

-Reduce the overall weight of the bike.


Getting rid of that huge rotating chunk of steel could also:

-Make the bike impossible to start (flywheel inertia overcomes compression).

-Make the bike difficult to ride (hard to get rolling in 1st.)

-Make it hard to maintain a steady speed.

-Make the bike rough at cruise (jerking back & forth).

-Possibly cause a vibration issue.


That big 6+ pound flywheel stores a lot of energy.  The old "a body in motion tends to stay in motion" theory.  Removing it entirely might upset the apple cart.  From what I could gather, most of the folks using lighter flywheels are lobbing off about 2 lbs.  Hey, if a little bit is good, lots must be better.  I wanted to see what would happen if I turned the flywheel into a spacer.  So read on and see what I found out.
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DragBikeMike
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Re: What's the Flywheel for?
Reply #1 - 06/19/18 at 00:16:37
 
I disassembled the left side of the engine.  You can use a 36mm open end wrench to hang onto the alternator rotor while you impact off the bolt.  I found out that 36mm offset wrenches are pretty hard to come by but 36 mm combo wrenches are a dime a dozen.


To hold the flywheel while I removed the 46mm nut I fabricated a simple tool using 3/16" bar stock and a couple of spacers.  You could even stack up a bunch of washers instead of using spacers.  It's important that the connection be rigid.  I had purchased a 46mm socket but I would have had to chop it in half and convert it to a deep socket.  Also, it was a 12 point socket and you really need to use a 6 point since the nut is so thin.  I surveyed my old tool bin and found my old Harley pulley nut socket.  It's 1-7/8" and plenty deep, so instead of struggling with a big socket chop-up and weld job, I epoxied six .030" steel shims into the socket to do a quick conversion from 1-7/8" to 1-13/16" (46mm).  Worked like a champ.  Here is a pic of the simple tool & modified socket.
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DragBikeMike
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Re: What's the Flywheel for?
Reply #2 - 06/19/18 at 00:20:13
 
Here is another pic of how the holding tool is installed.  The bosses on the frame for the footpeg work perfectly to restrain the tool and prevent the flywheel from turning.  It's super easy to fabricate the tool.
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DragBikeMike
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Re: What's the Flywheel for?
Reply #3 - 06/19/18 at 00:27:59
 
The flywheel weighs 6 lbs. 0.2 ozs.  It is a little over 6-1/2" in diameter.  Initially I thought I could simply replace it with a spacer, but after closer examination of the assembly it became apparent that this beast forms an integral component of the starter drive.  I didn't want to create a problem with the flywheel nut continually backing off so I opted to "chance-um" and machine down the original flywheel, thus retaining the splines and preventing any undesirable rotation during starting.  Don't want that big nut comin loose.   Here's a pic of the original flywheel and starter gear.
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DragBikeMike
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Re: What's the Flywheel for?
Reply #4 - 06/19/18 at 00:39:50
 
I made a spud to mount the flywheel in my lathe.  Since this is part of the rotating assembly, you want to maintain concentricity and perpendicularity as you machine away the unwanted material (at least I hope it's unwanted).  Optimum runout would be .001" TIR or less but I used a threshold of .002" TIR.  That seemed reasonable since I was removing almost the entire flywheel.  If you plan on only removing an inch or so, then stick with a max OF .001" TIR.   You don't want a shaker.  Setting it up in a 4 jaw allowed me to zero it right in.  Here's a pic of the spud.
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DragBikeMike
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Re: What's the Flywheel for?
Reply #5 - 06/19/18 at 00:51:17
 
Man, hacking off 3-1/2" of solid steel is a BIG job on a tiny Chinese lathe.  But it can be done.  I had a problem maintaining surface finish.  At first, things went really nice, but as the diameter reduced, the cut became hard, sparks flew, tool bits disintegrated.  I'm thinkin maybe my tool bit height was higher than it should have been.  Any machinists out there got any ideas.  As the diameter reduced it got harder and harder to maintain a decent cut.  I tried increasing the rpm to maintain surface speed but it only made things worse.

Here is a pic of 5 lbs of machining chips.  Lots & lots of work.  Hey!  I'm retired.
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DragBikeMike
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Re: What's the Flywheel for?
Reply #6 - 06/19/18 at 00:56:01
 
I took the flywheel down to exactly 3.000" diameter.  As I mentioned, surface finish was a problem but I wasn't worried about a fracture resulting from some sort of defect.  The diameter was reduced to a point where that would no longer be a factor.  There was essentially no more rotating mass.  It was simply a spacer at this point.  Here is a pic of the finished flywheel (spacer).
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DragBikeMike
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Re: What's the Flywheel for?
Reply #7 - 06/19/18 at 00:59:45
 
In order to reinstall the beast, I would need some way to hang on to things while I tightened the flywheel nut.  I fabbed out a clamp assembly to use in conjunction with my cheapskate flywheel holder.  It worked perfect.  I tightened the nut to 110 ft-lbs. with no slippage.  Here is a pic of that tool.
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Re: What's the Flywheel for?
Reply #8 - 06/19/18 at 01:01:42
 
Here is a pic of the installed 3" flywheel (ummm! spacer).  It's obviously a BIG change.  Hope this wasn't a mistake.
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DragBikeMike
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Re: What's the Flywheel for?
Reply #9 - 06/19/18 at 01:23:28
 
Well, how did it work?  It started right up.  No issues with flywheel inertia.  It idled exactly the same.  It had pretty much the same throttle response.  Shoots, I was expecting big league WhaaaapAhhh and got the same old vroom vroom.  It drove off a stand still pretty much the same, maybe needed a bit more clutch-work to get it rolling.  Felt pretty much the same on surface street roll-ons.  What's up?  Six pounds less rotating mass and essentially no change?  

On the freeway, 55 to 75 feels much smoother and quicker.  Here's the kicker, "smoother".  The WOT acceleration at speed is "smoother" & appears quicker.  I would have thought the flywheel would have kept the acceleration smooth, but it feels smoother now, and feels quicker.  The whole deal defies logic.  I was expecting enhanced throttle response in neutral, but it feels same.  I was expecting jerky operation but it feels smoother.  I was expecting driveability issues but its pretty much the same as before.  How do you lose 5 lbs of rotating mass and have almost no change in driveability?


I ain't much of a road racer so I can't comment on how it flicks around, but let's face it, if you nullify the 6 pound gyroscope spinning around right at axle level things gotta flick better.  


Compression braking feels about the same but I'm not in to breaking the rear skin loose with a downshift.


Bottom line, the mod works OK.  No need to worry about screwing things up.  It starts and drives pretty much the same, and acceleration appears to be better and smoother.  You will lose about 5 lbs of curb weight.  It should flick better due to reduced gyroscopic action.  It's all good.


So, why did the OEM put this thing on the LS650?
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justin_o_guy2
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Re: What's the Flywheel for?
Reply #10 - 06/19/18 at 02:22:10
 
That's not the report I expected.


Is it worth doing?
Do you see a net gain?
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Re: What's the Flywheel for?
Reply #11 - 06/19/18 at 02:50:00
 
I have been cutting the flywheels down for Dave to sell, but not that much. I stop where the threads are so that the flywheel can be removed and installed easily.
Interesting that cutting it down as far as you did didn't change the manners much.
Heavy flywheels hide a lot of problems, and generally make drivability a bit more relaxed. On Ducatis, I knock a few pounds off the flywheel and the bike revs faster, turns easier, and feels faster. There is an aftermarket aluminum Duc flywheel that weighs ounces. More than a few folks installed them, then went back to steel as the low end running became too jerky.
Others love them.
BMW from the late 60's to the early 80's went thru a few incarnations of flywheels, eventually ending up with one so light they stopped calling it a flywheel, and just call it a clutch carrier. You can feel a significant improvement in ability to rev, and a definite increase in vibration as the flywheels got lighter. I think the last incarnation are too light. My '91 buzzes so bad at speed the mirrors are useless.
So, that's why I settled on knocking a few pounds off the Savage flywheel, but not all of it.
Thanks for the pics and the report!
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Re: What's the Flywheel for?
Reply #12 - 06/19/18 at 03:54:21
 
DragBikeMike wrote on 06/19/18 at 01:23:28:
It should flick better due to reduced gyroscopic action.  It's all good.

So, why did the OEM put this thing on the LS650?


We affectionately refer to this item as "flickability" on this forum......and the result is a small grin whenever we get the chance to use our new word.

I have one of Armen's "small" flywheels on my bike right now.  I had a medium sized one from the first batch on last year.  The medium size one resulted in about a 1/2 second reduction in the 0-60 mph time - I really could not tell any difference in the feel of the bike.

Why did Suzuki use this large flywheel?  My guess would be that they wanted the bike easy to ride and tough to stall when letting out the clutch.....it provides an aid to the new rider.  When you look at the rotating mass of the crankshaft, electrical rotor.......and the counterbalance shaft that spins twice the engine rpm - there is a lot of rotating inertia and does make you wonder why they also put a large flywheel on the bike.

If you look at the color of the flywheel, it appears they induction hardened the spline area.  As you machined the flywheel and got close to the center, I suspect you started to reach the metal that was hardened.    
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Re: What's the Flywheel for?
Reply #13 - 06/19/18 at 05:45:32
 
Interesting results. Not what I would expect based on previous experience (not with a Savage).

When I was a kid, I knew a guy that was into motocross. He had a 175cc 2-stroke bike with some pretty wild cylinder porting and the flywheel removed. It was almost un-rideable. Hard to get moving without stalling. instant throttle response (up and down) made it feel like the throttle had only two positions-- on and off. When it hit the power band, the bike just leaped forward and you would hope you could hang on and keep the front wheel down.

Maybe the added heft of the Savage vs a small motocross mitigates some of the harshness of not having a flywheel.
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Re: What's the Flywheel for?
Reply #14 - 06/19/18 at 05:50:04
 
bobert_FSO wrote on 06/19/18 at 05:45:32:
He had a 175cc 2-stroke bike with some pretty wild cylinder porting and the flywheel removed. It was almost un-rideable. Hard to get moving without stalling. instant throttle response (up and down) made it feel like the throttle had only two positions-- on and off. When it hit the power band, the bike just leaped forward and you would hope you could hang on and keep the front wheel down.


The difference likely is more related to rotating mass/inertia.  The motocross bike had a small crankshaft spinning - and the electrical rotor was also small and light as it only needed to make enough power for the ignition.

The Savage has a very large/heavy crank, electrical rotor and counterbalance shaft......I am guessing the combined weight of all those items is close to 20 pounds!

Who on this forum is brave enough to relive the days of the BSA Goldstar.....and remove the counterbalancer shaft?  (Stock up on threadlocker). Wink
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