Lightening flywheels

[gpercivl]

Lightening up the flywheel does improve the peak horsepower output of the motor and allows it to gain rpm more quickly but at the cost of losing a little mid-range.

My F2 bike runs Yamaha race kit ignitor and pickup which has very little mass compared to the alternator pick up it replaced...it also originally had the starter motor gear removed off the other end of the crank. The motor was very peaky and in an effort to get some mid-range back we put the starter gear back on...this lost 1 to 2 hp on the dyno, but did improve the mid-range.

A lot depends on your riding style...Dave Cole who originally raced the bike use to keep it spinning at max revs everywhere, whereas us more mortal plebs prefer to have the revs a little lower coming out of corners so the mid range is of benefit especially on NZ race tracks having relatively slow corners and short straights between.

[Motu]

If you are using an inertia dyno,which is what most bike dynos are - then yes you will see a HP increase...if you put it on a brake dyno,eddy current or the combos that are around,then no,you won't see a HP increase.An inertia dyno,or incar computer dyno measures acceleration and computes HP from that,if your bike accelerates better then it deems it has more HP,this makes you happy,but in reality no HP has been gained.

[Racey Rider]

Side issue:
I having trouble getting the flywheel off my KR150.
I have taken both engine covers off, and placed sockets on both sides, but only the nut on the cogg (Clutch side), wants to undo.
Any tips?
Flywheel nut isn't reverse thread is it?

Racey

[Big Dog]

Side issue:
I having trouble getting the flywheel off my KR150.
I have taken both engine covers off, and placed sockets on both sides, but only the nut on the cogg (Clutch side), wants to undo.
Any tips?
Flywheel nut isn't reverse thread is it?

Racey

That would be locktite on yeah? I suggest application of a hammer to the end of the bolt to break the locktite.

[merv]

Have you got an impact driver and a socket that fits it?

[Racey Rider]

Still having trouble getting this flywheel nut off.
Have been attacting it with impact driver and socket but it won't undo!
I am thinking of getting a butane torch to heat it up before trying again.
Will the heat transfer ruin any seals or anything along the crankshaft?

[Dave]

Yes- that would wreck the seals. Have a look at the exposed end of the thread and see if its left hand-it may be.Assuming that its not, Then put the bike in gear and get someone to stand on the rear brake. Get a power bar or large ratchet and pipe and undo it.Once you have the nut undone- you still may need a special puller to get the flywheel off,Most of these are on a taper and need a puller to remove.
Maybe a local bike shop would lend you one if you ask.

[speedpro]

I've removed a flywheel, actually the alternator rotor, from a race bike and the differance was great. The motor revved a lot faster, up and down. One big benefit which noone seems to have mentioned was that when piling into a corner and snapping down a few gears, because of the reduced inertia the tendancy to lock the rear wheel was reduced a lot. This is due to the ability of the motor to rev quickly to match the new gear and if the rider doesn't quite get it right then the reduced inertia has a reduced effect. It doesn't actually give you any more power except what the generator might use, say <300W, but as mentioned it may indicate a bit more on an inertia dyno.

I may be wrong but I just do not see how arranging cylinders into a "V" configuration or an inline configuration can alter an engine's power characteristics if everything else is the same. The probably lighter crank and fewer bearings could affect response but the power/torque produced at any revs should be the same if the cylinders, valves, cams, etc are the same.

[Kwaka-Kid]

yeah speed you do sound right... but its just what everyone seems to say! and yes they mention shorter crank etc, umm, yeah well i will hit some of these people up on this. but even in WSBK years ago when the RC45 was in, they were only aloud 750cc V4's, yet 1000cc inlines wasnt it? maybe im wrong there too actually, hehe who knows, all i know is people say the V4's make more torque then the inlines :S

[Kickaha]

I may be wrong but I just do not see how arranging cylinders into a "V" configuration or an inline configuration can alter an engine's power characteristics if everything else is the same. The probably lighter crank and fewer bearings could affect response but the power/torque produced at any revs should be the same if the cylinders, valves, cams, etc are the same.

Had this same argument on another website,if all those things are the same,there really shouldn't be any difference in the power delivery.


We lightened the flywheel on one of my bikes with the same results as speedpro and bikes that coud previously out accelerate me were no longer able to,at the moment we have a crank in being lightened and we are ditching the flywheel all together and just building a trigger wheel for the ignition.

[DEATH_INC.]

yeah speed you do sound right... but its just what everyone seems to say! and yes they mention shorter crank etc, umm, yeah well i will hit some of these people up on this. but even in WSBK years ago when the RC45 was in, they were only aloud 750cc V4's, yet 1000cc inlines wasnt it? maybe im wrong there too actually, hehe who knows, all i know is people say the V4's make more torque then the inlines :S

Na,it was 750 fours (of any config) or 1000 twins.....
Lightening the flywheel will work great.Have a look at smaller capacity bikes similar to yours,you may find something smaller/lighter that will fit straight on without mods......I've done this on my Turbo.
The flywheel weight argument has been around for ages,In nascar for example some guys use real light one's,favouring the quicker response,and others use a heavy wheel,helping smooth power and maintain momentum.Same with drag racing,sometimes with a less powerful engine a bit of flywheel weight will give you a better launch,helping to stop the engine bogging when you drop the clutch.

[DEATH_INC.]

I may be wrong but I just do not see how arranging cylinders into a "V" configuration or an inline configuration can alter an engine's power characteristics if everything else is the same. The probably lighter crank and fewer bearings could affect response but the power/torque produced at any revs should be the same if the cylinders, valves, cams, etc are the same.

The main reason is because it alters the timing between the power pulses.A few of the manufacturers have played around with this.Yamaha's TRX850 for example (a parallel twin) uses a 270deg (I think)crank spacing to trick it into thinking it's a 90deg v-twin.Same with the RSV aprillia,a 60deg v-twin that thinks it's a 90deg v-twin because of the crank configuration(that's why they don't sound like a Hardley).Honda too experimented with the VFR400,changing it from a 180deg crank to a 360deg crank which as anyone who has ridden the nc24 and nc30 will tell you altered the power characteristics heaps.
And a few of you old guys will remember the old f5000 days when they played around with flat plane cranks in the V8's to get a little more power.....

[Motu]

Anyone who heard the Guzzi V8 last year would of been disapointed because it didn't sound like a ''real'' V8,that was the 180 or flat plane crank,it's the 90deg crank that has the yank tank sound.

The V twin staggered firing impulses giving traction has been known to the American flattrackers for a long time - the off beat impulses and a declining torque curve give great control in low traction situations,with so much power on tap with superbikes etc it has become the hot set up.My 45 deg Honda engine had a single pin crank for dirt track but a staggered 90 crank for street use - one sounded like a Harley,the other like a Ducati.

[wkid_one]

Same principal goes for the Duke big bang motor in Gp as opposed to the traditional firing of the multis. It is all about trying to find different ways of doing the same thing better (like sex I suppose).

Like the rotary engine for the Lambo that the Kiwi designed. Just about trying to overcome the natural physics of a combustion engine to make it more efficient.

[Kickaha]

The main reason is because it alters the timing between the power pulses

Well that could be done with any engine,doesn't have to be a V motor,its all to do with the crank phasing and firing order.

As an example a friend of mine with a TZ250 superkart running a 89 reverse cylinder engine has a 180 degree firing order and is quite a peaky motor,as an experiment he rephased the crank to a 90 degree firing order like the later V twin,changed ignition etc and then ran it,completely different sound and power delivery was then more like the V twin and a lot more driveable.