Topic: Lightened crank VS No rotor.

[754]

How much weight comes off a lightened crank?

When I build my engine this winter I think I will leave the crank heavy. ..may balance though.

Anyone lighten the cranks themselves?

I have at times run no alterator rotor, amazing difference, espescially in down braking. If I run the bike on the salt, I can take off the alternator  for a few days, it saves like 4 or 6 lbs.

Another idea I have been looking at is a 650 nighthawk system I have, It could be run 2 ways;

Custom cover, would end up somewhat like a CR cover, would llok cool.

The other way, remote drive. That is a pully mounted on the crank plus a seal plate, then a belt running to the charging unit behind the cylinder and over the starter, I see that they used this to narrow the newer motors (Nighthawk & CBX). Mainly though I think it would look cool to have the mag on 1 side and belt drive alt on the other. But one huge Benefit if you fit an idler is, you can in a minute back off idler and remove belt,,, instant lighter rotating mass!!

Just an idea, but it really sounds like it would be worth it... all machining I can do myself..

[fuzzybutt]

just lightening the rotor can shave 3 pounds according to ken at the cyclexchange. on a street bike they dont recomend running a lightened crank as it can be entertaining to say the least, launching a bike with a lightened crank as you hjave to rev it fairly hard and slip the clutch to get it rolling.

[sparty]

just lightening the rotor can shave 3 pounds according to ken at the cyclexchange. on a street bike they dont recomend running a lightened crank as it can be entertaining to say the least, launching a bike with a lightened crank as you hjave to rev it fairly hard and slip the clutch to get it rolling.

Fuzzybutt,

My bike has a lightened and balanced crank and it is a blast to ride.  I notice nothing different about starting out.  Where did you get your misinformation?

Sparty

[seaweb11]

Have not yet experienced the lighter crank............yet!!!!     

The new build has one though   Can't wait!

[MRieck]

 I have a lightened crank in my CB and FJ1200(now 1314). I have installed them in a few bikes with no problems.

[754]

What Fuzzy is referring to is less flwheel effect. Yes a lighter crank can lead to choppy running at low speed/rpm, but I am way used to grabbing a handful of R's and slipping the clutch to over come that... That and launching at 7 or 8 K..lol.

Motors with little flwheels can be hard to ride, with alternator removed you would swear the brake got tapped when you roll off the throttle, but that is about 6lbs off..

[Jerry Rxman Griffin aka MuthaF'er]

Lightened crank and rotor are 3lbs each

[Sam Green Racing]

Our bike has a lightened crank with the end removed where it comes out of the main bearing into the generator housing.

It is an 836 with a mild cam, ported head, CR31s, boyer ignition and a 4 into race pipe.

It is still as tractable at low speeds as it was with the stock motor, wind it up off the line anywhere near 5000rpms and you have a smoking tyre for 20 yards then a massive wheelie at about 50 yards when the clutch goes fully home.

If you want to race your bike as well as ride it on the road, build yourself another motor, it's no use taking a barrel of lard to the salt flats

Sam.

[fuzzybutt]

i got that from ken at cyclexchange

[MRieck]

Lightened crank and rotor are 3lbs each

Is that 3lbs off the OLD style rotor Jerry? I have cut some newer rotors down and didn't get anywhere near 3 lbs off.

[754]

I think 3  or +lbs comes off early one with the flange, in 73 Honda started using lighter ones..

 Ok now I am Quoting from a RC catalog, which shows a stock heavy one and a lightened one, here is the text;

3 3/4 lb alternator to replace stock 8 1/2 lb unit. Helps to prevent crankshaft breakage. Charging system is not altered. I deal for street racer who needs a charging system but wants performance. Lets engine rev, more quickly and safely.
 Comes completely balanced.

#1093 Deletes electric starter

#1094 With starter ( recommended for small motors only)
                                          core charge 50.00

 I am not planning on drag-racing only on my motor and would rather  spend cash to make the bottom end bulletproof. Plus I have the covers made to run no alternator, it is easy to whip off, with a greater weight savings than a lightened crank.

 Now something about Bonneville that many people misunderstand.. it maybe the only form of racing where weight is not critical...in fact it is sometimes added to gain traction.
On the long course (only place you can set a record), you have 3 or 5 miles to get to speed, weight of the crank makes no difference.

Bikes like Busa's often fill the swingarm with lead shot in an effort to get traction.

I want to lighten the crank later  but not for next summer, I can cut it myself and rebalance the crank..

[Sam Green Racing]

754, before I try to put an answer to your problem, can you figure why my bike runs 13.5 seconds over the quarter mile on concrete airfield runways and can only run 14 seconds on a fully prepaired dragstrip?

Sam.

[MRieck]

 Rick Stetson said he came off the line better with the heavy rotor. It hurt the crank but the hardest drives were with some weight.

[Sam Green Racing]

That's right Mike but why the half second slower on a surface made for the job of accelerating on ? (using the old stock motor)

Sam.

[sparty]

That's right Mike but why the half second slower on a surface made for the job of accelerating on ? (using the old stock motor)

Sam.

Must be glue on the track Sam.  How about headwind?  Temp.?  Humidity?  They can all play a factor.  My new engine ran great today in the cooler temps.  The new oil also helps.

[754]

Sam What was used for timing Equip at each place.. Dragstrips are pretty accurate, other timimg methods??

Also some strips are altitude correct and are not giving you exact time, it is time you would get if you were at sea level.

Altitude and temp can affecrt your times, especially if it is tipping away from your current jetting..

A dragstrip time  against another racer is two components  To trip the lights)added..your reaction time + ET.

If you chassis is not reacting as it could you will have a lower time. Then there is roll in/roll out (your position between the stage lights) it can affect your ET as well.

 Lots of variables, a bit of a learning curve.. I had a great teacher my landlord/neighbor had a rail and coached me a lot..

[Jerry Rxman Griffin aka MuthaF'er]

Mike,
I have a 75 and a 78 rotor. I'd love to see a picture of both with weights. I believe I got the 3lbs from an article on the RC Cobra engine so that would've been an older rotor probably. I'd like to think that also includes the loss of the starter clutch. I've seen one RC rotor and it looked half the size. Looks like you'd need to cut down the side cover so the rotor would fit inside the stator to get much charging.

Sam,
I always thought that concrete gave better traction? At least fresh concrete anyway. Would the difference be due to the amount of rubber laid down previously & during your run? 

[Sam Green Racing]

I think 3  or +lbs comes off early one with the flange, in 73 Honda started using lighter ones..

 Ok now I am Quoting from a RC catalog, which shows a stock heavy one and a lightened one, here is the text;

3 3/4 lb alternator to replace stock 8 1/2 lb unit. Helps to prevent crankshaft breakage. Charging system is not altered. I deal for street racer who needs a charging system but wants performance. Lets engine rev, more quickly and safely.
 Comes completely balanced.

#1093 Deletes electric starter

#1094 With starter ( recommended for small motors only)
                                          core charge 50.00

 I am not planning on drag-racing only on my motor and would rather  spend cash to make the bottom end bulletproof. Plus I have the covers made to run no alternator, it is easy to whip off, with a greater weight savings than a lightened crank.

 Now something about Bonneville that many people misunderstand.. it maybe the only form of racing where weight is not critical...in fact it is sometimes added to gain traction.
On the long course (only place you can set a record), you have 3 or 5 miles to get to speed, weight of the crank makes no difference.

Bikes like Busa's often fill the swingarm with lead shot in an effort to get traction.

I want to lighten the crank later  but not for next summer, I can cut it myself and rebalance the crank..

OK, here's what I am trying to put over.
The CB hasn't got the power to overcome the prepaired surface of a dragstrip.
Start upping the bhp and you will eventually overcome the surface that has been put down for the bikes and cars that have an abundance of power.
This is where you start having problems with your set up. There are several ways round these problems but as a drag racer that had a good teacher, you probably know what they are,  lead weights being just one of them.
On the salt flats the problem is more or less in reverse.(talking your CB now not a Busa or any other big powerfull bike) Your power is down due to the altitude so where can you find a bit more power ?  When you tune to make more power, you change the bikes power to weight ratio, allowing you to pull a higher gear and go faster. If you don't tune but reduce the weight instead you are still changing the bikes power to weight ratio which will also allow you to pull that higher gear. If you agree with this, then why not loose weight off the bike wherever you can.
I ran a small bike in the 60s that had a top speed of 70mph. It would never pull peak revs in top gear because Mr Honda made it's top gear to high.
I reduced the weight enough to allow it to pull that high top gear and it recorded 87.5mph (a 25% increase).
Lots of people think that reducing weight only affects acceleration but in reality it can aid top end speed.
If on the salt you have 3 miles to the first timing trap you wouldn't need to worry about wheel spin because you have all the time in the world to build up to your top speed.
It's down to you what you do but the lighter you can get your bike the better.
Good luck in your quest for speed, tell us more of what you are hoping to achieve.

Sam.

[Sam Green Racing]

Mike,
I have a 75 and a 78 rotor. I'd love to see a picture of both with weights. I believe I got the 3lbs from an article on the RC Cobra engine so that would've been an older rotor probably. I'd like to think that also includes the loss of the starter clutch. I've seen one RC rotor and it looked half the size. Looks like you'd need to cut down the side cover so the rotor would fit inside the stator to get much charging.

Sam,
I always thought that concrete gave better traction? At least fresh concrete anyway. Would the difference be due to the amount of rubber laid down previously & during your run? 

I'm talking a prepaired track Jerry where they spay the surface with traction compound, it's that sticky it makes you legs ache trying to walk on it.

Sam.

[754]

The Question on the topic was, why bother lightening the crank if  I remove the rotor to run it  at a race.

Then I went on to mention that weght is not as important on the salt in fact it can help (on this I was not referring to the SOHC but in general terms mostly re bikes over 150 mph and streamliner.very fast & very heavy)

The sticky track ( back to drag racing) is because it is Sprayed with VHT. Very High Traction.. If you have extreme traction and are not prepared/used to it and you bog you will lose time..

[Sam Green Racing]

The Question on the topic was, why bother lightening the crank if  I remove the rotor to run it  at a race.

754, forgive me if I can't understand what you are trying to achieve, why do you want to remove the rotor/generator to run in a race, am I missing somthing ?

Sam.

[754]

Quicker response, depends on what you are using it for though. I have the covers made up, and a shaved down shifter cover, ran them before on an ice racer..

I would like the lighter crank, but will concentrate on getting good rods..finally and leathers, and other things that are nandatory..

[Sam Green Racing]

Ok, so you know it makes sence removing the genny to get quicker responce, so why don't you lighten the crank while you have it out for balancing. You said you could do the work yourself, so why do half a job ?

Sam.

[kghost]

Surface texture....

Was the runway grooved to prevent hydroplaning as many are?

Was it rough textured? Runway concrete often is.

I'd bet you could get 1/2 second back if you coated the whole track with COKE syrup.