Started working on HRCA#1's flywheel tonight....
Interesting, his was a bight different starting weight then the other 4 I've had. They have all been within 3/8 of an oz.. but all different.
HRCA#1's started 1/4 oz lighter then mine did.

 

This one did not come out as light as previous one as I was asked to stick to the Rodger Ditchfield specs vs taking as much off as i can.


Just finished up, and ready to pack back up in a box for mail in the morning.
Over all I was able to remove almost 1 lb

 

This is such an awesome mod for this bike. Marquez, thanks for pics.

 

overall,what does this do for the bike,if its stock motor or built up some.

 

Takes it from Vro o o o om
to Vroooooooooooom

 

lol,so im guessing quicker on the take off,faster to red line,but lose some engine braking due to loss of mass?

 

It picks up RPM's quicker and has more compression braking.

Now that said, I have not tried one of the 1lb version like this one is.....

Mine is 5lb 15 1/8oz version.

 

dam,thats a lot of weight off it.i was thinking of just going with a 1lb off.
are they balanced after you are done,or is it better to get the whole system balanced together.

 

Not that much less, mine is 5 5/8oz less then this one.......that last 1/4 " or so is what makes the difference.

No not re balanced... It does not make a noticeable difference. If I had a place local that could do it for a decent cost, i'd have um balanced, but i don't.

 

all correct but the engine braking... you GAIN engine braking due to the loss of mass.

 

ohhhh ok,i got it,it makes sense.

 

Flywheel#4 boxed and on it's way back to it's owner.

 

Actually, it increases the engine deceleration, but not the ability to engine brake. You need mass and inertia to engine brake, at least as I understand it.

 

Just the opposite.
Newton

A engine in motion, tends to stay in motion

SO an engine that has x mass has y engine braking.

That same engine with LESS mass (lighter flywheel) will tend to stay in motion LESS ie have MORE engine breaking..

Same reason the engine with less rotating mass will spin up faster.

 

HRCA#1 Your box is in the mail , but i screwed up..it's always been my policy to return the used, broken, or replaced parts when I give back the item I worked on.

Please let me know if you want me to send yours... I'll get it in the mail come Tuesday .

Should fit in a USPS MED priority box ...

 

No thanks Erik, you can toss it in your recycle bin. I want to thank you for the great service and more than reasonable price.

 

Actually, you both have a point here... Neither are really wrong...

Less mass means the engine will stay in motion less, ie "more" engine braking... But as the engine has less mass to put vs the rear wheel as well when it is infact braking, the engine braking actually becomes "less" forceful to some extent... This is a very minor change here, so not a big noticable differerence, but it's there...

So the end result is a snappier engine with shorter spool up, a quicker engine braking, but still less intrusive as it comes on softer...

 

Tweety that makes sense. I keeps thinking of my early Jeep with its 75 pound flywheel, and the incredible amount of engine braking it had.

A quicker and shorter engine braking with the lightened flywheel.

 

Waited till this morning and a clear head to respond as i wanted this to make sense.

Tweety..

I understand where your coming from here but I think, based on the only empirical evidence I have......

There is MORE breaking force generated with a lighter flywheel..

Yes the rotating components have less mass, but that less rotating mass allows the compression of the motor, and the closing of the air intake to effect slowing of the motor (kind of the definition there of engine breaking for a gas engine-Engine braking occurs when the retarding forces within an engine are used to slow a vehicle down)>chain>rear wheel and overall the bike.

My evidence..
simple,, regardless of any physics lessons to be had here.
the bike with the lighter flywheel, SLOWS DOWN QUICKER from a given speed when the throttle is closed.

As the only thing I changed was flywheel mass, the quicker slow down of the entire bike can only be attributed to that change.

This is very noticeable .. in back to back tests.

Not scientific at all, not a physics lesson, but simply.. the lighter flywheel bike slows faster when the throttle is chopped then the heaver flywheel bike.

I could be off on the specifics of how and why, but the what is quantifiable and measurable by simple on bike testing.

 

Marquez, this is a great thread. Thank you for your input and testing. Once the snow begins to fall in my drive way, this is something I will definately work on.
Snow.... you know the white thing that falls from the sky..

You guys down south never have to worry about that ****...euh...excuse that fowl language

I agree with you on the theory of masses. I'm in the karting world, and we play alot with this in our racing engines, and even on the karts themselves. It does make a difference in time engine acceleration. Much easier to see on a dyno, then to explain the whole thoery.

 

Ahh, my back yard last winter

 

, in that case, you must be in the northern region of Texas.

The dog still doesn't understand what's going on I'm sure.

 

I'm a little out of my area.

I think we are missing a distinction. You are correct, the engine is decelerating faster/quicker. However, it's due to less rotating mass. It's not really braking much. When I think of engine braking, I think of a diesel with a jake brake, where you can here the engine doing the braking.

I'm looking to understand, so in this case, not being contrary for aurguments sake.

I do know, since I have this modification, that the engine spins down quickly, but doesn't offer much in the way of engine braking when trying to slow down.

 

Actually, I think you misunderstood me a bit... I never said that a bike with a lighter flywheel didn't slow down faster... That is 100% true and is not up for dispute in any way...

However, you are missing the simple explanation... The bike is slowing down faster not becuase of more engine braking, but becuse of less inertia maintaining speed... Ie, the engine braking is actually the exact same amount, since the mass of the pistons and the rest hasn't changed...

If the engine braking was in fact increased as the flywheel was reduced, you would probably be at risk of locking up the rear end rather frequently, as you would be compounding the effects, ie loss of inertia + increased engine braking = loss of traction...

So, the engine braking is the same amount, but occurs/ramps up faster on a closed throttle, and there is less inertia to counteract it, so the effect is larger as a total, and as how you and I percieve it... But the force applied is actually the same...

The simple analogy for this is a bike that stops better with the exact same brakes when you lighten it a couple of pounds... Same amount of braking applied, less weight to stop...

 

+1 Tweety, I had a '73 R75/5 with a flywheel of @ 10 lbs and after Reg Pridmore drilled more than 100 holes and rebalanced, it weighed in @ 5.2 lbs. The spin up or down was "quicker", but I felt no change in engine braking.

 

depends whether you consider flywheel as part of engine or not. Following this logic, you cannost say engine revs up quicker with lighter wheel.

 

Actually, yes I can... It does so for the exact same reason... Not that the engine is making more power, but because there is less mass and inertia to overcome to accelerate the engine... Which would be the opposing argument, ie that a smaller flywheel would make the engine produce more power, same as increased engine braking...

 

Flywheel Starter Clutch Fly Wheel Magneto - 2003 03 Honda VTR1000F SuperHawk 996 | eBay

A little more then I like to pay but................

 

Actually that's a few bucks less than I paid for mine.

 

That should burn quite nicely no?