lightning up the flywheel

[basser23]

DeMark,
Barkers has a huge amount of Mz,SZR,Raptor experience..their exhausts
are excellent for the Sport anyway. i have spoken with Andy Weiss on
occasion at Summit Point Wva raceway...he was running his SZR..most excellent.
I am located near Gaithersburg/Germantown/Frederick...
Chip

[Kirk]

Yes the Raptor top end parts are a direct swap. I ordered a Hot Cam and Wiseco Piston for a Raptor and they were a drop in. The bottom ends are different so you need a parts fishe to compare for assurance.

[Bill Jurgenson]

HI, Lightening the flywheel and starter freewheel is the first measure I recommend, long before changing anything in the engine or using other carbs.
I do this in in exchange for the parts from the customer plus of course the cost of modifying them, That why the customer doesn't have to wait. Normally, I do it in the shop here while the customer waits and watches or helps if he wants to.
Part 1: the flywheel is turned down as much as is reasonably possible.
Part 2: the freewheel is turned down to the step and an aluminum ring shrunk on, the whole turned to the original size. The freewheel is then reground inside.
The engine revs more freely, so the bike is more responsive, especially if the owner has followed my recommendation to mount a 42 or 43 tooth chainwheel + plus the best chain money can buy(DID520 ERV2)and a 8400 rpm CDI. Besides the performance improvement, the bike also need less gas for the same kind of riding. Stands to reason since the mass of the flywheel+freewheel is not eating up HP.

[Wonky]

Hmmm! Great that you have some knowledge for us MZ guys Bill but lightening the Flywheel/Freewheel doesn't increase BHP. BHP will only be increased if you increase the amount of compression in the engine, cylinder volume, i.e a bore/port and polish. Lightening ANY parts in ANY engine just means that the engine has less resistence whilst turning over, thus meaning that the engine spins more freely. In the XT engine, for example, lightening the Flywheel/Freewheel will make the bike a little twitchy bottom end as there is less resistence from the heavier parts. This will result in a lurching twitchy throttle reponse and increasing the sprocket size will cause the use of more fuel. This approach to your XT engine before any other engine modifications would definately not be a good approach to tuning an XT engine. It would make an excellent addition to lightweight race-tuned components but i certainly wouldn't advise it as a first stop approach to unleashing power on a road tune or anything else for that matter!

[basser23]

I agree with BOTH, Wonky and Bill. To realize what hp is available stock,
and increase the responsiveness,lightening the flywheel would make sense. You are using available hp to move the bike,not spin a flywheel up.
To make more hp, the mods suggested ,ie compression,bore, cams and carbs, exhaust would be in order.
Chip

[Bill Jurgenson]

wonky wrote a bit further up:

Lightening parts will add less resistance within the engines moving components, less vibration and will help with picking up the revs. Losing weight helps with higher speed and acceleration...

Exactly what I meant!

and then went on to write following my posting:

Bill but lightening the Flywheel/Freewheel doesn't increase BHP.

I did not mean to imply it does - of course it doesn't, but that doesn't deter from the fact that the mass of the flywheel etc does use power when it is accelerated. BHP is measured on the brake at more less constant revs; once at speed to flywheel doesn't need that power to be moved, on the contrary it could even aid in giving a eversoslightly higher rating since its mass also stores some of that power it needed to be accelerated.
The point ist - see wonky's quote above - that the lightened parts accelerate faster, need less power to do so and so also need less gas to do so. This has been tested. And of course when the rider takes advantage of the better performance he is NOT going to get beter mileage. I wrote

the bike also need less gas for the same kind of riding.

Then the

lurching twitchy throttle reponse

can't be used as an excuse. There is no excuse for not learning to control that right hand. The CV carb is of course no help since it allows heavyhandedness without punishment. Change to a flatslide and quickturn grip... Or perhaps "go back to school" with a classic high-performance 2-stroke with that narrow on/off band. My Tour will idle at 850rpm if need be - with that lightened flywheel assembly and no counterbalancer. Of course there is no reason or purpose for such a low idle in real life riding.

I have done this modification to several bikes with the XTZ engine, some tuned (lightly as well heavily; my racer has no flywheel at all, much less a starter and a much lightened crank and no counter balancer but has the least vibrations of any engine I have built) and a couple not at all, including my own SZR, a stock Tour and another stock Replica. Both the Replica rider, a motorcycle journalist, and the Tour rider reported independently that the bikes were noticably quicker to ride and needed less gas. What can I say? At the time I did it to my own Tour, it was not tuned either, but the counterbalancer had been removed. I ride the thing that way and have done so for the last 45000km.

[Wonky]

Good stuff mate, you didn't have to justify what you wrote, all input is appreciated and i'm not questioning your work, just the quote that you advise Lightening Flywheel/Freewheel as a first stage of Tuning to increase BHP, which it doesn't and wouldn't, with which you have explained in your above post, no worries! You obviously have lots of experience and i respect that. We've tuned hundreds of XT engines and our best engine won us the 2000 Supermono European Championship Title, we are very proud of that and try our upmost to explain things a little less technical, we are not all engineers and sometimes what we write can be a little misleading to those not as mechanically minded, thats all buddy. Thanks for the input though!

[tuny]

bike is running again and made some rides now,
i'm impressed by the power but if there is a big difference i can not tell, what i do know is that the bike comes up better in lower rev's and seems to pickup a bit sooner after chifting up. in the summer i'l try some more, with this weather it is not so perfect, i allready crashed it's front fender on a light poal. but the bike is ok, no other damage little to crazy ont the trottle in wett conditons made a hell of a slide but did not put him down, my front fender grabed the poal an i mised it by a mm. scarry but not enough to stop me back on and directly the trottle is the best cure.

[Wonky]

Easy tiger! Take care out there buddy, make it safe.....or test on a bloody long straight road!

[tuny]

and back without bike
this weekend i'm goiing to tri and find the error, my left handlebar swich doesn't work annymore, and have no time today and tomorw so it will be saterday as i test this. hope i find it quick

[tuny]

yes yes long time but i'm back running. using my bike every day now and the most noticable difference i can find is that the bike schifts much much better in and out gear. the rest is not as spectacular as asumed but ok, i'm still satisfied i did this change and would do it again.

[cat]

my bike goes like HELL realy i can pull it up on gas in 3e gear !!! but still want more

juss! get an R6 - and put mx bars on it - take the plastic off and put mx bars.

[keithcross]

my bike goes like HELL realy i can pull it up on gas in 3e gear !!! but still want more

juss! get an R6 - and put mx bars on it - take the plastic off and put mx bars.

Or for a little more comfort, put Enduro plastics, tyres and bars on a Goldwing

Keith