Reducing Flywheel Effect

[dogger315]

New guy here with a question.

A little background info first. I'm in the early stages of an engine
build that will be used in an AF conversion for MX. I read the post
on the CR250 ignition swaps and have decided to use the ignition
from a 2000 CR250 (mostly because I already have one). I also
want to send the crankshaft to Crank Works for balancing and
lightening.

I raced the CR500 back when, and along with power-on-demand,
I remember the vibration, head shake and reluctance to turn.

I figure the crank balance will help with the vibration and the AF
conversion with the better suspension available today will help
with the headshake. I'm hoping by lightening the rotational
assembly, it willl help the managability and turning.

The question:
Does anybody know if these lightening efforts have produced any
negative "side effects", i.e. tendency to stall in tight corners, more
abrupt power delivery, etc. By abrupt, I mean a Suzuki TM400
style powerband

Any help or insight is appreciated.

dogger

[Tharrell]

Can't help you with that but, get the Sidi's. ha ha ha
btw-What year 500 did you race? I ask because my old '85 vibrated a lot but my 92 is smooth as silk.

[AlisoBob]

On the 85', its more of a "power impulse" , than a vibration.

When you chop the power, the "vibration" quits....

[Roostius_Maximus]

i know the pipe shutter on my '88 was very bad, til i icut the bridge out and changed how it ran, now its almost stil, kinda like it got balanced, but nothing got changed

[Nodge]

I cant keep my hands on the bars unless the throttle is wide open on my 85 motor. Havent tried out my new flexx bars yet......

[NightBiker07]

lightening the rotating assembly will make it more "peppy" and violent. heavier will smooth it out

[dogger315]

What year 500 did you race?

I raced them from 1990 to 93. I'm posting a picture of my '93.
The vibration level for all my 500s was only high when compared
to a 250; not objectionable, but not welcomed toward the end of
the moto.

I have done some nosing around since my original post and
it looks like crank balancing is a waste of time on a single
cylinder motor and lightening (as has been pointed out), is
not a good idea either.

I plan to build the motor from a stock '01 bottom end except for a
'92 transmission. I have a JD dual map programmable ignition
left from my '01 CR250 spare parts stash which I think will work
fine for this application.

The new question is, does anybody have recommendations for the
best cylinder/head combo for MX?

dogger

[/quote]

[seanmx57]

The only way to know if the crank is smooth is run it. 2 identical new cranks and one can be great and the other can be so bad it cracks cases and frames. Been there on the bad one and herd about good one.

[gregrobo]

i never got to ride mine in the steel frame but in the aluminium frame its silky smooth can ride it all day and thats a standard crank guess i got lucky

[M.F.D.B.]

I think with all the tinkerers we have here we could get some experimenting going on vibration dampers (attached to the frame spars?) Something of the viscous style like high end V8 harmonic balancers?

[2strokeforever]

thats extra weight

[thestuz]

if youve got the 250 ign, use it.swap it back if you dont like it.
its pretty simple to swap them over if you have a flywheel puller.
with mine, it didnt make a noticable difference in how the bike handled but it did make starting a hell of alot easier and seemed to reduce the midrange spike in the powerband. kinda made it more ridable.
once you hook it up, youll see how much brighter the spark is.
let us know what you think.