Balancing motor

no_crf50_here · Feb 1, 2009

I'm about to pull down my motard motad motor AGAIN and just interested in finding out if anyone out there has done it. I'd perfer first hand experience not what your 12yr old mate told you at the skate park!!!

So....

1. Ever done it?
2. Where to get it done? Brisbane area.
3. HP gains or just realibility?
4. Do you just drop your bottom end off and pick it up when done or ?
5. Worth replacing bigends while i'm there?

Thanks... 16hp here i come!

Cactus Jack · Feb 1, 2009

Balancing requires an experienced person who has done lots of similar engines ... I know how multi cylinder engines are done but single cylinder engines require a different approach ... Basically , it's best to only replace pistons , rings and gudgeon pins with items that are the precise same weight or slightly lighter than stock ... NEVER heavier ...

Here's a link explaining what's involved ...

Balancing Small Engines by ET Westbury: Page 2

And a few others ...

Engine Balancing

Engine balance - Wikipedia, the free encyclopedia

Cactus Jack · Feb 2, 2009

[Secondly, there is a vibration produced by the change in speed and therefore kinetic energy of the piston. The crankshaft will tend to slow down as the piston speeds up and absorbs energy, and to speed up again as the piston gives up energy in slowing down at the top and bottom of the stroke. This vibration has twice the frequency of the first vibration, and absorbing it is one function of the flywheel.

Thirdly, there is a vibration produced by the fact that the engine is only producing power during the power stroke. In a four-stroke engine this vibration will have half the frequency of the first vibration, as the cylinder fires once every two revolutions. In a two-stroke engine, it will have the same frequency as the first vibration. This vibration is also absorbed by the flywheel.]

Reading the above info ... anyone with a decent IQ and an engineering understanding can easily see that the speeding up and slowing down of the crank will translate as "chatter" between the primary drive gear and the clutch basket gear ... the flywheel dampens that chatter out if it's heavy enough to rotate at a constant speed ... A light flywheel can't do that ... just how they speed up rev up and rev down by putting up less resistance , they ALSO fail to resist the chatter created by pulsing ... with the result that the clutch and transmission gears get chattered to hell ... It's WELL documented in countless engineering articles that such chatter can bust crankshafts , clutches , gearbox gears and drive trains ... Lightened flywheels are a double edged sword ... you gain performance at the sacrifice of reliability ... Engine designers aren't idiots who put flywheels on cranks needlessly ... they put the weight there because it greatly increases engine life and some engines cost thousands upon thousands of dollars to repair ... plus down time can destroy a businesses success ie earth moving equipment , buses , trains etc ...

Of course , pit bike engines are cheap and easy to replace so most racers don't mind the added cost and loss of reliability in exchange for greater performance ... but some dork heads expect too much and blame the failures on inferior engine parts ... most of those people are phonies with no formal engineering or mechanical training ...

no_crf50_here · Feb 2, 2009

Agreed - they are cheap and easy to replace. Was just looking for that edge.

I'm a firm believer in spending good money on a good result. I've done extensive youtubing (and your links) on the subject in the past few hours and I agree that balancing will be a waist of money/imposible

I'll just put the new piston & head in run it up on the dyno and tinker some more and see if i come up with the goods.

If I get a 16 HP dyno sheet, it'll be framed

Thanks for your time Cactus