What is the down side to a lighter flywheel?
Dan

 

less bottom end faster revving but not necessarily a bad thing. Could be interesting.

 

Sounds like it may be a worthwhile mod for these bikes.

Just to note; just because the assembly ID and OD are concentric, doesn't necessarily mean the assembly is perfectly balanced. I don't doubt an improvement over OEM though, since removing eccentric weight from the OD will and reducing OD will have a big effect on imbalance.

Easier to stall at very low engine speeds (not really less low end power, just more likely to stall). Less idle stability, or need for increased idle speed. Increased torque fluctuations through the drivetrain (may equate to increased wear). ...But there might be enough rotating weight in the crankshaft that it won't matter much anyway. However, for those with high-compression pistons (such as the BB351), I'd be cautious. I'm not saying don't try it, just know what you're getting into.

 

Found a little on-line. Lightening the flywheel can cause more engine vibration. Flywheel and clutch mass can mask other vibrations. You may need to adjust carb to keep engine smooth. Clutch could slip. May need to up idle speed, and keep the revs a little higher when running low rpm. Don't know how much of this applies to our KLX.

 

Here's what I found about lightening the flywheel, and this is from my own REAL experiences.....everytime I've done one for a customer the results were always positive. Less vibration, better throttle response. I've NEVER had any issues with the idle...or stalling....or increased vibration...engine reliability or anything of the sorts.
When the job is done right the outcome of the product/service shows when my costumers come back to me with a big smile on their face......need I say more?

Have a nice day.

 

This is neat, i'd deffinetely just want the flywheel trued up a bit though.

I dont think there is much negative to lightening it though either, just less energy stored in the rotating mass... i mean for all intensive purposes the flywheel is similiar to a capacitor for electrical purposes... it floats out power inputs and outputs.

Kinda like pouring water outa a bucket, if u fill and dump a bucket repeatedly; ull see at times there is no water flowing across the ground (like when ur filling the bucket before u dump it again lol, this would be the equivalent of no flywheel at all) but if you were to put another bucket on the ground and dump ur bucket into that one (now we have a flywheel), as the bucket stationary on the ground began to fill and overflow... you would notice there is still flow out of the bucket on the ground, even when the bucket being dumped over and over again is not always dumping water into it...

The point is i believe reducing flywheel weight is similiar to just using a smaller stationary bucket on the ground (now we have a smaller flywheel)... which is wat leads to faster response

So yea u gain faster throttle....
But the downside would be less THUMP when u pop the clutch at the same RPM's for a trimmed flywheel vs. a non-lightened flywheel...

and there is ur physics for the day lol, enjoy ;-)

 

You may want to reconsider if you FI, unless you can remap your idle speed to higher. If you take significant material off, the engine will have to idle faster.
If the flywheel was not installed concentrically, just making the outside round does not necessarily balance the thing, it may make it less unbalanced. Round & balanced are two different things. If the outside is not concentric, the inside isn't either.

 

I've lightened flywheels for many FI street bikes as well, and it had NO effect on the idle at all. And yes, a less skilled person can install a flywheel incorrerctly and throw the balance off....but remember this...the flywheel is on a tapered shaft end and it also has a key way. Kind of hard to mess up the install, but certainly not impossible.

 

why would the mass of the flywheel determine idle speed... that doesn't make sense to me really... once u get the speed in it, its not like its more or less efficient; its just stored energy

 

Well said.