Flywheel weight
 

Desided to start a new topic for debate.

My original post:

800gram removed from the flywheel/starterclutch, was done over 2 times, but heres the final product. Still more weight to be removed, but we stopped here.
Hopefully this will remove some of the felling of dragging an achor in a bungy cord behind the bike http://advrider.com/styles/advrider_smilies/lol8.gif
http://www.tenere.dk/forumnew/uploads/987/Flywheel1.JPG
http://www.tenere.dk/forumnew/uploads/987/Flywheel2.JPG
http://www.tenere.dk/forumnew/uploads/987/Flywheel3.JPG[/QUOTE]


Thanks for the input :thumbup1: Hope other will chime in aswell, we could gather some good info, and hopefully some more personal experiences.

Yes, better carbs will help much, much more. I've tried several carbs in the past, even double flatsides. But I have grown to like the stockers, for no special reason. I guess they work fine for me, are easy for me to work on, and everything fits intake-wise. I have several trips each year outside this country, so it doenst hurt when things like that are stock.

I've never felt the difference in cruising ability when riding fx. a TT600 which have a lighter flywheel, and it has no sprage/starter-clutch and associaated sprockets ect ect which also weighs a ton. So quite a few lbs less rotating mass. My wr250r beeing a totally different bike, has the same cruising speed as the Xt, but has next to no flywheel weight. I've ridden it geared down for hours straight on the interstate (well, stopping for gas, but otherwise straight for over 250 miles at 65mph)

I really dont think the flywheel affects the cruising speed much, if any. Its more the change in engine rpms, where you have to spin up/slow down the heavy flywheel that makes a difference. The flywheel on the XT is still superheavy, and heavier than most other bikes, even when reduced of 800g. I remember a friend and I once compared my flywheel to his on a ktm 640 enduro. His felt like the cap of a beerbottle in comparison. :D

I removed 550g the first time, and could barely tell a difference. To this day im still not sure if I could feel a difference. 550g is so little percentage-wise, compared to how big the total rotating mass of the flywheel, crank, counter balancers, rod and piston ect is.

Im not doing this for performance. The first time was just to do it, I paid a friend of a friend a case of beer for the machinework, so just about free.

This time I needed to repair the wire for the neutral swich, so I was inthere anyway, and there was talk about different pullers in another thread and I wanted to show/tell how efficient a good puller is.

A friend offered to put the flywheel in lathe free of charge, so we removed some more weight. So less weight, and as you say, smaller diameter.

Sometimes you do stuff just to do it. This is one of theese times. Couldn't find many other who have done it, so I figured why not =) I enjoy my time in the garage aswell.

Anyway: Which tolerences are "looser" on the Xt, compared to the raptor? Small end, crank and piston seems the same? My guess is the cam ect has the same tolerences aswell. (could only find specs for Xtz660, but theyre the same specs as xt600)

wow
only now starting remember how heavy it is : )
and that heaviness with a clear (from now on) presence of so much unnecessary weight really creates some odd feeling.
also there might be opposite point of view, legit at least on the question level - high mass as an energy storage while engine revs evenly...

there's always pros and cons, my 700 supermono roadracer runs without any flywheel at all, just the shell of the rotor to activate the ign sensor. I wouldnt want the kind of pickup it has on the road.

the more you remove weight the less energy storage and also less damping of the rpm change during the crank rotation = more peak loads on the already fragile xt gear wheels. IMHO of course, it will not increase longevity :)

pretty sure your bike will feel more lively in the lower gears but less happy to thump-thump in 5th.

Thanks for the input. My "fragile" gears are at 180.000km.
I have ridden 90.000km with the flywheel reduced by 550gram.

As I said, the 550 gram was just about impossible to notice on this bike. So an additional 250gr wont do much difference. How much is the rotating mass in totall? 20-some kilos? I've removed a very small percentage for sure.

Just to gain some perspective: On cars they reduce the flywheel by kilos, not grams, same goes for overall rotating mass for trackbikes.

With 550gram removed, it would still be heavier than most. And will continue to idle along in 1st gear, and wheelie away when you crack the throttle. So plenty of bottom end/grunt.


Will gladly update the thread when I get a chance to ride the bike. I even have a friend with the same model so I can let him (beeing unbiased) compare. I'll mare sure to pay specialattention to cruising speed. Although it has never been high with this bike. Something like a Dr650 seems better at keeping up comfortably on the interstate, a Bmw G650gs is even better.

I actually just posted the pics because i figured people would appreciate the good machinework performed by my friend. Just setting the flywheel up in the cnc took some ingenuity because of the conical fitting of the flywheel.

Please continue to add your thoughts :D

What you will really notice is when you are cruising along sedately and hit a small hill. the energy stored in a heavier flywheel will allow you to sail over small hills as if they weren't there. with a light flywheel you will be changing gear more often, making for a "busier " ride.

^^ That is more or less what I was referring to when comparing to my 660 raptor motor . The bigger flywheel helps for the steady rpms over varying surface conditions where the lighter ones get more 'upset" when things try to slow the motor . But with the weight differences between the 2 it's no surprize there is a felt difference . I don't think a person can remove enough weight off the XT anchor to do a whole lot . I had looked at installing the 660 or even the newer 700 flywheel on my xt when the starter gear went out but the taper was bigger so it was a no-go unfortunately .

Starting is another area for the more flywheel mass , while initially getting it spinning is harder , once moving it'll help when the motor is sputtering , but again don't know if enough can be taken off to make much difference.

from this point of view (also mentioned in the beginning), I've got the feeling of the increased importance of the removed weight compared with overall spinning weight...
and from some number, this percentage gets more and more noticeable for the rider.
now I start to think also about another detail - "mechanically" flywheel is much closer to the combustion chamber than some other spinning parts are. so, X grams on the flywheel might be equal to >X grams on some other shaft or gear.

Agreed. Also the diameter of the flywheel is now smaller, that alone means more than the actual weight removed.

yeah, that's definitely one more "weighty" point to consider - distance from the center.
I suppose that final difference should be quite apparent. moreover, "pickup lane" doesn't seem to be more than 20% of the overall width.
so, some guys here will look forward for the interesting update after assembly : )

Rode the bike a couple hundred kilometers. Drives like a freight train, like always.

It feels powerfull, but I've just rode 10 days in Marokko on a small 250, so anything would feel powerfull. I think its about the same, not much gained as expected. If anything, revs build up faster. Id would be nice to have made the 2-step weight reduction in one go, and directly test the bike before/after, instead of this. I could compare to a friends bike, but any difference could be because of carburation, state of the engine, ect ect.

Bike still lugs around nicely, it will still put around on its own in 1st gear. No extra vibrations.

So for sure no downsides (for me) and perhaps a small gain. Not something Id throw hundres of dollars after, but well worth it, just for the fun of it. :D