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Discussion Starter #1
Has anyone on here installed the lightened primary from mnnthbx? I just orders one yesterday and was looking for some feedback on it.
 

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Amazing mod and well worth it.

A lot more acceleration in the low end. I could put 3-4 bike lengths right off the bat on my buddies z when he didn't have one where as before we were neck and neck.
 

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I'll be posting up some numbers once I've got this installed to see just how much of a difference it makes. I've got an AIM lap timer for the track that allows me to do performance tests so I'll be using that.
 

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Everyone who has installed the lighter (unweighted) primary gear says how great it is. But, if there are no downsides to a lighter primary, why did Kawasaki build-in such a heavily weighted crankshaft component to begin with?

This is a single-cylinder engine (and one with a pressed together crankshaft). My bike stalls fairly frequently at red lights. I suspect that if I put in a lighter primary gear, the reduced crankshaft mass would make idle-speed and stalling even more of a problem.

I was just today reading an article by Cycle World's esteemed Kevin Cameron about crankshaft torsion loads. Although a pressed-together crankshaft is obviously cheaper to make than a solid part, it's far, far more complex of an engineering problem to tame. Personally, I'd like to understand Kawasaki's engineering decisions regarding engine design before I make a change like radically lightening my bike's crankshaft mass.
 
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Kawi rightfully used a heavy primary, as the light version requires more revs to pull out initially, and the heavier weight generally makes it easier for beginners. The performance of the light primary is great, and an easy tradeoff for the non-beginner.
 

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Amazing mod and well worth it.

A lot more acceleration in the low end. I could put 3-4 bike lengths right off the bat on my buddies z when he didn't have one where as before we were neck and neck.
where to did buy your lightned primary

i am looking at the one mnnthbx sells and the gojin one steady garage sells
 

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Everyone who has installed the lighter (unweighted) primary gear says how great it is. But, if there are no downsides to a lighter primary, why did Kawasaki build-in such a heavily weighted crankshaft component to begin with?

This is a single-cylinder engine (and one with a pressed together crankshaft). My bike stalls fairly frequently at red lights. I suspect that if I put in a lighter primary gear, the reduced crankshaft mass would make idle-speed and stalling even more of a problem.

I was just today reading an article by Cycle World's esteemed Kevin Cameron about crankshaft torsion loads. Although a pressed-together crankshaft is obviously cheaper to make than a solid part, it's far, far more complex of an engineering problem to tame. Personally, I'd like to understand Kawasaki's engineering decisions regarding engine design before I make a change like radically lightening my bike's crankshaft mass.
Wouldn't the load of the drive train, road, etc be far greater than any inertial load the primary gear would put on the crankshaft?
 

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Everyone who has installed the lighter (unweighted) primary gear says how great it is. But, if there are no downsides to a lighter primary, why did Kawasaki build-in such a heavily weighted crankshaft component to begin with?

This is a single-cylinder engine (and one with a pressed together crankshaft). My bike stalls fairly frequently at red lights. I suspect that if I put in a lighter primary gear, the reduced crankshaft mass would make idle-speed and stalling even more of a problem.

I was just today reading an article by Cycle World's esteemed Kevin Cameron about crankshaft torsion loads. Although a pressed-together crankshaft is obviously cheaper to make than a solid part, it's far, far more complex of an engineering problem to tame. Personally, I'd like to understand Kawasaki's engineering decisions regarding engine design before I make a change like radically lightening my bike's crankshaft mass.
Ive ran this gear on many different KLX110 builds from stock up to 194cc as well as a few Z125's and not a single complaint with stalling. You will lose some engine braking due to less rotating mass but not enough to make the bike stall or case problems in the bottom end. However, once you remove the flywheel weight with an inner rotor kit on the KLX110 (8oz total weight, over 2more lbs weight lose from stock) along with the primary gear, you will **** near lose all engine braking and stalling may come into play. Even then, no problems with durability. Since you can't run the inner rotor kits on the Z.....this should not even be considered a problem with only the primary gear and lightened flywheel. If it is, I would suspect that the problem lies in the engine tune.
 

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I have a lightened primary along with big bore and stroker crank shaft. I thought for sure I would have idle issues, but after the mod I never had an issue with engine not idling after a few seconds of warming up. I did notice you must rev a little more when starting off just like others have mentioned. I also did not notice any real difference in vibration. My two cents.
 

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Discussion Starter #20
Did this a while ago and forgot to post up in here.....


So installed the lightened primary and Mtake from Mnnthbx last night and took it out to put some miles on her before races on Sunday. Tonight was a little cooler then the baseline runs I did last week. Bike has stock exhaust and no fuel management system on it yet.

Bike definitely felt to have more pep. Revs seemed to pick up quicker. Worth the money in my opinion and I like the sound from the intake and I'm sure it would be even better if paired with an exhaust. Install of the Mtake was super easy. Primary gear was a little bit more complicated as you have to have a impact gun to remove the 19mm nut on the gear and on the clutch or a gear holder. Once that's all off getting everything lined back up and on is a little bit of a pain in the *** but. It too bad. I've heard complaints about noise from other lightened primary gears on the Z but it ls barely noticeable IMO.

Here are the 1/8 mile results. Mind you, I'm 215-220 with gear on and this was at 12:30 last night so not the best runs it's capable of....

Before photos are daytime ones and the after are the nighttime pics.

Thanks!
 

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