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Lightened Primary

39K views 56 replies 26 participants last post by  crakerjac 
#1 ·
Has anyone on here installed the lightened primary from mnnthbx? I just orders one yesterday and was looking for some feedback on it.
 
#6 ·
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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#18 ·
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.
 
#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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#21 ·
Now that I've been running this for a while I can say that it's a great mod! The revs pick up faster and drop slower going up steep inclines. It performs great on track as well as commuting. If you have the proper tools this install is super easy and it's probably the best bang for the buck mod you can get.

Also, the MTake from MNNTHBX is a highly recommended mod to go along with it. Knocked both of these mods out in about 20-30 mins and well worth the money!
 
#28 ·
You need to remove (2) 19 mm nuts on the crankshaft & input shaft(needs a deep thin wall socket), then pull the assembled clutch basket and old gear out at the same time. Then 40 lb/ft when torquing the nuts(and some Loctite, too) back on. Easy job if you are familiar with MC wet clutches. Good improvement in throttle response for the money / effort.
 
#29 ·
Super easy swap. Just torque everything back and use blue loctite. I pulled the rear set off for easy access to the clutch cover bolts.

Clutch pressure plate = 7lbs
Clutch hub and primary = 40lbs as stated above
Clutch cover bolts = 7lbs

I had to use an impact to remover the nuts on the clutch and primary and used a clutch holder tool to torque the hub back down. I (carefully) used a screw drive to jam the gears when torquing the primary.
 
#32 ·
yeah i believe it does call for 53 but i have seen videos and posts in places that a few people have broken the clutch back plate at that setting. when i did my hd clutch i only went to about 48 ft/lb. only gone about 60 miles on it so far but no problems yet.

i just ordered the lightened primary myself. when i put it on i will probably use the same torque again.
 
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