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Old 04-20-2014, 07:43 AM   #1
jar944 OP
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Joined: Aug 2010
Location: Chantilly VA
Oddometer: 613
cr500 gets a rekluse Core EXP

I installed a core exp in my YZ250 I really liked the results and wanted to add one to my cr500 to make it a better "do-all" bike. The biggest problem is that Rekluse doesn't offer a core exp for the 500. They Do however offer one for the Cr250 and Crf450. The good thing about that is the 250/450/500 share the same clutch plates and have the same transmission primary shaft dimensions. With that being the case I called up rekluse and bought some of the parts for this project just over a year ago


The biggest hurdle (or so i thought) was the lack of a available (deeper) clutch cover from rekluse that would fit the 500. I knew I needed to fabricate one for the project to actually move forward. Unfortunately making oe took a back seat to a bunch of other things and the project just sat collecting dust.

Fortunately that gave me time to become familiar with the principals behind its operation and better understand the requirements for it to work on a 500.

measurements from the exp "ring":

Total wedge weight 159g (factory heavy wedges)
wedge spacing diameter (centers) min 124mm, max 131mm
ramp angle 18.5 deg
opposition spring force (not measured)

engine parameters
primary reduction 2.52:1
idle RPM 1500 rpm



Fc = m v2/r
= m (n 2 ? r / 60)2/r
= 0.01097 m r n2

where
n = revolution per minute
Or in this case

.01097*m*r*(n*n)
m = .0159kg
r = .062m
rpm = 595

.01097*.0159*.062*(595*595) = 38.3N

Which lead me to wonder how one would calculate how much torque a clutch could theoretically hold (hello unform wear theory)



once I had that I was able to put together a spreadsheet to play around with the clutch parameters



With that done I came to the conclusion that the factory "heavy" wedges were going to slip to much at low RPM. I needed more weight in the wedges but being somewhat limited on space the only viable method in adding mass was to use a more dense material. I had wanted to use a machinable tungsten but its expensive and i'm cheap. The next best option I could think of was using bronze or brass and making them slightly larger.

I picked up a brass "drop" from ebay for $7 and started machining









Once they were finished I weighed them and plugged the numbers into my spreadsheet.

Custom wedges vs factory "heavy" wedges


With that done i still needed to make the clutch cover. So i ordered a chunk of aluminum and got started.













Once the cover was done I installed the clutch with the factory wedges and took it around my yard. as I expected it seemed like it could be more aggressive with the engagement.

However being a tiny yard it was impossible to really evaluate so I left them in for the first test ride. (I was also worried the opposition springs were to weak for wedges 2x the factory weight.) I loaded up the bike and went to my local riding area. I took it out on a 16 mile rock loop I quickly noticed it was slipping a lot on the bottom and made it feel like a 250 (and made you ride it like a 250) the setup was way to revvy to for my liking.

After i got back to the parking area I swapped in my custom extra heavy wedges.


I was still very concerned the custom weights were going to overpower the springs. The worry disappeared as soon as I clicked into 1st and let out the clutch. It was a bit grabby at idle but the core is supposed to be. a quick function check every thing seemed good and then out into some more rocks. SUCCESS!! it grabbed when it was supposed to. You could ride a gear or two high without slipping. It felt like a proper 500... only it was impossible to stall.

jar944 screwed with this post 04-20-2014 at 08:35 AM
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