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-   -   cr500 gets a rekluse Core EXP (

jar944 04-20-2014 07:43 AM

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

F<sub>c</sub> = m v<sup>2</sup>/r
= m (n 2 ? r / 60)<sup>2</sup>/r
= 0.01097 m r n<sup>2</sup>

n = revolution per minute
Or in this case

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. :clap

anonny 04-20-2014 01:12 PM

Nice work, I assume this is for the engine that was stuffed into the KTM frame?

jar944 04-20-2014 01:40 PM


Originally Posted by anonny (Post 23980251)
Nice work, I assume this is for the engine that was stuffed into the KTM frame?

You assumed correctly

sailah 04-20-2014 02:10 PM

That. That is awesome.

I'll admit my eyes glazed over the math and I went right to the machining pics:D

Pezz_gs 04-21-2014 12:44 AM

Brilliant work there!! :freaky

So are you going to offer the wedges in kit form :evil

I have a line on a CR500 engine and would love a Rekluse as I have one for my DRZ400 (462cc)

jar944 04-21-2014 08:41 AM


Originally Posted by Pezz_gs (Post 23983879)
Brilliant work there!! :freaky

So are you going to offer the wedges in kit form :evil

I have a line on a CR500 engine and would love a Rekluse as I have one for my DRZ400 (462cc)

Setting aside possible patent issues, I dont have enough time to get my own stuff done.

Rekluse actually makes a auto clutch for the 500, but its the pro not the exp based core. Im just not a fan of th resulting lever feel or variable engagement point on those.

davesupreme 04-26-2014 04:43 PM

very nice work!... :eek1

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