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Cobra 50cc jr clutch question

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#1
I recently purchased a Cobra JR for my grandson. One of his friends told me that this was a good place for getting help or answering concerns. I made the purchase a few weeks ago, and the gentleman I bought it from said that he would recommend (sorry if I use the wrong verbage) replacing the stack of springs and the clutch milk. I was hoping for 2 things. Most importantly should I be concerned that it needs new parts already and secondly where do I get the parts with some technical assistance?

Thanks and I hope your patient,

Pastor Bob
 

Ol'89r

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#2
Paster Bob. The Cobra Jr, if I remember correctly :coocoo: has an automatic clutch. Different strength springs will determine at what RPM the clutch engages. By 'Milk' I take it you mean oil. Changing the oil is standard maintainance and should be done often. For parts and tech info check out Cobra's web site at cobramotorcycle.com. The owner Sean Hilbert used to be a member here at DRN. Not sure if he is still here.
Good luck. :cool:
 
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#3
Thank you very much, In speaking with some other Cobra owners here in Iowa, they tell me that the spring stack has to be measured. I've been looking all over the internet to find a better way then a micrometer. I've used them before and I just don't know with a flexible part they can give an accurate reading. I really want Wes to have success early so that he sticks with it. Sorry if I'm being too picky.
 
- a d v e r t i s e m e n t -

Ol'89r

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#4
It's not that critical. You can use a pair of dial calipers to measure spring length. A stiffer or longer spring will allow the engine to gain more RPM before the clutch engages. A softer spring will make the clutch engage at a lower RPM. For better starts and better pull out of the corners, go with the stiffer spring. That will allow the engine to get up into the power band before the clutch engages. It's mostly trial-and-error to get the performance you are looking for and what your grandson is comfortable with.
 
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#5
I apologize for not knowing the proper wording. My grandson Wes informs me that what I hold in my hand is a washer stack. Between the washers moving around and trying to use the right pressure to get a good measure I'm flustered. I've turned wrenches on cars, boats and a ton of farm tractors. But I was never worried about a "holeshot" if that's even the correct terminology. Is there any other way to measure the "washer stack" besides my micrometer. Wes thinks I'm too picky but as I understand the more unified the measurement the better the take off?
 
- a d v e r t i s e m e n t -

Ol'89r

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#6
pastor_bob said:
I apologize for not knowing the proper wording.
as I understand the more unified the measurement the better the take off?
Don't worry, by the end of the season you will know all of the right words and even a few you won't be able to use on the pulpit. :whoa: :rotfl:

There again, use a pair of dial calipers. The washer stack is the same as a stiffer spring. The more washers you use the stiffer the spring. The stiffer the spring the higher the RPM BEFORE the clutch engages. You want the engine to be able to rev to a higher RPM before the clutch engages to get a better holeshot. To a point.
 
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#7
I truly appreciate the response, I'm pretty familiar with engines and the mechanics from working on cars. I've posted on other sites and I hope this makes sense. I know there are ways to measure a valve springs installed pressures even before installing and I may be making a leap. But is there a way to measure a washer stacks pressure after it's been installed?
 
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#8
I think I've found my answer

Gentlemen,

I think this is the answer I was looking for.

You don't know if the pressure required to compress the stack is the same for all three sets of washers unless you have the tester they have at the factory. As far as I know Cobra is the only place that tests each stack for compression to get the three stacks perfectly matched so that each shoe engages the basket at the same time and with the same amount of force. All others simply measure the total height of each stack with a caliper and assume they are hitting at the same time if all three of the heights are the same.
 
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#9
AFTER A LONG SEARCH IN THE WILDERNESS I'VE FOUND IT.

Thank you to all of you who have helped me on this pilgrimage. With some help over the weekend of a very patient Cobra Father I found it!

Gentlemen,

This is what I've been talking about. I've ordered one and am so excited to see it in action.

http://www.youtube.com/watch?v=WrMSMk82sO4&feature=g-upl
 
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#10
I just want to thank you all again. With the help of Wes's father we ordered the tool yesterday. I hope to have it Tuesday. I know it seems like a small thing but thank you all.
 
- a d v e r t i s e m e n t -

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#11
I felt an obligation to all of you that have been so helpful. I received the clutch setup tool. Being as consistent as I could they each came very close to .554. Or as close as these old eyes could read. I used the tool on the first stack dry and never got the same pressure. It ranged anywhere from 150 to 167. The second stack read 197. The third stack I emery clothed the washers and WD-40'd them and they read a consistent 167 every time. I then repeated the process on the other two stacks so that I had 3 washer stacks with a consistent 167 reading on each shoe. I know this was my own little obsession but with your help and a lot of internet searching I think I've found a tool that could help a lot of people. So I will ask you gentleman a couple of things. 1) Are there any others that have had to same desire for these results as I did? 2) How would I let them know with out being a money changer in the temple. If you understand that reference.

Again

Thanks All!
 

_JOE_

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#12
Glad to hear you found what you needed! I'm sure there's a bunch of obsessive mini dad's out there that would love to have this tooling/knowledge. I know if the day comes to get my boys racing I'll certainly look into anything that could provide a tuning advantage.

On a side note, I think it's awesome that you're helping him do as well as he can. Alot of kids don't have that kind of support. He's a lucky kid for sure!
 

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