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Broken rocker arm

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Old Apr 3, 2011 | 05:26 PM
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Default Broken rocker arm
hello i accuired a 131 in merch motor about a year ago. I put it in a bike and rode about 500 miles and broke a rocker arm. I installed a new one rode another eighty miles and same thing happend. what am i missing? any help would be great thanks

eric
 
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Old Apr 3, 2011 | 05:38 PM
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What kind of a rocker arm broke? Same brand both times? What is the valve spring pressure? What cam? Were the rocker boxes clearanced for the valve springs?
 
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Old Apr 3, 2011 | 05:50 PM
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Both rocker arms were jims 1045 roller rockers. Boxes are clearanced. Unknown cam and spring pressure. Its on the rear intake. shows no sight of extreme heat. Guessin i need to take it down more to see more.
 
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Old Apr 3, 2011 | 08:02 PM
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Where did it break? I would think you have a bind in the valve train or the valve is hitting the piston thats where I would look. Does it bend the pushrod too? It may not some are very strong
 
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Old Apr 4, 2011 | 07:21 AM
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The rocker arm both broke at the pushrod side. I removed the head last night and found that the intake valve has a crack in the middle of it by the stem. Im thinking its getting hot and sticking causing the rocker to break? next thing, i wonder how hard its going to be to find a valve for this hoss since there not available any longer.
 
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Old Apr 4, 2011 | 10:18 AM
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Check the valve sizes - head, valve stem, etc ... you can probably find a mfr who currently makes one to the same spec ....

How does the valve guide look ...?
 
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Old Apr 4, 2011 | 03:17 PM
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rookie mistake, valve not cracked or broken(carbon buildup looked like a crack till i cleaned it off). Valve seat looks good and moves smothe. i know this motor had some issues before i got it but was told only a broken valve spring. Im wondering if maybe the valve stem is too long and causing the spring to over compress and bind. then when the spring releases it snaps back and breaks the rocker. Is that a logical scenerio?
 
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Old Apr 4, 2011 | 05:52 PM
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more like spring bind than anything else. How much lift is in the cam? If you don't know measure with a dial ind. then install a soft spring on the valve with the head on check the clearence with the piston and valve at max lift + also chenk the springs to make sure they don't bind. (bottom out)
 
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Old Apr 4, 2011 | 06:39 PM
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after lookin at the valve spring, it has been bottomed out, you can see where the springs have been touching each round.
 
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Old Apr 5, 2011 | 05:19 AM
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Sounds like you need to supply the cam specs to a shop that can set your heads up correctly, so you can enjoy the bike, instead of pulling a wrench on it.
Scott
 
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