4.6 Bigblock Help

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Ferdinand910

Member
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8
So this spring I decided to tear into my Savage again since it broke last summer. I thought I ate another OWB on the rotostart since it wasnt turning over. It turns out the shaft that the bearing sits on, when turned by hand, it does not move the piston. Sometimes you can rotate the shaft by hand and you will get something like a clunking sound and the piston will then move.
I am still very new to working on these things so I have no idea how or what to do from here. Any help is greatly appreciated since I have little idea how to diagnose this
 
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Some of HPI's engines use a spring/pin in the end of the crankshaft that keys into a channel in a flat disk. The spring pushes the pin down into the recess so it catches and turns the engine over. Then once it's running, the engine spins and the spring/pin slips over it. Could be the pin is worn down, broken in half or the spring is gummed up and not able to push it into the disk so it can catch properly.

You can see the groove here:
s-l300.jpg


The groove/pin/spring kind of acts like a "one way bearing". When the shaft is turned, it runs into the pin and rotates the crank, but when the engine is running, it pushes the pin along the surface of the disk and doesn't catch. There was a starter that just relied on this, the disk/shaft had a flat spot on it and there was a cup with set screw directly on the shaft, like a dog bone cup for the roto starter. I don't know if it was unreliable or caused too much drag, but it's a more simplistic approach vs having an actual OWB in there. However, the ones that do have a OWB also have the spring/pin/slotted disk, which I don't fully understand why. Never had one apart or for any real duration to see how it did.
 

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