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Briggs & Stratton 10HP

New Englander

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With the vast knowledge here I figured I'd ask before I tore it apart.

It's a 10 HP horizontal shaft L head single on a generator. It was sitting running fine and stopped. It started back up right away but is shaking badly. Ignition is strong and since it starts so easily I doubt it sheared the flywheel key, common on lawn mowers when they strike something.  Carburetor looks fine, nothing clogged, needle works as it should. Cranking compression is 90 psi. I suspect it probably has a centrifugal compression release on the cam. 

The shaking is so severe on the rubber mounts that gas is shaken out of the float bowl vent. With the air filter in place that gas gets sucked back in causing it to be rich, which made me suspect a sunken float, but it's OK.

I don't know how it couples to the generator but I'm wondering if something failed there causing a great out of balance condition.

Any ideas? I'll pull it tomorrow and separate it from the generator tomorrow.

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Is it possible to have a coincidence here, like rotten rubber mounts that failed when you restarted? Or if the through- bolt holding the rotor to the crankshaft is loose or broken, the rotor can orbit and cause vibration. 

  Briggs didn’t publish compression figures because of the the compression release, their philosophy is if the flywheel bounces back when spun backwards ( no compression release operation) the compression is at least good enough to start the engine, whether it be mechanical or the early Easy-Spin. 90 is good through the compression release, I think the trouble is somewhere other than the motor.


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2 hours ago, int 504 said:

The rotor usually is on a tapered end of crankshaft retained by a bolt or a nut.

IIRC there is an SAE spec on those.

Does it have a balance shaft?  I had some fun and games with a 16 hp one in that area but its problem was incorrect assembly

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1 hour ago, vtfireman85 said:

Check the generator end bearing i have seen those fail and they are usually pressed into a plastic end cap. 

been there done this, ruined the gen - cheap design and it will break at some point 

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