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fishnwiz

Stuck 8 hp Briggs engine

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fishnwiz

Ok, This is the story. I have been messing with the Jacobsen with the 8hp briggs motor. Engine was free and spun well. I just cleaned contacts on starter and set points and checked spark which was good. I turned the engine over for about 60 secson and off and engine froze tight!I checked to be sure starter was not jammed in ring gear.. I pulled shroud and tried to spin flywheel by hand...NO GO! Pulled head and found NO head gasket and untorqued head bolts like head had been recently removed. Piston seems to be BDC. What would you guess...broken or bent rod? Engine never ran but did have clean oil.. I never did have a chance to check compression.

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dentwizz

Sounds like your bottom connecting rod journal was dry. If you are lucky you might be able to get the bottom cap loosened if you don't rotate the shaft too hard before hand. Do so by opening the crankcase and loosening said bolts. Once open, sand the crankshaft with emery cloth to get the aluminum residue off and allow it to spin again. Be sure to use a good oil like lucas oil additive or gear oil to pre lubricate it when you go to reassemble it.

Usually when that happens it is exactly how you said. Engine that sat long enough for the oil to separate off the surfaces, then run long enough to rub together and get too hot and fuses to the crank. Unfortunately it usually results in a broken rod by the virtue of heavy flywheels but yours is a smaller one so it may be recoverable. When possible if an engine has been in storage or idle for a very extended/indefinable period of time it can be a gamble unless you can pre-oil it directly at the rod since these engines are splash oiled.

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dentwizz

I've had it happen in less than 30 sec on some of the older ones. If the clearances are particularly tight(which would normally be a good thing), dryness can make it hot almost immediately.

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dentwizz

Early on in my tractor hobby I wasted a 10hp Briggs horizontal that I drove 4 hours each way to get to replace an engine on a trac that mice nested and made overheat for the previous owner. Brought it home, added oil and fired it up for 30 sec. Ran like a watch until it stopped cold and blew the rod before I knew which way was up!

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timflury

That photo looks familiar to me Bob. Where and when was that taken?

I toured the Allis Chalmers plant back in the late 70's when they were building ship engines in the plant off of 70th street. A 9 cylinder engine would have a top speed of 128 rpm.

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fishnwiz

That is incredible that the rod bent that far without breaking!

That is some thick steel on the connecting rod.

I don't know what is up with this motor....today it became free again.There is some scratches in the cylinder walls.I did drain the oil and it was clean. I cranked the engine over several minutes without any issues at all..Unknown issues exist.

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BLT
quote:Originally posted by BLT

Mark, sometimes the rod is just bent and does not damage crankpin.:DBentRoda.jpg


id="quote">
id="quote">That bent rod came off of a Watsila 14 cyl inline engine, 102,000 BHP @ 102 RPM. I think it came from the MS 'Emma Maersk', an 11,000 container motor ship.

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