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 18Hp Briggs & Stratton issues

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1969PowerKing
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PostSubject: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeWed Dec 21, 2011 11:02 pm

Well I have a 1993 Craftsman Lawn tractor, with straight pipes coming out of the motor and exiting out the back. I put a new battery in the tractor, complete new wiring , and got the starter rebuilt, now it turns over great. but when i went to start it up i heard a loud Pop noise coming from the exhaust. So i checked if the rods were thrown, not i was getting spark and then while cranking the key i checked the exhaust, it was shooting smoke out of each pipe. And when i turn it over using the key, it sounds like it trys to start, but nothing, i thought it could be somthing with the vavles, considering i have already rebuilt the rest of the motor. So it any body knows whats the problemm please let me know thanks.
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dangeroustoys56
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PostSubject: Re: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeFri Dec 23, 2011 7:11 am

Only way to tell if its the valves is pull the heads - could be a bad magneto - also might want to check the flywheel key and make sure it hasnt spun the flywheel off timing.
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1969PowerKing
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PostSubject: Re: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeFri Dec 23, 2011 11:35 pm

well right now im not able to work on it (vaction) But what if i checked the valve covers to see if a spring might be bad, low back pressure, striaght pipes
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PostSubject: Re: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeSat Dec 24, 2011 12:01 am

If you were getting spark but it's backfiring that's a good indication of a bad flywheel key, as dangeroustoys said. Pulling the breather covers will allow you to check tappet clearances, but that's about it. I'd do a compression & leak-down test to identify any possible compression loss. Are you sure there's no issue with carb or fuel pump?
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1969PowerKing
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PostSubject: Re: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeSun Dec 25, 2011 10:32 pm

Well i rebuilt the fuel pump about 3 months ago, what exactly is the fly wheel key, like the key way where the crankshaft matchs with the fly wheel?
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PostSubject: Re: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeWed Dec 28, 2011 1:52 am

its your valves..... either you broke a valve off or keeper came out... mine was making a loud pop/backfire sound and blowing puffs of smoke occasionaly but never starting.
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dangeroustoys56
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PostSubject: Re: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeWed Dec 28, 2011 7:43 am

Flywheel key is a small piece of metal that keeps the flywheel and crank timed together - if the crank end ( underneath encounters something- the flywheel key is designed to shear to prevent damage to the motor.
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1969PowerKing
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PostSubject: Re: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeSat Dec 31, 2011 7:13 pm

I decided to start by checking the fly wheel key first, for less issues hopefully. got the 1 1/4" nut of the crankshaft, and relized the key way was sheared, i was like thank God!Very Happy Because i replaced the head gaskets this past summer. so i didnt what to do that. But i went to napa, got a new key way, put it in, and put the nut on, hand tighted. and it did the same thing, sheared it. And then i realized what had happened, the key just keeps it on the right settings, and the nut aucaly hold it in there, so i put the impact on it and tighted it up, and it works. Thanks for every ones input.
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PostSubject: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeSat Dec 31, 2011 7:24 pm

yep, gotta get the nut tight. the key is used for indexing the flywheel for timing, but is also used for shear pin. if the motor stops quick (like a push mower hitting a water meter) the key will break instead of twisting the crank.
Dont over torque the nut though. I have seen stripped threads on the crank from using a big impact. the motor is pretty much junk after that, unless you happen to have a spare crank laying around
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dangeroustoys56
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PostSubject: Re: 18Hp Briggs & Stratton issues   18Hp Briggs & Stratton issues Icon_minitimeMon Jan 02, 2012 3:26 am

Yeah, the flywheel is a 'press fit' onto the crank - why the crank and flywheel have a matching taper.

Ive gotten motors with snapped flywheel keys , one i bot at a tractor junkyard, a OHV 14.5 briggs - they 'supposedly' opened it to check it out , well it didnt run at all- kept snapping flywheel keys - they said it was because of a hydro lock ( oil in cylender) but that was BS, knew it had something to do with the valves - i had it sitting upright the whole time- they ended up fixing it for free.
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