# Briggs 12.5 hp I/C Syncro, No compression, but...



## luckyvision (May 24, 2007)

Briggs 12.5 Synro I/C engine on a MTD Ranch King (older mower)
Engine:
Model # 286707
Type: 0420-01
code# 9308034E

customer says it was running & something went *SNAP*, then it wouldn't start.

it's got spark, & fuel, the flywheel turns the crank (the pully on the bottom turns)

*-It has no compression*
*-It had barely any oil in it (the droplet on the end of the dipstick was more like Gulf Crude)*

what drives me nuts is that you can only see the intake valve (which moves) thru the spark plug hole, not if the piston moves...

the intake valve does look 'wet' not cooked as if it were overheated. i know the exhaust would cook first, but if the cyl got hot i'd expect the intake valve to at least be ...dry...

i do feel a slight air pluse at the oil filler tube, so i suspect the piston is moving..

so my questions: (finally huh?, lol)

i haven't pulled the flywheel yet, how likely is it that the key sheared, but the crank is still turning? if that was it, wouldn't it still have compression?

if the key is ok, then the only other thing i can think to do is a leak down test.. without being able to see the piston, how do i know when it's on compression stroke? align the coil with the magnet?

just thought of other other thing: does thishave a compression release counterweight on the inside of the cam? maybe it's still stuck open (but then i think it'd at least fire a bit...)

any reason for me to pull the head? can i readily get a head gasket?

Thanks, gentlemen!

--Lucky


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## justin3 (Apr 10, 2007)

With your engine you should just be able to look through the spark plug hole to see if the piston is moving, you may have to remove the hood. It all sounds like a thrown connecting rod considering the snapping sound and the lack of oil. I would pull the head and inspect.


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## luckyvision (May 24, 2007)

*update*

turns out to be a stuck exhaust valve...

Pulled the flywheel, key was good, pulled the head, e-valve stuck open. a tap with the plastic mallot poped it back in. shot some PBlaster past it & gave it a few revolutions by hand & it opens & closes smoothly.

don't know if it's bent (doesn't seem to be) if the guide or seal is any good, but the guy doesn't want to spend a ton of $ on it, so i'm just going to put the head back on, same gasket (came off well in one piece) torque it down (45 ft lbs sound about right) & see what happens, i'll let you know.

Oh, & on this engine, you CANNOT see the piston thru the spark plug hole... that would have been a pretty hard thing for me to mistake, don't you think? That would be like mistaking a carport for an airplane hanger....

--Lucky


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