Crushed Spark Plug?


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Old 07-27-20, 05:03 PM
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Crushed Spark Plug?

**Twilight Zone Music***

Toro 4-stroke, 18 inch snowthrower. Pull start is locked - pull the spark plug and it's CRUSHED, like the piston slammed into it. (Yes, I checked, it's the correct spark plug.)

Pull the starter cover off and I can spin the fly-wheel a little more than 180 both ways before the engine locks up. And get this, the piston moves freely up-and-down while I move the fly-wheel!

Probably not gonna fix it anyway but I'm wondering what could be causing this? My first thought was a broken connecting rod but I can't see a reason why the piston would come back down if it was that?

Any help or theory is appreciated.

Thanks!
 
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Old 07-27-20, 06:23 PM
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Can you see a mark on the top of the piston?
 
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Old 07-27-20, 08:02 PM
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Remove head and check for debris floating around. Determine what it is and repair accordingly. Could be a screw from the carb, a valve seat, or valve head, possibly a piece of the piston. You won't know until you look.
Time is the cost to find out.

RR
 
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Old 07-28-20, 12:56 AM
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The terms you're looking for are "interference engine" and "valve float".

My guess- valve spring broke, piston bent valve, valve crushed spark plug.
 
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Old 07-28-20, 04:13 AM
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It's obvious the engine was operating when this happened. Did the augers hit something that didn't move?
 
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Old 07-28-20, 06:29 AM
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@Tolyn Ironhand > negative. I'm only looking through the spark plug hole and the piston looks normal, from what I can see.

:dontknow:
 
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Old 07-28-20, 06:33 AM
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Rough Rooster> thank you, sir. I'm just going to have to do that -- although this machine is fairly worthless so any time invested will have to be chalked up to learning purposes.

Thanks for your insight and response.

 
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Old 07-28-20, 06:39 AM
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Hal_S > awesome supposition, sounds totally feasible. Thank you!


 
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Old 07-28-20, 06:45 AM
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beelzebob> that was not reported to me but I ought to find out. Thanks for the suggestion.


 
  #10  
Old 07-28-20, 02:34 PM
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Yep, OHV valve related.

Pulled off the OHV cover and right away noticed the valve spring just laying there. The valve was nowhere to be found, so the whole thing is probably down in the cylinder, busted apart. The rocker arm was broken and pieces of it were laying out, also the push-rod was laying askew.

Not sure what the nexus was? What happened first? There's no fixing this as the parts diagram doesn't even list the parts as being available. They're just greyed out (see below).

Thanks to all for your insight, I really appreciate it!











 
  #11  
Old 07-28-20, 03:57 PM
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Looks like a an oiling + wear failure. The hole in the "lifter" eh, washer is WAY to round to be a sudden failure.

M guess is a clogged oil channel, so the "lifter" wasn't getting the required amount of oil,
It wore away at the washer over years, until the washer was so thin that the push rod, literally pushed throuh.
Then valve meets piston, and rocker arm breaks.

Which means as you continue the autopsy, the valve should be laying on the piston, and the cylinder should be scraped, scarred and beat to hell from the couple of seconds after the failure when the valve was bouncing around inside the cylinder head.

If the cylinder walls are not horribly scratched, you MIGHT be able to swap in a new rocker/head and get this running.
However, any engine that eats a valve WILL devour oil.

In some cases involving cars 440 "LongHorn" or 426 Hemi, owners are fine with adding 1 quart of oil each time. For a snow blower, not sure it's worth it.
 
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Old 07-28-20, 06:38 PM
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Good call, Hal_S - the oil smells like gasoline so during storage, the float probably stuck and let a sh*t-ton of gas flow into the crankcase thereby reducing the oil's lubricating properties and causing the failure exactly as you cited.

You guys are good!


 
 

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