Lawn mower repair question.

Hi. Yesterday while I was mowing the lawn, my mower engine suddenly stopped. The blade continued to spin until it slowed to a stop. It did not strike any objects. It was working fine up to this point.
When I attempt to start the mower by pulling the string, the blade will spin quietly, but I do not hear the engine try to engage. Additionally, it feels "loose" when I pull the string; previously, I could hear the engine cranking, but not anymore.
I'm not very experienced with lawn mower or small engine repair, but I did some basic troubleshooting by looking at guides on the web. The flywheel key, and the blade adaptor key both seem to be intact. The gas is fresh. Oil was recently filled.
My mower is a Craftsman, model 143.996504 with a 6.5 Eager-1 (Tecumseh) 4-cycle engine (917.377431).
Any ideas?
Thanks.
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remove plug, ground ignition wire well to engine block away from plug area.
put finger gently over plug, pull or get someone to pull cord.
do you feel compression? in and out feeling
sounds like broken valve etc from your description easy to pull.......
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Engines basically don't run for one of two reasons:
1. Fuel 2. Spark
If you pull off the spark plug wire, and hold it near the engine (mayb 1/4"), do you get a spark while cranking the engine?
Remove the spark plug (special wrench/socket needed), is the gap either excessive ( > 0.030"), or bridged with carbon fouling? If either, clean, reset gap, and put the plug back in.
If you are getting fuel, you should be able to smell it. The plug should be wet, if there is no spark.
How about the air filter? If it is the sponge type, it needs to be washed out now and then. If it is the paper kind, they have to be replaced every season or so. Take a good look at it. In a pinch, use a whisk broom to clean off the grass clippings, crud, on the surface of the air filter. Put it back in.
That should give you a good start. Also, the manual that comes with your mower should give basic maintainence tasks that you can do.
When you turn the engine over with the pull cord, you should feel some compression, unless the engine is very worn.
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professorpaul wrote:

THREE reasons:
1) fuel
2) spark
3) compression

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If you pull the cord but don't feel and/or hear the resistance of compression, it is probably trash. You've lost a valve or ring. I would guess that you would not be comfortable taking the motor apart to see what may be holding a valve open.
Feeling for compression at the spark plug hole with the spark plug out is more scientific.
My personal decisions about small engines: No compression - trash can Bent crank - trash can Otherwise they are usually fixable. If you have compression, it is probably the flywheel key. You cannot tell unless you remove the flywheel which requires removing the pull rope mechanism, the shroud, and probably the fuel tank. This give you the opportunity to reset the magneto, slip in a new flywheel key (under $5), and clean out the old dead grass and crud. It would be a great time to give it a fresh pull rope too, before the existing one breaks. ______________________________ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

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snipped-for-privacy@yahoo.com wrote:

I will go with the lost compression. If you are up to it you could pull off the head and see if a valve is broke. I do remember one one rare occasion a valve stuck open. Just took some lubricant to get it moving again.
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Pull the spark plug wire off, and secure it well away from the spark plug.
Leave the plug in.
Tip the mower on its side, and try to turn the blade backwards of the usual direction.
If it spins freely, scrap the mower, and get another one. If it binds and gets hard to turn at one or two places in the revolution, then you have compression. Proceed to look for other problems.
--

Christopher A. Young
You can\'t shout down a troll.
  Click to see the full signature.
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On Sat, 19 Aug 2006 21:57:12 GMT, "Stormin Mormon"

I thought with the plug in, the blade could kick back when released or when it slipped out of one's hand. Not enough to cut off a finger, but enough to hurt, no?
And the engine won't start because the spark plug wire is off and "secured" "well away", if it really is. The first time, it probably will be. The second or third time, one might forget. And I used to hook the wire to the fuel line, which in an old mower was a convenient place, but sometimes it sprang loose and went back to within a quarter inch of the plug, close enough for the engine to run.
And anyone who is pushing the blade backwards might want to push it forwards too, not realizing it would be more likely to start.
One could use a stick to push the blade backwards. God only gave us 10 fingers.

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possible to me that your engine has a connecting rod broken at the crankshaft end. That is based on engine spinning freely without any sounds. The engine is likely beyond economical repair.
There are some other possibilities, such as a valve being stuck open, that are easily repaired. If it spins over easily there can be no compression. I would have someone knowledgeable have a look at it if possible.
Don Young
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Sound advice.

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a broken connecting rod would be memorable noisey event, short but exciting.
sounds more like a stuck valve, thats occured here
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wrote:

Nothing like the sound a "knocking rod", spun rod bearing, or broke valve.

Easily checked at the tappet filter / crank breather (if this model has one) - remove it and pull the cord...the valves should move and easily viewed. The easy way; pull the plug wire and plug, determine which digit goes into the plug hole. Rotated through all four strokes: intake, compression, power, exhaust - you can feel the intake pulling the finger, Compression stroke will blow the finger out.
Oren
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I think I had one once, where the pin holding the spring in place had come out. One spring of the two was fully extended, even more than needed to close the valve. The spring was iirc loose, because nothing held it in place at one end. At the time, I would never spend enough for a valve spring tool, but a shop could have fixed it in a few minutes I guess.
The easy way; pull the plug wire and plug, determine

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Take out the spark plug and shine a flashlight in there while pulling the cord to see if the valves are moving. I've seen those cheap plastic (yes, plastic!) cam gears break in half.

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