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My mower is a 21" 3 in 1 rear wheel drive. It's a 175cc 7.75 briggs and stratton engine. I've already used it twice this season. I raised the mow height and when I tried to start it there was resistance. When pulling the start cord it comes all the way out and rewinds hard/fast. The first time it bucked and i ended up taking the handle in the chest. It felt like it was trying to start but just didn't catch. I started to tilt it to the side to see if something was binding it and heard the bolt/blade hit the concrete.

I put at new bolt, blade belt, and blade on. Torqued it to the recommended lbs/ft and tried to start again. Once again felt like it was trying to start. On the third pull I hear the bolt/blade hit the ground again. Is there something else I can check next?

Someone has to do it said:

My mower is a 21" 3 in 1 rear wheel drive. It's a 175cc 7.75 briggs and stratton engine. I've already used it twice this season. I raised the mow height and when I tried to start it there was resistance. When pulling the start cord it comes all the way out and rewinds hard/fast. The first time it bucked and i ended up taking the handle in the chest. It felt like it was trying to start but just didn't catch. I started to tilt it to the side to see if something was binding it and heard the bolt/blade hit the concrete.

I put at new bolt, blade belt, and blade on. Torqued it to the recommended lbs/ft and tried to start again. Once again felt like it was trying to start. On the third pull I hear the bolt/blade hit the ground again. Is there something else I can check next?

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Is there dry grass packed under the deck that keeps the blade from spinning...thus the engine unwinds the bolt?

that sounds very strange...

Take the blade mount off and look inside where the crankshaft goes. See if the key is intact. I have seen this problem occur when the blade mount key is broken loose from the mount.

shiftsuper175607 said:

Is there dry grass packed under the deck that keeps the blade from spinning...thus the engine unwinds the bolt?

that sounds very strange...

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There was some dried dirt/grass at the top of the underside. I removed it before replacing the blade. I'll look tomorrow behind the gold colored piece the bolt goes in. I didn't look behind that.

the engine must be running backwards :laughing:

ILENGINE said:

Take the blade mount off and look inside where the crankshaft goes. See if the key is intact. I have seen this problem occur when the blade mount key is broken loose from the mount.

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So, remove the cover over the blade mount, loosen the belt around it, remove the mount. If broken, replace? Do I also need to check the flywheel? I'm watching a lot of you tube at the moment trying to figure out what I'm getting into.

The blade mount turns clockwise without binding. Occasionally there is a slight groan.

The key in most mounts is cast as part of the blade mount. if for some reason you strike an object it will break the mount. Then when you try to crank the engine and the engine stops, remember the blade acts like a flywheel also, so because of direction of travel will loosen the blade.

ILENGINE said:

The key in most mounts is cast as part of the blade mount. if for some reason you strike an object it will break the mount. Then when you try to crank the engine and the engine stops, remember the blade acts like a flywheel also, so because of direction of travel will loosen the blade.

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I've loosened the belt from around the blade adapter but the adapter doesn't want to slide loose. I don't want to damage the shaft? What can i use to remove it?

A lot of penetrating oil and a puller of some sort. A small amount of heat may not hurt anything either.

Someone has to do it said:

My mower is a 21" 3 in 1 rear wheel drive. It's a 175cc 7.75 briggs and stratton engine. I've already used it twice this season. I raised the mow height and when I tried to start it there was resistance. When pulling the start cord it comes all the way out and rewinds hard/fast. The first time it bucked and i ended up taking the handle in the chest. It felt like it was trying to start but just didn't catch. I started to tilt it to the side to see if something was binding it and heard the bolt/blade hit the concrete.

I put at new bolt, blade belt, and blade on. Torqued it to the recommended lbs/ft and tried to start again. Once again felt like it was trying to start. On the third pull I hear the bolt/blade hit the ground again. Is there something else I can check next?

Click to expand...

I have the same mower with the same problem! mine sheared the flywheel key, when I pull the rope it would kick back ,snatch the rope out of my hand and drop the blade. mine was caused by hitting something with the blade.:frown:

I went thru something similar a couple years ago.

My neighbor helped me torch the original bolt off so I could change the blade & bolt. I got a grade 8 bolt from the local hardware store but it wasn't sufficient. The bolt would not hold and the blade came flying off one day. Took a divot out of my asphalt driveway about 20 inches away from my foot!

I then changed out the blade mounting. It was a single bolt through the blade in to the bottom of the crank shaft. There was a square plate with the edges folded over to keep it from spinning. Pretty lame IMO. I got a solid blade bracket that bolts to the crankshaft, and that uses 2 more bolts to hold the blade to the bracket. Much more secure.

I also learned the blade is part of the mass of the flywheel & crankshaft. Trying to start my engine without the blade got me similar results (punched in the chest, motor going backwards, etc). Don't do that again.

PS, the "Slight Groan" is normal in 4 cycle engines. That's the crankcase pressure relief valve doing its job. As the piston goes up & down, the air behind it (inside the crankcase where the oil is) needs someplace to go and get replenished.