Small engine (B&S) question?

[pbm]

I'm not having much luck with my mowers this year. A couple of weeks ago my 18 y/o Murray riding mower finally crapped out. This was to be expected. Tonite my 9 year old B&S 6.5 hp push mower apparently died. I had put on a new mulching blade and I thought the mower wasn't cutting low enough so I lowered the deck 2 notches. This made for a nice tight cut but apparently it 'strained' the motor. (this motor was running like new before I started but it made a strange noise a few times while I was mowing) About 3/4's of the way thru my 3/4 of an acre the blade began to spin freely.
When I flipped the mower up to take a look I found a free spinning blade (no resistance). I assume I've blown the motor. What do you guys think I've broken? Is this worth fixing on an otherwise fine mower? What will this repair cost?

 

[Quest]

Your soft metal key could have been sheared due to hitting something hard or load.

I would pull the blade off, flip the mower back to normal position and then try firing it up and see if the engine runs properly (check your oil level and spark plug condition, and replace them if necessary ((spark plug should still be Champion RCJ8/CJ8 type if memory serves). If engine runs good, you just have to get another key. If your engine runs like crrrapp with lots of vibrations or none at all, you probably need a new engine (maybe sheared crank>?? nobody knows unless you start taking things apart to inspect).


Q.

 

[Bror Jace]

pbm, how does the motor run, independent of how the blade is turning?

Have you pulled the sparkplug, pulled the starting cord and checked for compression?

I'm with Quest, I bet it turns out to be a sheared key, failed brake clutch or some other 'driveline' problem instead of and engine problem.

When you say the blade now turns freely, HOW freely? Even a blown motor (thrown rod, blown piston, etc ... ) will probably prevent the blade from spinning 'freely.'

I hate to ask a stupid question ... but did the bolt holding the blade on loosen up by chance?

 

[olddognewtrks]

Be careful pull starting a single with no blade. The lack of flywheel from no blade made mine a pain (literally) to start (I was doing it for the heck of it when blade sharpening). The kick back yanked the handle from (through) my fingers. OUCH! That's all right, though. I've got more fingers on the other hand.

 

[Brett Miller]

Yes, listen to olddog. I will hurt like $!%#! when it kicks back. Sounds to me like the blade just came loose. If the engine had blown, there would have been some noise or associated fireworks.

 

[yeehaw1960]

Pull the spark plug wire (not the plug). Lift the mower up (muffler side up!)enough to access the blade. Spin the blade. Does the shaft move too? If not, the blade just needs to be reinstalled. If the shaft moves freely (very freely like a fan blade), you're 100% hosed and should proceed to the nearest retail establishment that sells mowers. If the engine was intact, the blade would turn, but wouldn't spin like a pinwheel due to the engine's compression. Please, don't forget to unhook the plug wire!

 

[pbm]

The bolt holding the blade is tight but the blade just spins freely. After taking a closer look I think that if I add another washer the blade would be tight and my problem would be solved. (It was getting a little dark last evening and I really couldn't get a good look at it). Thanks for all the replys. BITOGers are always willing to help each other out.

 

[Quest]

LOL! looks like your replacement blade could be a bad one (e.g. missing some locking holes/slots to prevent the blade from freespinning).

You shall seriously look into the differences between the original one and your replacement one to check and see if there's anything different in terms of blade thickness, etc. When in doubt, always resort to using/buying OE blades.

adding additional washer isn't gonna solve your problem properly if you don't have the blade properly lock down in it's place. It'll spin free again within 5 mins of runtime, guaranteed.

Q.

 

[blupupher]

Hmm, the 2 different blades I have taken off had a large main bolt and 2 smaller side bolts to prevent this. I guess this one has some type of slot or alignment pin?

 

[Steelhead]

make sure that any new replacement blade is well balanced.
test it. don't blindly accept the manuf.

mulching and thatching blades put far higher loads on the engine, both horsepower/torque demands and rotational out of balance uneven load demands from lifting clumps of grass, striking the ground

only run thatching blades on days below 75d F to reduce engine overheating

watch the engine for any signs of overheating

 

[pbm]

Steelhead, Thanks for the heads up. I never even thought of that.