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B&S 3HP lawn mower engine kick back like a mule

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sugahpop
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2019/10/23 15:55:55 (permalink)
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B&S 3HP lawn mower engine kick back like a mule

Hi All,


Let me introduce myself; I am Jan and recently I stumbled upon a push lawn mower with a 3HP B&S engine from the 94500 series. Alltough it appears the engine is from somewhere the mid eighties and the mower itself is in a kinda 'used'shape. it ran like a charm.
so I decided to do a little tidy up on the mower.
I am not an experienced petrol head but i am not afraid to do some service on project like this.

I intended to clean the engine and the mower, maybe do some paint work, bust most important : the blade needed to be sharpenend since it was blunt like a brick.

So i tried to remove the blade with my impact wrench and immediatley learnend a very important lesson : "you can not tilt the engine in any direction". so i ended up with a carbutor and airfilter full of engine oil (including black pavement...)

I removed the airfilter pulled the cord and  luckily the engine started, coughing like an old man, spitting out smoke like an old MIG jet.
So i decided to take the carbutor and airfilter apart and clean everything thourougly.
I drainded the oil and succeeded finally in removing the blade to sharpen it.

But when i had put everything back togehter and tried to start the engine, the engine wouldnt start.
Instead  it produced a giant kickback. it felt like almost ripping my arm off. After several pulls the kickback even snapped the pullchord.

Reading about this kickback i checked the flywheel key, and it looks fine, in fact it is perfectly lined. I also read something about the plastic camshaft possible being damaged, but i am wondering if a broken camshaf can cause a backfire.

Don know if it can make a difference: i tried to start the engine without the blade attached.

So has anyone else ever experienced something similar?
 
Thnx for your help in advance
 
 
 
 

7 Replies Related Threads

    AVB
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    Re: B&S 3HP lawn mower engine kick back like a mule 2019/10/23 17:19:10 (permalink)
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    First that engine probably has a lightweight and blade is meant to add weight to the flywheel effect. It probably the source of the kickback.
     
    Actually need the engine model and type number plus the date code to see which camshaft you have as there are several for this model series.
    sugahpop
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    Re: B&S 3HP lawn mower engine kick back like a mule 2019/10/23 17:54:00 (permalink)
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    model 94502
    type 5911-01
    code 83030708
    AVB
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    Re: B&S 3HP lawn mower engine kick back like a mule 2019/10/23 18:37:01 (permalink)
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    This engine does have a lightweight flywheel and an all metal camshaft. Camshaft PN 394800.
    Roy
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    Re: B&S 3HP lawn mower engine kick back like a mule 2019/10/23 18:58:49 (permalink)
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    Did you reinstall the blade and torque the bolt to spec before trying to start it?
    kshansen
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    Re: B&S 3HP lawn mower engine kick back like a mule 2019/10/24 10:19:14 (permalink)
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    Roy
    Did you reinstall the blade and torque the bolt to spec before trying to start it?


    Agree that the blade is an important part of the engine. It is, as others have indicated, the "flywheel" for the engine.
     
    Never recall seeing it in writing but assumed the reason for putting a lightweight flywheel on a rotary mower and then depending on the blade to act as a flywheel was to help protect the crankshaft.
     
    Engine would work just fine with a cast iron flywheel and the weight of the blade, might even run a bit smoother. But when mowing a long and you hit a tree root or something else that causes the engine to stop abruptly all the inertia of the cast iron flywheel will have to be absorbed by the crankshaft. End result wold be either a broken crank or very bent one.
    Roy
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    Re: B&S 3HP lawn mower engine kick back like a mule 2019/10/24 11:31:29 (permalink)
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    It also has to do with changing load conditions, a heavy flywheel equipped engine cannot respond as quickly.  A bbc equipped mower has to really work to get the blade moving and is sluggish when in heavy grass.
    sugahpop
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    Re: B&S 3HP lawn mower engine kick back like a mule 2019/10/26 05:54:35 (permalink)
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    thnx for all your reactions.
    It all sounds very logical to me. I surely will mount the blade back and give it another shot. i will let you know the outcome.
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