Briggs 5hp recoil kickback

[petelg]

Hi. I've been tinkering with an older Briggs engine. 5hp model 130202..When I pull the rope the compression and re oil is fine.when I place my hand over the carb breather and pull the rope it will kickback and pop..Nope I can't Bragg about being a good mechanic but I like tinkering with them..So in lamen terms....Please HELP!!...lol..Thank you

 

[ILENGINE]

lets start by making sure the flywheel key isn't sheared or offset. both will change timing and cause kickback.

 

[petelg]

Hi thanks for the help. flywheel seems to be in order...

 

[ILENGINE]

This may be off the wall, but is there a chance that somebody put the lightweight aluminum flywheel on the engine is there. Wrong flywheel would also cause kickback.

 

[Maxrevs]

Hi thanks for the help. flywheel seems to be in order...

Just to clarify, when you say "flywheel seems to be in order" do you mean you've actually unbolted it and used an extractor to pull it off the crank so you can check the condition of the key?

In case you're unfamiliar, once you've got the flywheel off you should find a small rectangular "chip" of metal (approx 1/4") called a flywheel key (sometimes called a Woodruff key). It fits into corresponding grooves in the crankshaft and flywheel which hold the flywheel in position on the crank to stop it from twisting around and throwing out the ignition timing.

This key is what's called sacrificial (there's a similar one underneath the engine which holds the blade adapter in position on the output shaft), they are designed to give way under sudden-stop conditions to prevent damage to the engine, e.g. if the blades hit a tree stump.

If your mower has suffered a sudden-stop at anytime, the flywheel key could be broken or bent. This would have the effect of altering the ignition timing which could be causing the kick-back you describe.

Hope this helps.

 

[petelg]

Just to clarify, when you say "flywheel seems to be in order" do you mean you've actually unbolted it and used an extractor to pull it off the crank so you can check the condition of the key?

In case you're unfamiliar, once you've got the flywheel off you should find a small rectangular "chip" of metal (approx 1/4") called a flywheel key (sometimes called a Woodruff key). It fits into corresponding grooves in the crankshaft and flywheel which hold the flywheel in position on the crank to stop it from twisting around and throwing out the ignition timing.

This key is what's called sacrificial (there's a similar one underneath the engine which holds the blade adapter in position on the output shaft), they are designed to give way under sudden-stop conditions to prevent damage to the engine, e.g. if the blades hit a tree stump.

If your mower has suffered a sudden-stop at anytime, the flywheel key could be broken or bent. This would have the effect of altering the ignition timing which could be causing the kick-back you describe.

Hope this helps.

Hi. Thanks for the help. I have to apologize. I too quickly assumed that the flywheel key was I good shape I took the flywheel back off....And yes the flywheel key was sheered. But was the sheered key the problem for the kickbacks( which indecently felt like my arm would be pulled off...lol) or did a different problem cause the key to sheer?...I'll try to purchase another sheer pen tomorrow.. Again..Thanks

 

[ILENGINE]

sheared keys are rare on horizontal engines sudden stops due to striking an object killing the engine or improperly torqued flywheel or oil residue on the crankshaft taper will also cause shearing

when the engine gets stopped suddenly the flywheel keeps trying to turn which because of the direction of rotation advances the timing hence kickback

 

[petelg]

I replaced the sheer pin in the flywheel...can't get the engine fire again..I'm sure I'm not getting any spark...I WAS getting a least a little juice because I held the plug wire and felt a little tingle.But now nothing..Pete