Bolens Lawn Tractor keeps shearing flywheel key

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  #1  
Old 02-26-09, 05:32 PM
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Question Bolens Lawn Tractor keeps shearing flywheel key

I hope someone can point me in the right direction here.

i Just bought a used Bolens lawn tractor/ riding lawn mower
used that had been sitting for a few years. i drained the old gas rebuilt the carb and did a valve adjustment, and cleaned up the spark plug.

basically i followed the advice from 30yeartech on another thread about a bolens not starting and finally discovered the shear key was sheared. i have since sheared 2 more aluminum keys just trying to start it and one steel one that allowed it to run for 30 seconds before i shut it off it backfired and sheared the steel key.

if i take the spark plug out the motor turns with little effort and is a lot harder to turn with the spark plug in.

the valves are moving smoothly with no binding, there does'nt appear to be any binding from the bottom pully that activates the blades. i cant "see" any movement in the crankshaft that would lead me to belive that the crank is bent.

and im fresh out if ideas, anyone? anyone? please?...... help!
thanks in advance!
 
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  #2  
Old 02-26-09, 06:30 PM
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First I would isolate the problem to the engine by pulling off the accessory belt/belts and see how the engine does by itself.

If it starts OK, let it run for about fifteen minutes, getting the carburetor set to accommodate all rpm ranges.

Then hook everything back up and see where you're at.

What engine do you have on the mower?
 
  #3  
Old 02-26-09, 06:37 PM
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the only thing attached to the bottom of the crank is a pully nodrag from a belt or anything any else would that still affect the overall isolation?

Cheers!Beer 4U2
 
  #4  
Old 02-26-09, 06:40 PM
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i forgot the engine is a briggs and stratton model 31c707
type 0154e1 code 0303122c
Beer 4U2
cheers!
the bolens numers are 13an683g163
 
  #5  
Old 02-26-09, 09:12 PM
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It's one of two things causing your problem. Either you have grease or oil or something on the crankshaft, and/or you aren't tightening the flywheel nut tight enough. The key should not hold the flywheel in place. It is only there to get it timed correctly, but it should shear easily if something happens to cause such a reaction. The friction of the tapered shaft against the inside of the flywheel when the bolt is tightened is all that should hold the flywheel in place...so there's no need for a steel flywheel key. A plastic one would even work. Make sure the crankshaft and inner bore of the flywheel are clean, free of oil and grease, and dry before assembly. Tighten the bolt very tight, then tighten it a little more.
 
  #6  
Old 02-27-09, 05:41 AM
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As Cheese mentioned. Are you torquing the flywheel nut to 100-foot pounds? A flywheel not correctly tightened can result in sheared flywheel keys.

Why is the engine backfiring such to shear the key? Backfiring (lean backfire) is attributed to carburetor problems more than anything else. Clean the carburetor more thoroughly. If the carburetor is a Walbro did you remove the nozzle (emulsion tube) and clean it well? Ensure every passage is clean.

Another thing that can cause is an exhaust valve leaking during operation. A leakdown test with the engine hot will detect whether it is leaking.

What compression should my engine be reading?

Building and Using a Cylinder Leakdown Tester

What are the procedures to follow when overhauling the carburetor?
 
  #7  
Old 02-27-09, 10:21 AM
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thanks guys! gonna make a new shear key and tighten the heck out of it and see what happens! the back fire was at low idle when shutting off the engine. the carb is a walbro and it was covered in tarnish now its sparkling clean i followed the mtd instruction to the T, but it wont hurt to do it again. ill let you know what happens. thanks very much again!!!


Cheers!
 
  #8  
Old 02-27-09, 11:33 AM
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I suggest you purchase a key. A local dealer should have them.
 
  #9  
Old 02-27-09, 11:46 AM
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Airman, all of my local shops are out so i made one out a peice of stock. im going to buy a few on my way to work out of town today and replace it.

first the good news, i torqued it down like you guys said and it worked like a charm. motor fired right up and sounded good for about 4-5 seconds. then it died very slowly almost like fuel starvation or vapor lock.

tried to crank it over again and wouldnt crank over very far so i pulled the plug and valve cover to check everything out and the bottom valve had loosened up so i went throught the valve adjustment per mtds site put the plug back in and turns over great but wont start and is producing a fair amount of fuel mist back up thru the intake.

im thinking the carb is still not clean enough or maybe just bad? the solinoid on the bottom of the carb bowl works fine per the MTD site test. the cost of the rebuild kit is $30 and a whole new carb is $80 wonder if i should just buy a whole new carb or go thru it again?

again thanks very much for you patience and help!!!!!

cheers!
 
  #10  
Old 02-27-09, 05:14 PM
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Blowing mist out the intake sounds like the intake valve is too tight. How much compression does the engine have?
 
  #11  
Old 02-27-09, 11:31 PM
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you know cheese that sounds right having spent all night at work thinking about it i think the valves are not adjusted properly. i cant tell you for sure how much compression my tester broke but its hard as heck to turn over by hand with the plug in. but it would make perfect sense, after the one rocker coming loose i bet i over tightened it like over compensating. well time to get back on mtds site and do it over again! yay me! lol thanks ill let you know what happens!!!

Cheers!
 
  #12  
Old 02-28-09, 07:27 PM
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success! after RE-reading the instructions from MTD and following them correctly it runs like a champ! thank you guys very much for your help! next mission is making sure the blade deck and all are in proper working order.

so far this bolens has cost me $ 200.00 for it it self $47.00 for a new battery $5.75 for a few flywheel keys and a few days. so far im thinking i got a deal considering its only three years old!

if anyone knows of a link for the deck adjustment and maintence i would appreciated it.

again thank you very very much!!!!!
Slainte!!!!! (CHEERS)
Beer 4U2
 
  #13  
Old 03-01-09, 10:18 PM
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well, everything worked great for about five minutes then it stalled and wont restart. i have narrowed the problem down to the carb, if i put starting fluid in it it starts right up.
im thinking that because i didnt flush the fuel tank some debris got down thru the filter (not the best stock) and clogged a jet or one of the tiny openings. tommorow after work ill tear it apart again and see what happens next!

cheers!
 
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