recently aquired mower having odd vibration issues motor l21zpnc

[lawnboywillneverdie]

i have a motor for a steel deck mounted with no modifications to an awesome aluminum deck found in my local lawnboy parts guys junk area. i know that it isnt the blade as it is fine, but it makes a weird rattle at certain rpms when it slows down but not when going up. it's not too loud but concerns me as i cannot find the source of the noise and i am worried it's coming from the engine. i will post a video of the mower running tomorrow as it is too dark to do it now.:frown: pics will be posted soon. just say what you need a pic or video of so i can get this eluding sound fixed.

 

[gfp55]

i have a motor for a steel deck mounted with no modifications to an awesome aluminum deck found in my local lawnboy parts guys junk area. i know that it isnt the blade as it is fine, but it makes a weird rattle at certain rpms when it slows down but not when going up. it's not too loud but concerns me as i cannot find the source of the noise and i am worried it's coming from the engine. i will post a video of the mower running tomorrow as it is too dark to do it now.:frown: pics will be posted soon. just say what you need a pic or video of so i can get this eluding sound fixed.

If you checked the blade and the blade is not off balance then it has to be some other part that is off balance, what about the flywheel, if a magnet has come off that would throw it off balance. How do you know the blade is fine, tell us how you checked its balance. Is the engine mounting bolts good and tight to the deck?

 

[lawnboywillneverdie]

If you checked the blade and the blade is not off balance then it has to be some other part that is off balance, what about the flywheel, if a magnet has come off that would throw it off balance. How do you know the blade is fine, tell us how you checked its balance. Is the engine mounting bolts good and tight to the deck?

i am posting a video of it running really soon here.:thumbsup:
heres the link Lawn boy start and run - YouTube

 

[jp1961]

I watched and listed to the youtube video. I couldn't pick up the vibration. It sounded pretty good to me. Other than checking all the bolts and nuts for tightness, you could try to see if there is play in the crankshaft after the engine has run and is hot for play (worn bearings). Check when cold too. Another item to check is the flywheel, make sure no fins are broken.

Jeff

 

[Phototone]

It could be a subtle bend in the crankshaft, between the blade and the lower bearing.

 

[jp1961]

Check the blade driver (collar). According the Mechanic's Handbook (page 68), a bent blade driver can cause 'a vibration in the mower and a rough, uneven or ragged cutting may result'.

Jeff

 

[lawnboywillneverdie]

Check the blade driver (collar). According the Mechanic's Handbook (page 68), a bent blade driver can cause 'a vibration in the mower and a rough, uneven or ragged cutting may result'.

Jeff

turns out i was wrong about the blade it has a slight bend in it almost unnoticeable but before filing and hammering down the blade i had done a pass around the yard to compare before and after. almost no smoke during this and it was a cold start too. after that i sharpened and mounted the blade back on and went to go make my second pass. before that i had messed with the mixture and found out that it was running at .75 turns out. runs fine at that. i went to start it and it was smoking moderatly but it wouldn't stop. for about 15min i was mowing and said this cant be normal it has never done this and i stopped. (i had put the mixture screw back at what it was before this jsyk) by then i had smoked up about 2-3 houses in each direction and felt like i gave my mower a bad rep for smoking out the neighborhood. It had never done this before and the gas was fresh and mixed at about 32-30:1. Why would it just randomly start doing this? i cant beleive that it was the muffler just being full of fuel because it would have stopped about 1-2 minutes in. what could this be?:ashamed::smiley_aafz: i will be making a video of it if you guys want me too. btw this is an f series motor. model number L21zpnc but it is mounted to a gold series deck with working 3 speed.

 

[gfp55]

turns out i was wrong about the blade it has a slight bend in it almost unnoticeable but before filing and hammering down the blade i had done a pass around the yard to compare before and after. almost no smoke during this and it was a cold start too. after that i sharpened and mounted the blade back on and went to go make my second pass. before that i had messed with the mixture and found out that it was running at .75 turns out. runs fine at that. i went to start it and it was smoking moderatly but it wouldn't stop. for about 15min i was mowing and said this cant be normal it has never done this and i stopped. (i had put the mixture screw back at what it was before this jsyk) by then i had smoked up about 2-3 houses in each direction and felt like i gave my mower a bad rep for smoking out the neighborhood. It had never done this before and the gas was fresh and mixed at about 32-30:1. Why would it just randomly start doing this? i cant beleive that it was the muffler just being full of fuel because it would have stopped about 1-2 minutes in. what could this be?:ashamed::smiley_aafz: i will be making a video of it if you guys want me too. btw this is an f series motor. model number L21zpnc but it is mounted to a gold series deck with working 3 speed.

Is this engine a 2 cycle or a 4 cycle? Do you mix oil with the gas? If you are mixing oil with the gas (2 cycle) and it smokes then you are using too much oil. If your engine is a (4 cycle) and it smokes then you have bad rings. If you are mixing 2 cycle oil with gas, how are you doing this? Are you mixing it in a 1 gallon gas can? Are you just guessing or are you doing it the correct way and measuring the oil.. When you say "hammering down the blade" You will be getting a new blade after you fix or if you fix you mower, right? After you kinda straightened the blade, did you balance if? A balanced blade is very important to a smooth running engine. If the balance of the blade is off just a little the engine will vibrate.

 

[lawnboywillneverdie]

Is this engine a 2 cycle or a 4 cycle? Do you mix oil with the gas? If you are mixing oil with the gas (2 cycle) and it smokes then you are using too much oil. If your engine is a (4 cycle) and it smokes then you have bad rings. If you are mixing 2 cycle oil with gas, how are you doing this? Are you mixing it in a 1 gallon gas can? Are you just guessing or are you doing it the correct way and measuring the oil.. When you say "hammering down the blade" You will be getting a new blade after you fix or if you fix you mower, right? After you kinda straightened the blade, did you balance if? A balanced blade is very important to a smooth running engine. If the balance of the blade is off just a little the engine will vibrate.

the blade is being replaced next year because it is practically the end of the season where i live. i thought the 32:1 gas oil mix would be a dead giveaway that it is a 2 stroke. the rings are fine and especially for being in a "junkyard" at a mower repair shop nearby me oh and btw they have loads of lawnboys there and they cost $40 for a deck and motor or just 20 for a deck and they have some nice solid state ones too but i have no interest in restoration as i have a lack of funds for the expensive parts needed for a select few of them. I will give you the address of the place if ur interested. next time i go there i will take some pics if anyone that reads this wants me too. P.S. gotta return a motor as part of a deal i made with owner so i will return there soon.) i got my bricktop from there too both of the mowers found are in the exact shape found there and were not rebuilt at all but they run like champs except the one that has started smoking oddly. i may have accidently mixed a little too much oil but doubt that is the prob as it would be almost no difference for i ran my duraforce on it with no problems. i will post a picture of the mower in question.

oh almost forgot can i "mount" a self propel pulley on a non-self propel engine so i can utilize the decent 3 speed that came with my deck? the motor is off of a non-gold series deck that was a push style deck. i mounted it to the gold deck by purchasing a gold series mounting plate and muffler.:anyone:

 

[lawnboywillneverdie]

Here are the pics of my bricktop and the mower that I am discussing. I put one pic in to show the original deck of the f engine an then a couple for its current deck.