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Joined: Apr 2009
Posts: 288
Apprentice level 3
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hi all,
i have a old Tecumseh 4 stroke that keeps shearing blade boss bolts and keys. I have had to replace the bolt that screws into the blade boss twice (not the one into the crankshaft).
i have also had to replace the key on the crankshaft once.
it has very good compression, and starts 1st pull with no real kickback. I don�t know what to do next. Could it be an incorrect coil gap causing it?
Thanks for you ideas,
regards jay
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Joined: Dec 1999
Posts: 5,415 Likes: 36
Repair Junkie
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mowernut, Replace the key in the flywheel as I am sure that it is damaged. 
Regards, ![[Linked Image]](https://www.outdoorking-forum.com.au/forum/images/members/mower-monsterw.jpg) Bruce Please do not PM me asking for support. Post on the forums as it helps all members not just the individual.
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Joined: Apr 2009
Posts: 288
Apprentice level 3
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hi again,
iwent out to the shed this morning, and Bruce you were right the flywheel key was 1/2 sheared. I then reset the coil gap and went and started her up and low and behold I mowed for 1 hour (it was very wet thought) and she held together. I recon at high speeds the coil must have been creating resistance, and shearing the bolts and keys. So keep it in mind next time, it may be an incorrect coil gap!
Thanks for the help
Regards jay
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Joined: Dec 1999
Posts: 5,415 Likes: 36
Repair Junkie
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hi again,
iwent out to the shed this morning, and Bruce you were right the flywheel key was 1/2 sheared. I then reset the coil gap and went and started her up and low and behold I mowed for 1 hour (it was very wet thought) and she held together. I recon at high speeds the coil must have been creating resistance, and shearing the bolts and keys. So keep it in mind next time, it may be an incorrect coil gap!
Thanks for the help
Regards jay Jay you will have three reasons for the key in the flywheel to partly shear one is running the mower without a blade plate and the other is if you have hit something and last but not least if the mower has a bar blade and it could be out of balance. As to the coil gap I have not experience that in the past. The coil gap you can usually use a normal business card to set it.
Regards, Bruce Please do not PM me asking for support. Post on the forums as it helps all members not just the individual.
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Joined: Apr 2009
Posts: 288
Apprentice level 3
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Hi all,
The motor was originally running a small hydraulic pump with a ram thought a v belt set up. I then rescued it from the scrap bin and stuck it on a victa base with a standard blade and boss on it. I then mowed about 2 minutes when it stopped. I found the boss bolt had sheared. I replaced it then mowed for a further 10 minted when this time the key between the boss and crankshaft sheared along with another bolt. I replaced them a week ago, and then the other night thought I would see if anyone else had ever the same bizarre problem. I then re set the coil gap and replaced the flywheel key, and mowed for one hour. I don�t know how the engine was running with a 1/2 sheared key, but after replacing the key and resetting the gap i was able to mow for over a hour in thick wet grass so I assume it was either the coil gap being too close to the flywheel or the 1/2 sheered key causing the boss to shear.
Thanks again for your ongoing help
Regards jay
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