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Ignition Timing And The Flywheel Key


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#1 Husky OFFLINE  

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Posted July 30, 2014 - 06:22 PM

I thought I would take a minute to post this. While working on the versa-matic I found that it became extremely difficult to pull start. After a while it just would not start. Upon investigation I found that the spark was weak to none. I figured points or condenser. 

 

I pulled the flywheel and noticed that the key was sheared just a tiny bit. I would not think it would throw the timing off that much but I said hey while I have this apart lets put in a new key and see what happens. I put in a new key and bang, got huge spark and it started on the first pull. So just keep in mind next time a engine becomes hard to start. Here are some pictures of that key. It does not look all that bad.

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#2 LilysDad ONLINE  

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Posted July 30, 2014 - 06:50 PM

Briggs vertical lawn mower engines are famous for this.


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#3 Bolens 1000 ONLINE  

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Posted July 30, 2014 - 07:26 PM

Yep, had this happen numerous times on these B&S engines!


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#4 larrybl ONLINE  

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Posted July 30, 2014 - 07:59 PM

Yep, a key that looks like this, will cause this.

 

https://www.youtube....-tLIZkrLxjJEtbA

 

Replaced the key and (The oil seal blew) Replace it and

 

https://www.youtube....-tLIZkrLxjJEtbA

 

Larrybl

 

 

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#5 superspeedex OFFLINE  

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Posted July 30, 2014 - 08:00 PM

on my horizontal briggs 16hp you can get more power outta them by getting or making a flywheel advance key


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#6 Bill 76 ONLINE  

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Posted July 30, 2014 - 08:23 PM

Briggs vertical lawn mower engines are famous for this.

I wish I had nickle for every key Briggs has sold and a dime for every engine that was tossed because someone thought it was shot when it really only needed a new key.


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#7 lyall ONLINE  

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Posted July 30, 2014 - 08:26 PM

when I have problems with my B&S 5 hp motors, I also check the flywheel key

and that is usually the problem


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#8 LilysDad ONLINE  

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Posted July 30, 2014 - 08:37 PM

Another trick on the Briggs; check the special washer under the flywheel nut. It's a cupped washer and if there are hairline cracks, it may not be cupped anymore. You won't be able to torque the nut down properly and this means it will keep shearing keys.


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#9 Lauber1 ONLINE  

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Posted July 30, 2014 - 08:50 PM

Another trick on the Briggs; check the special washer under the flywheel nut. It's a cupped washer and if there are hairline cracks, it may not be cupped anymore. You won't be able to torque the nut down properly and this means it will keep shearing keys.

that right there is probably the biggest fault people do when they put the flywheel back on, not getting it tight enough to keep the key from sharing off.


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#10 framesteer ONLINE  

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Posted July 30, 2014 - 08:57 PM

Most lower hp Briggs engines use an aluminum key.  It was made from aluminum on purpose and intended to be the "weak link" when the mower struck an object other than grass.  Better to shear the aluminum key than to bend the crankshaft or break the flywheel, or damage the crankshaft.  How easy this key shears on both horizontal shaft and vertical shaft engines depends on the torque on the flywheel nut (or starter clutch).  The torque spec varies by engine model from 55 to 145 ft-lbs.  Check the engine manuals on this site for the proper spec for your model. Bigger engines require more torque. Over-tightening may split the flywheel.


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#11 Bill56 OFFLINE  

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Posted July 30, 2014 - 09:45 PM

I,'ve had this happen too. Bothersome, but a somewhat easy fix. Good part about it... I,'ve gotten many push mowers for next to nothing, because people don't know how easy and inexpensive it is to fix the problem.


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#12 JDBrian OFFLINE  

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Posted July 31, 2014 - 05:39 AM

A small amount of movement in the key will translate in a lot of angular rotation as far as TDC and timing goes. This is a good topic and thanks everyone for posting all the info. on this problem.


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#13 Husky OFFLINE  

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Posted July 31, 2014 - 06:20 AM

Another trick on the Briggs; check the special washer under the flywheel nut. It's a cupped washer and if there are hairline cracks, it may not be cupped anymore. You won't be able to torque the nut down properly and this means it will keep shearing keys.

 

Now that I did not realize, good info thank you.


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#14 TAHOE ONLINE  

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Posted July 31, 2014 - 09:44 AM

I have an LT Snapper rider that recently started back firing with 12 Hp vertical B&S. The PO told me to check the key, that was the same reason why he got it int he first place. Ran fine when we shut it off, back firing bad when we started back up.

I still gotta pull tins to comfirm


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#15 Husky OFFLINE  

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Posted July 31, 2014 - 11:05 AM

I have an LT Snapper rider that recently started back firing with 12 Hp vertical B&S. The PO told me to check the key, that was the same reason why he got it int he first place. Ran fine when we shut it off, back firing bad when we started back up.

I still gotta pull tins to comfirm

 

Well I hope that your issue is the key. It would be nice to know that it helped solve a problem out there.


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