Replacing gear ring on briggs and stratton - HobbyTalk
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post #1 of 19 (permalink) Old 01-07-2009, 03:08 AM Thread Starter
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Replacing gear ring on briggs and stratton

Hi folks, hope one of you can help me out.

My bro-n-law has asked me to fix his murray riding lawn mower. No surprise there, he asks me to fix every time something of his fails.

It is obvious the teeth on the starter gear ring are destroyed. I need to remove the fan/magneto from the crank to replace this gear. My problem is, I can't find a place to grip the crank to break the bolt holding the magneto. I have tried placing a pipe wrench on the shaft that drives the PTO, but that shaft breaks free before the bolt. Two part Q: is the bolt that holds the magneto/fan left handed or right handed threads? and how can I prevent the crank from turning when I apply torque?

Please help, my bro-n-law is a chairman of the decons, or something, of his church. So if I can fix his lawn mower I have a sure ticket to heaven.
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post #2 of 19 (permalink) Old 01-07-2009, 06:00 PM
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What model/type engine are you working on? You should be able to just unbolt and remove the starter, then replace the gear. What are you talking about when you say magneto? Do you mean the Flywheel? In that case you should use an impact gun to break the bolt loose, or if you don't have an impact, you can use a pipe wrench on the pto shaft and jam that up against something to lock the motor up. Bolt is left to loosen, right to tighten.
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post #3 of 19 (permalink) Old 01-07-2009, 11:38 PM Thread Starter
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What model/type engine are you working on? You should be able to just unbolt and remove the starter, then replace the gear. What are you talking about when you say magneto? Do you mean the Flywheel? In that case you should use an impact gun to break the bolt loose, or if you don't have an impact, you can use a pipe wrench on the pto shaft and jam that up against something to lock the motor up. Bolt is left to loosen, right to tighten.
Sorry about the lack of info. I'm not sure of the model number but it's a Murray Riding lawn mower. the engine is manufactured by briggs and stratton and has an electric starter. I believe it's 5HP.

By magneto I mean (magneto armature/fan) which bolts to the top of the crank. It would be located just under the pull starter if this model had one.

Again, I have tried to place a pipe wrench on the PTO shaft located at the bottom of the engine while applying torque to the bolt. The PTO shaft breaks free before the bolt does. I have also tried using a pry bar to keep the armature from turning but can't get a good bite. I would like to keep from having to buy an impact as I am doing this work for free. And I would much rather they use the push mower than me spending money for something I have no need for.

I was hoping someone here would know some secret technique

Think I'm going to try and find a strap I can tighten around the fan/armature to prevent it from moving.
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post #4 of 19 (permalink) Old 01-08-2009, 07:20 PM
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Ok I believe your referring to the flywheel which sits on top of the engine crankshaft, the armature is under the flywheel for the charging system and Briggs and stratton does not use Magnetos. Just an ignition coil, and point if you have an older model.
Anyhow you don't have to remove the flywheel to change the starter gear, just unbolt the starter, remove it and change the gear.
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post #5 of 19 (permalink) Old 01-08-2009, 09:04 PM Thread Starter
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Ok I believe your referring to the flywheel which sits on top of the engine crankshaft, the armature is under the flywheel for the charging system and Briggs and stratton does not use Magnetos. Just an ignition coil, and point if you have an older model.
Anyhow you don't have to remove the flywheel to change the starter gear, just unbolt the starter, remove it and change the gear.
I'm not a Briggs and Stratton expert but this Briggs and Stratton engine has an armature and magneto. And bolted to the bottom side of the armature is a nylon gear ring which turns the crank when the starter engages the bendix. I have inspected the bendix and it doesn't need to be replaced, seeing how it is made of steel.

You seem to keep going off topic. I never said anything about the starter, why do you keep bringing it up? I need to break the bolt, that holds the armature/fan assembly to the crank, free. You acted as if you didn't know what a magneto was in your first post now your telling me B&S doesn't use them. I can't help but question the accuracy of your advice about this bolt having right handed threads.

Look dude I appreciate you sparing me your time. My bro-n-law can use the push mower or buy a new riding one. I'm washing my hands of it.
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post #6 of 19 (permalink) Old 01-08-2009, 09:57 PM
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I know what you are talking about. The ring on the bottom of the flywheel must be broken. If we had the model # and the type, we could look up what kind of flywheel you have and see if the ring is replaceable,some are. If you go to www.partstree.com and look up your engine you'll find a picture of your engine or give it to me with the no. and I'll look it up for you.
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post #7 of 19 (permalink) Old 01-08-2009, 10:13 PM
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In the matter with not being able to get flywheel nut off,put a pipe wrench on the bottom end of crankshaft (brace it to something so it won't turn or have your B-L hold pipe wrench) then try using a socket and rachet to remove nut,if the only tool you have is the pipe wrench then use that. Hope this helps. We try to be Minnesota Nice to everyone>
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post #8 of 19 (permalink) Old 01-09-2009, 01:08 AM
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Hey Kratos, I think what your asking is how to hold the flywheel (the fan thing on top of the engine) while trying to undo the nut that holds it on. You could try a "strap" wrench which is a handle with a rubber strap that you wrap arond the entire flywheel fan and then insert the loose end back into the strap wrench's handle. A strap wrench can be bought for around $10 at most any good harware store. Make sure you get one with a long enough strap.

That should let you get the flywheel/fan off and replace the starter gear ring. If I'm understanding you correctly you are saying the BIG 12" diameter gear is bad, not the little 2" gear on the starter motor? Right? Hang in there we haven't lost any mowing time yet.

-Maytag
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post #9 of 19 (permalink) Old 01-14-2009, 08:16 PM
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Hey Kratso 1963- how are you coming with that flywheel ring,you didn't give up did you?
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post #10 of 19 (permalink) Old 02-06-2009, 02:04 PM Thread Starter
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Question

Still trying to locate "strap" wrench thingy. Lowe's has one put it's to small. Going to continue to look for this tool.

I have tried putting pipe wrench on PTO shaft on bottom of motor. It, PTO shaft breaks loose before bolt on flywheel does. Going to put mower on jack stands and take off PTO and see if there is a place to put pipe wrench on Crank shaft.

Thanks for your input guys.
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post #11 of 19 (permalink) Old 02-06-2009, 07:11 PM
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Still trying to locate "strap" wrench thingy. Lowe's has one put it's to small. Going to continue to look for this tool.

I have tried putting pipe wrench on PTO shaft on bottom of motor. It, PTO shaft breaks loose before bolt on flywheel does. Going to put mower on jack stands and take off PTO and see if there is a place to put pipe wrench on Crank shaft.

Thanks for your input guys.
DO NOT DO THAT, you DO NOT want to chew up your crankshaft

you could make your own strap wrench out've a heavy duty ratchet strap
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post #12 of 19 (permalink) Old 02-06-2009, 07:53 PM Thread Starter
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DO NOT DO THAT, you DO NOT want to chew up your crankshaft

you could make your own strap wrench out've a heavy duty ratchet strap
Good Idea, I'll give that a try. THanks
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post #13 of 19 (permalink) Old 02-06-2009, 09:01 PM
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the strap wrench is sold at SEARS,,, works well, they have 2 sizes.
if possable take the mower to a service station and ask the guy to take the nut off for you, using AIR tools
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post #14 of 19 (permalink) Old 02-13-2009, 10:53 AM
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You mentioned that the flywheel ring gear is nylon, and the bendix on your starter is steel. That is the problem. The flywheel was available with aluminum, nylon, or steel ring gears. The only time a steel pinioned starter should be used is with a steel ring gear. A plastic pinion gear is used with aluminum and nylon ring gears. You should be able to replace ring gear, and just the pinion on the starter ( the whole starter does not need to be replaced ). A strap wrench is the recommended tool. Make sure to cover all the magnets underneath the flywheel before you attempt to drill out the steel rivets that hold the ring gear to the flywheel or you'll be picking the shavings out for a long time. I'm pretty sure the ring gear kit includes repacement nuts and bolts to replace original rivets, a replacement pinion gear, and pinion gear retainers (roll pin, and c-clip). Hope this helps!
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post #15 of 19 (permalink) Old 01-26-2010, 08:48 PM
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The really tough part may be getting the flywheel to release from the shaft. Apply penetrating oil to shaft after removing the nut and let set over night. Purchasing a flywheel removal tool is a good idea. Install the tool in the provided threaded holes in the flywheel near the shaft and tighten a bit. Tools vary in design, but tapping the center of the shaft lightly with a hammer as you tighten removal tool to cause a vibration to loosen shaft is a good idea to prevent breaking something. I almost always just tap the center of the shaft with a hammer with slight pressure applied to bottom of flywheel with a large screwdriver and keep turning the flywheel after each tap, but I have done that enough to know how much pressure I can apply without cracking the block.
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