What is the logic of banging DOWN on a crankshaft to remove a flywheel?

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What is the logic of banging DOWN on a lawnmower crankshaft in order to lift a flywheel UP?
In another thread, I asked about how to repair a lawnmower that hit an obstruction and started running badly and then not at all. You guys correctly ascertained it was a bent flywheel pin (mine was shaped like a Z).
I tapped two holes in the flywheel with a 1/4x20 tap and easily removed the flywheel with a harmonic balancer puller but only after I broke the intake manifold in half trying to bang down on the crankshaft as I pryed up with a pry bar.
In the end, I conclude that banging down on the crankshaft and prying up with a pry bar is the wrong advice ... (1) Prying up with a prybar can easily destroy the intake manifold, for example ... (2) Banging down on the crankshaft appears useless to me
My question: Why do people recommend banging DOWN on a crankshaft when you want to move the flywheel UP?
What's the logic?
The crankshaft isn't going to go down and the flywheel isnt' going to go up when you bang on the crankshaft. It appears, to me, to be a useless endeavor.
But, since so many people have said to bang DOWN on the flywheel ... may I ask what is the logic in that?
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James H. wrote:

I usually pry up "firmly" on the flywheel on two side (wooden wedges work well), then tap downward on the end of the shaft (with the nut loosened to be flush with the crank end). By lifting up, you raise the crankshaft slightly, takeing up any play. Then when you tap the crankshaft, it applies instantaneous force way higher than you could ever get by lifting the flywheel. The mass of the flywheel resists the momentary force, so the crankshaft loosens.
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Bob F wrote:

Yep, that's the way I have always done it as well. They actually sell a tool that is threaded onto the end of the shaft so that the end of the shaft is protected from the hammer. In other words, the manufacturer has it as a recommended procedure.
Jon
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I agree with the others. Even using a puller you still tap the bolt that is pushing on the crankshaft after you put a little pressure on it. If it don't loosen, a little more tightening and another rap with the hammer.
If you broke your manifold, you were using too much leverage in a bad location. Looking for a place to use leverage is another trick sometimes.
Now, if you drilled holes in the flywheel you may have knocked it out of balance. Check balance before re-assembling.
Hank
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I use a puller but I also hit the top of the puller a few times after I have gotten some tension on it. Frees up the flywheel.
They make pullers that are wider and have hooks on the ends. But nothing wrong with drilling a couple holes.
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On Mon, 12 Jul 2010 04:42:02 -0700 (PDT), jamesgangnc wrote:

As you said, I tried a three-pronged 8-inch gear puller, which is, as you noted, something that grabs the sides of the aluminum flywheel; but after seeing the flywheel actually bend upward, I gave up on that method also as too dangerous. It would have cracked the flywheel in half.
Only then did I realize the simplest answer of all, which was to tap the two pre-drilled 1/4x20 holes and simply use a two-bolt harmonic balancer puller - and the flywheel simply popped off without any effort whatsoever.
End result is: 1. It's crazy to bang DOWN on the crankshaft and pry up on the flywheel 2. It's crazy to lift the EDGES of the flywheel with a gear puller 3. The right way is to lift near the CENTER of the flywheel with a puller
I still don't get the logic of banging down (momentarily deformed crankshaft?); but I haven't read all the responses yet.
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On 7/12/2010 6:45 PM, James H. wrote:

This moron is just not going to get it. We're done here.
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Thank you, Doctor. I concur.
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On 7/12/2010 6:45 PM, James H. wrote:

Here, maybe after you watch the proper procedure a few dozen times, you'll get it:

http://www.youtube.com/watch?v=2zmD_buI5xA

Just watch this over and over and over.
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On Mon, 12 Jul 2010 16:45:57 -0700, "James H."

Replace the flywheel now. Dangerous? Wait until it fly's apart and hurts. Caused by fracture in cracks.
Never pull a mower flywheel without the tool, or without hitting the crank.
Outside "hooks" will crack the flywheel. The reason your flywheel bent!
Learn some tradition, I say.
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On Mon, 12 Jul 2010 18:54:50 -0700, Oren wrote:

Hi Oren, I don't disagree with you on replacing the flywheel (I ordered one from Sears in fact, but didn't mention it because it wasn't relevant to the discussion).
However, please realize, that "tradition" is apparently dead wrong here.
This is tradition: http://www.waldeneffect.org/blog/Briggs_and_Stratton_flywheel_removal /
However, the owners manual begs to differ with tradition: http://www.google.com/url?sa=D&q=http://www.managemylife.com/mmh/lis_pdf/OWNM/L0505023.pdf&usg QjCNH2N8YjjLyskja0QyfRWxQAo5_C_A
The ONLY way to remove this type of Briggs & Stratton flywheel is to tap the pre-drilled holes and lift up with a two-bolt harmonic balancer puller, the lifting force being near the center of the flywheel and the indented tip of the crankshaft.
The "flywheel puller" is part #363 (Sears part number 19069, Briggs and Stratton part number BS 19069) on page 38 and 39 of the Owner's Manual for the Craftsman Rotary Lawn Motor, 6.5 Horsepower, 21" Rear Discharge, Model No., 917.388853 with the Briggs & Stratton 4-cycle engine, model number 123K02-0444-E1.
Here is the flywheel puller for $7.50 online: http://farmex.now.tc/catalog/product_info.php?products_id#68
It's sheer folly to try to bang the flywheel off with shock and awe. http://www.briggsracing.com/en/articles/tool-of-the-month/using-flywheel-puller.aspx
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On Mon, 12 Jul 2010 23:42:20 -0700, "James H."

Even if you DO use a puller, you STILL bang on the crankshaft as you GENTLY and GRADUALLY apply pressure with the puller.
Flywheels are surprisingly delicate
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On 7/13/2010 1:42 AM, James H. wrote:
<drivel snipped here>

WRONG WRONG WRONG again. That is not the only way. Actually, it's not a way at all. Those holes are not tapped, so therefore a puller can't be used.
<rest of the drivel snipped>
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James, the bottom line is, people have used the "hit with hammer and pry" method for years w/o doing any damage to whatever they are working on.
I used that method to remove everything from AC compressor clutch/ pulley assembles, to wiper blade arms on some GM cars that are have Loctite on the shafts they are bolted on to.
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James H. wrote:
> but after

You saw it bend? They don't do much bending, but they do crack. Throw it out, you ruined it.
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On Mon, 12 Jul 2010 00:56:54 -0700 (PDT), Hustlin' Hank wrote:

The holes in the Briggs and Stratton 3.5 HP engine flywheel are pre-drilled by the manufacturer. All I needed to do was tap them.
I don't think tapping the two holes (1/4x20) will knock them out of whack; do you?
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I followed that thread and you were given clear, explicit explanations of why it works and also that it is a common method of accomplishing the goal.
Harry K
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On Mon, 12 Jul 2010 06:18:14 -0700 (PDT), Harry K wrote:

Hi Harry K, I might have been given clear explicit explanations; but that doesn't mean I understand the logic of banging down on the immovable crankshaft.
The fact that so many people suggested that "common method", yet the experience I had (where it couldn't possibly work) is what confuses me.
I fully appreciate prying UP on the flywheel (although, as my experience dictates, that's the absolutely wrong approach for this Craftsman 3.5 HP Briggs and Stratton lawn mower engine).
So far I've heard that banging down on the flywheel "momentarily deforms" the crankshaft ... and that ... somehow ... magically? ... allows the flywheel to pop up on the tapered shaft.
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James H. wrote:

Every mower I've done this to has been a B&S engine. And it has always worked. Sometimes quicker than others, but every single time. And I've never broken anything.
But then, I was never reefing on the pry bar, since to only point is to lift the crank by whatever play it has so it can move when you tap. Each time you tap, the flywheel lifts a tiny bit, until it pops loose.
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On Mon, 12 Jul 2010 20:29:12 -0700, Bob F wrote:

Hi Bob, On the Briggs and Stratton web site, they explain the use of the flywheel puller.
In the owners manual, they show a picture and the part number for the flywheel puller.
While I definitely see "tradition" has it that almost everyone (except Sears and Briggs and Stratton) recommends banging on the flywheel, that's NOT the way to remove the flywheel on my Craftsman Briggs and Stratton engine! :)
This video shows the (wrong) traditional method: http://www.waldeneffect.org/blog/Briggs_and_Stratton_flywheel_removal /
This is the $7.50 flywheel puller (Briggs & Stratton P/N: BS 19069): http://farmex.now.tc/catalog/product_info.php?products_id#68 http://tewarehouse.com/7-05979 http://www.jackssmallengines.com/service_tools2.cfm
The owners manual (page 38 & 39) show this as Sears P/N: 19069: http://www.google.com/url?sa=D&q=http://www.managemylife.com/mmh/lis_pdf/OWNM/L0505023.pdf&usg QjCNH2N8YjjLyskja0QyfRWxQAo5_C_A
Point is, banging on this type of Briggs & Stratton engine is sheer folly when there is a perfectly cheap and effective method.
Even the Briggs and Stratton web site says (at least for their racing engines) the ONLY way to remove a flywheel is to use a flywheel puller.
So, I'm just letting folks know the lessons learned. I asked. I got advice. Most of it was wrong. But some of it was dead on right. I made mistakes. I learned. I found out, the hard way, the right way. And I'm letting folks know.
The only thing that had confused me was how the old way was supposed to work (logically that is) ... and it turns out that it does work ... but it's the wrong method to use for these Briggs and Stratton engines.
I need to post some pictures instead of responding with text. :)
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