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

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• posted on July 13, 2010, 12:51 am

On Mon, 12 Jul 2010 16:27:15 -0700, Oren wrote:

Mea culpa on the banging of the flywheel. I meant on the crank.
So far, this "tradition", passed down by generators, has the following logic:
1. One said the vibrations lessen the friction slightly ...
2. Another said it moves the crankshaft DOWN 1/8 of an inch ...
I wonder if you actually do move the crankshaft down by 1/8 of an inch, where does it go? At one end is the flywheel; in the middle is the piston; and the other end has a blade attached.
If it moves down 1/8th of an inch, where does all that go? Do you move it back UP 1/8th of an inch when you put the new flywheel back on?
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• posted on July 13, 2010, 2:11 am
On Mon, 12 Jul 2010 17:51:18 -0700, "James H."

When you hit the crank -- do it with the mower on the lawn turf. That is what takes up the shock, No the crank will _not_ move 1/8" -- forget that!
Soil will cushion the blows better than a driveway.
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• posted on July 13, 2010, 4:23 am

Again, the one who said 1/8" misspoke. It is only a few thousandths.
Harry K
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• posted on July 12, 2010, 5:44 pm
James H. wrote:

If after everyone answers you for the second time, you will either now understand, OR you should come to the realization that you have no knowledge and no apparent learning ability for basic mechanics and physics. And along with that understanding, you will admit to yourself that you picked a stupid ass place to pry and your broken intake is your fault and not due to anyones suggestions here.
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• posted on July 13, 2010, 1:00 am
On Mon, 12 Jul 2010 13:44:23 -0400, Tony wrote:

Well, I've taken Physics 101 in college, so, I have a basic understanding of static and dynamic friction. But I don't disagree that the explanations given so far are, shall we say, problematic.
So far (please correct me if I state this incorrectly), we have (only) two different reasons proposed for banging down on the crankshaft.
1. The vibrations loosen the fit between the flywheel and the crankshaft.
2. Moving the crankshaft down 1/8th of an inch, in effect, moves the flywheel up 1/8th of an inch.
Assuming these are the only proposed reasons (again, correct me if I err), I reply that both answers are "understandable"; but both are problematic.
The problem with hypothesis #1: - If vibrations are what we're after, we could just as well (and perhaps more safely) smack the red shroud on the lawnmower; or smack (lightly) the flywheel itself; or smack the sturdier lawnmower blade. I guess vibrating the crankshaft from the top is easier than vibrating the crankshaft from the bottom; but what I'm saying is that vibrations don't have to come directly from the top of the crankshaft. In my case, it wasn't anywhere near as successful as simply pulling the flywheel up.
The problem with hypothesis #2: - If moving the crankshaft DOWN is the goal, well what do you do when you're done? Now your crankshaft is 1/8th of an inch too low. Do you pop it back up from the blade side? If I understand the engine correctly, the flywheel is on one end of the crankshaft and the blade is on the other, with the piston in the middle. If you move the crankshaft down 1/8th of an inch, aren't you moving the entire apparatus down 1/8th of an inch? Don't you have to then move it back UP 1/8th of an inch?
Having said all this, I do recognize MANY people bang down on the crankshaft (just as people kick the tires of used cars for some reason); I just can't fathom any practical reason for the type of engine that I have (which is designed to be removed by tapping the pre-existing flywheel holes and pulling up leveraging down on the crankshaft).
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• posted on July 13, 2010, 3:17 am
James H. wrote:

Whoosh!!!!
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• posted on July 13, 2010, 4:32 am

And very repeatedly. That wall should be almost destroyed by now.
Harry K
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• posted on July 13, 2010, 3:49 am
James H. wrote:

Why don't you just admit that you were not able to do what thousands of other people do successfully quite often, and to make matters worse, you also broke something else in the process?
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• posted on July 12, 2010, 6:05 pm

For the answer to this, you only need to look at Newton's laws of motion.
Newton's first law, an object at rest will tend to stay at rest... applies to the flywheel. When you smack the crankshaft, the flywheel will want to tend to stay in place, while the rest of the lawn mower will go in the direction of your hit.
You are basically knocking the mower out from under the flywheel. Why? You can't hit the flywheel to knock it off the mower so this is your only choice.
As for breaking the intake manifold, that's your fault. You should've looked before prying. Pry on something that isn't the intake manifold.
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• posted on July 12, 2010, 6:53 pm

The tapping also seems to aid the penetration of oil into the joint, I feel. A flywheel puller is a much safer choice, since the banging on the crankshaft also places large lateral loads on the bearings of the engine. Rather than whack with a 3# hand sledge, I prefer a 22oz ball peen hammer and some penetrating oil to see if I can get things moving.
Also when tapping on the shaft, I always run the nut up until it's flush- to just a bit proud- of the shaft end. That helps to keep the shaft end from swelling or messing up the threads, I feel.
My friend had a wood chipper with a very sturdy, steel, pulley on the output shaft of his engine. The pulley had to be removed to do some other work on the engine. I had my flywheel puller on and tightened about as good as I felt reasonable. I also did the penetrating oil and tapping on the shaft (via the puller's bolt) to no avail. Enough was enough.
My friend and I used our Mapp gas torches to heat the pulley for a few minutes while we dripped some water onto the motor's shaft. I tapped the end of the shaft lightly, and the pulley came right off. I doubt if you can do this with a flywheel, but it sure works with substantial metal stuck to a shaft.
Nonny
--
On most days,
it's just not worth
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• posted on July 13, 2010, 1:03 am
On Mon, 12 Jul 2010 11:05:38 -0700 (PDT), snipped-for-privacy@rochester.rr.com wrote:

I don't disagree with you ... that it's my fault for breaking the intake manifold by prying down on it.
What I learned is that this engine (at least) isn't designed for prying up and banging down.
It's designed for you to tap a 1/4 x 20 thread into the two pre-existing holes in the flywheel and simply pulling the flywheel off with a harmonic balancer pulley.
I'll snap some pictures and post them so you guys can see all this.
Mostly I want the next poor guy to get the point that smacking down on the crankshaft and pulling up on the flywheel might not be the first choice for engines such as my Briggs and Stratton Craftsman lawnmower! :)
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• posted on July 13, 2010, 1:27 am
On Mon, 12 Jul 2010 18:03:06 -0700, James H. wrote:

Mechanics have been using the pull up, smack down method for maybe 60 years. I have a puller and I have a device that screws on the crank to allow you to rap on it without damaging the threaded top of the crank. I've even just screwed the nut back on a few thread and gave the crank a rap. It's something you develop a feel for if you do it enough and having done it many times myself I can do it in my sleep and not damage anything. The part of the crank that the flywheel sits on is tapered a bit and this is why that initial jolt loosens the flywheel. If it wasn't tapered you would need to use a puller.
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• posted on July 13, 2010, 1:36 am
On Mon, 12 Jul 2010 18:03:06 -0700, "James H."

Now you make sense. Hammers are a last resort as a solution.
I still say smack the crankshaft....
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• posted on July 13, 2010, 3:19 am
James H. wrote:

If it was designed for that, the holes would have been tapped.
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• posted on July 13, 2010, 7:03 am
On Mon, 12 Jul 2010 20:19:40 -0700, Bob F wrote:

It IS designed for the flywheel puller and the holes are not tapped. We already pointed out this in the owners manual.
In addition, the Briggs & Stratton FAQ says to tap the holes with a 1/4 x 20 tap: http://engines.myfaqcenter.com/Answer.aspx?p_faqid422
This says it's dangerous (to the equipment) to smack the crankshaft. http://outdoorpowerinfo.com/repairs/flywheel_removal.asp
Read this: http://www.repairfaq.org/samnew/lmfaq/lmflyrml.htm It says the same thing.
This says to use the flywheel puller: http://www.ehow.com/way_5655790_briggs-stratton-flywheel-removal.html
The more I learn about this, the more I realize the "traditional" shock and awe method is wrong (and dangerous to the equipment).
Yes, it works (for those of you with experience); but it's not the proper method of removing the flywheel on this type of engine.
I'll post some pics for you guys to see.
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• posted on July 13, 2010, 3:50 pm
James H. wrote:

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• posted on July 13, 2010, 5:29 pm
On Tue, 13 Jul 2010 08:50:28 -0700, Bob F wrote:

Hi Bob F,
I'm sorry. I didn't realize that. My mistake.
I think we can all agree there are two ways to remove a flywheel: 1. Pry and bang 2. Tap and pull
The advice to pry and bang, for someone like me (I always said this was my very first lawnmower engine), is, let's just say, "problematic". :)
In my case, using that method cost me a broken intake manifold and bolt, and time, and money ... which would have been better spent doing it the right way (i.e., the documented method, documented right on the flywheel, unbeknownst to me!). :)
So, I strongly recommend that people new to lawnmowers use the proper approach, which is to tap the two holes and pull with a flywheel puller (I used a harmonic balancer puller available at any auto parts store).
In the end, it would have been less time & money had I done the job properly. Too bad I didn't notice, in all the dirt and grime, the words clearly stamped (now that it's clean) on the flywheel (see the pictures posted at http://yfrog.com/jobriggsandstrattonflywhej ):
TO REMOVE (flywheel), USE WHEEL PULLER HOLES
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• posted on July 13, 2010, 8:47 pm
James H. wrote:

There's an art to knowing what forces you can apply where on mechanical devices. You have just learned a bit of that art. I started over 50 years ago. The next time, you will know better. It might not be a flywheel, but you will think about what can be damaged a little more carefully, and hopefully avoid damage. Sometimes learning is harder than other times.
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• posted on July 13, 2010, 3:46 am
On 7/12/2010 8:03 PM, James H. wrote:

BUT it is the first choice. And if you had a B&S manual, you'd see that.
--
Steve Barker
remove the "not" from my address to email
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• posted on July 13, 2010, 7:04 am
On Mon, 12 Jul 2010 22:46:34 -0500, Steve Barker wrote:

B&S says first choice is the flywheel puller: http://engines.myfaqcenter.com/Answer.aspx?p_faqid422