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

[James H.]

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?

[Bob F]

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.

[Jon Danniken]

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

[Hustlin' Hank]

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

[jamesgangnc]

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.

[Harry K]

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

[hrhofmann]

Why were you anywhere near the intake manifold, you should have been leveraging against the main chassis of the engine!!!

[Stormin Mormon]

Try it.... has worked for me, for years. Yes, the crank shaft goes down.

The fit between the flywheel and the crankshaft is a slow taper. You only have to bump the crankshaft down 1/8 inch or less, and then the friction fit between the two shears. And the flywheel lifts off.

I rather doubt that anyone has advised to bang down on the flywheel.

[Jeff The Drunk]

They make a tool you can screw on the end of the crank to bang on so you don't mess up the thread at the top. The physic is shock as in an impact wrench will drive the screw tighter or looser with less effort and less chance of breaking things. In the plumbing business there is the term "warming up a pipe joint" when using steel pipe and fittings to loosen the joint by banging on it when you can't wrench it apart. Same thing with a lid on a glass jar that you can't loosen. Smacking it down on a hard surface loosens it enough that you can then unscrew it. They are all interrelated.

[Oren]

Tradition.

Passed down by generations.

[Tony]

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.

[mkirsch1]

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.

[Nonny]

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

[DerbyDad03]

re: "Same thing with a lid on a glass jar that you can't loosen. Smacking it down on a hard surface loosens it enough that you can then unscrew it. They are all interrelated."

I dunno...

I always smack the bottom of the jar with the heel of my hand and listen for the "crack".

It's my understanding that that releases the vacuum that keeps the jar sealed tight.

I'm guessing that there is no vacuum involved in the removal of a fly- wheel.

[salty]

You can also remove the cork from a wine bottle by banging the bottom of the bottle sharply, several times. The cork will pop out. Be careful not to break the bottle!

[JIMMIE]

Should read, "What is the logic of prying against your intake manifold"

[Stormin Mormon]

And misquoted by some. Mower repairmen don't bang down on the flywheel.

[Oren]

The OP's subject is bangin' his crank. He mis-spoke about the flywheel.

No one suggested he bang the flywheel

Like I said before, it's tradition to bang on the crank.

[James H.]

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?

[James H.]

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.