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.
At first, I leveraged UP with the prybar on the aluminum engine, then moved about 60 degrees and leveraged again (all the while uselessly banging DOWN on the flywheel puller contraption from ACE on the flywheel).
When I moved the third 60 degrees, I didn't realize it but now I was at the front of the mower where the carberator and air filter are, which has a plastic pipe (painted the same color as the aluminum engine) which is the intake manifold.
In just a split second, the plastic pipe collapsed, along with a bolt which snapped in half holding it to the opening for the intake valve.
It was exactly at that point where I realized the advice to bang DOWN on the crankshaft while lifting UP on the flywheel (thereby leveraging DOWN on the soft engine parts) was sheer folly.
It was only then I started wondering about the logic of it all. Of course, prying UP makes sense to remove a flywheel ... but what does banging on an immovable crankshaft going to do?
I wonder WHERE it goes as there is nowhere "down" to go.
One end of the crankshaft is sticking up in the air with the nut loosly put back on (to protect the threads) while the other end is firmly attached to the lawn mower blade. The piston is in the middle.
Where "down" can it go?
That's a LOT of distance for an immovable flywheel. Do you bump it back UP
1/8th of an inch when you reassemble?
I agree. What everyone said (and what utterly failed for me) was to pry UP on the flywheel and bang DOWN on the crankshaft.
What worked (for me) was to tap the pre-existing holes and lift up on the flywheel leveraging on the center of the crankshaft with a harmonic balancer puller with two 1/4 x 20 bolts and washers (that bent like potato chips from the force). :)
While this shock and awe effect didn't work for me, I do understand what you're implying.
Basically, from Physics 101 back in college, dynamic friction is less than static friction.
So, what you're saying, I think, is by banging on the flywheel (actually banging on anything would work as well), you set up vibrations, which allow things to move with just a little bit less friction.
Well, at least that explanation makes sense. It didn't work. But it makes sense! :)
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:
One said the vibrations lessen the friction slightly ...
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?
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.
The vibrations loosen the fit between the flywheel and the crankshaft.
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).
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! :)
Someone else mentioned the vibration/shock of whacking something with a hammer. It's an old trick that works for things like plumbing. Hold one hammer on one side of the plumbing, hit the other side with another hammer. Doing it in as many places as possible loosens up the fittings. Hitting a bolt head sometimes helps loosen it. It's seldom that I hear of things vibrating tight. If nothing else whacking something with a hammer a few times is a good stress reliever.
I'll have to snap some pictures though, as you'll need to see that if you're going to go 360 degrees around the flywheel, you have to pry on SOMETHING in all directions and the intake manifold was in front, across the entire front of the engine, crossing from the air intake on one side to the valve mechanism on the other side.
Of course, if I knew that dirty gray pipe crossing the front of the engine was brittle plastic, I would have given up on the pry-bar method. Besides, knowing what I know now, nobody in his right mind would pry on anything to get this type of flywheel off.
The right way to do it, I found out belatedly, is to tap the two pre-existing holes with a 1/4x20 tap and simply use a harmonic balancer to lift the flywheel up almost effortlessly. The force is high, but the effort is low due to mechanical leverage.
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.
You don't pry to move the flywheel. You pry to move the crankshaft up a bit to give it room to move down when you tap. Will saying it the second time get it through to you?
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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