Mea culpa on the banging of the flywheel. I meant on the crank.
So far, this "tradition", passed down by generators, has the following
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?
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" --
Soil will cushion the blows better than a driveway.
Logic can be from tradition.
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.
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).
For the answer to this, you only need to look at Newton's laws of
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
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.
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.
On Mon, 12 Jul 2010 11:05:38 -0700 (PDT), firstname.lastname@example.org 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
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! :)
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.
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
This says it's dangerous (to the equipment) to smack the crankshaft.
It says the same thing.
This says to use the flywheel puller:
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.
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
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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