Hi, I couldn't find a small engines newsgroup so here I am. I just
installed a pulley on a 5.5 HP Honda engine for a cement mixer. The
drive shaft and pulley are "keyed" so they gave me a 3/16 square rod
from which to cut the key.
I cut the key, slid on the pulley, pounded the key in with a hammer,
and cut the key flush with the end of the shaft. There is no setscrew.
Then it occured to me: If I ever wanted to remove the pulley how in the
hell would I remove that key? It's a really tight fit. How is this
PS. There is maybe 1" clearence between the engine and the backside of
You pull off the pulley and then pull the key straight out.
BTW those keys are normally filed to a nice fit. However, pounding yours in
won't have hurt anything but it may have malformed the keyseat slot slightly.
The key prevents rotation, the pulley is secured to the shaft on a taper.
To remove, a puller is used. Arms grip the pulley and a bolt is turned
against the shaft.
Tapers are a common way to secure something to on in a shaft. An other
common example would be how a drill chuck is fit into a lathe or a drill
So how should I have done it?
The tech at the parts place said the keys are made to be tight, they
will not just slide in by hand --unless he was handing me a bunch of
BS. I just checked and the key rod is marked as 3/16" and the
published specs of the key ways are each 3/16 x 3/32. I hand ground a
slight taper on the end of the key just to get it started. Did I do
A "properly fitted" (YMMV) key, should be a snug slip fit in both the
pulley and the shaft.
Lay a piece of 400 grit sand paper on a flat surface, and making
figure 8s, gently "lap" the key until its a snug slip fit into the
Then slide on the pulley on. A bit of Dychem or even a quick wipe
down with a magic marker will show if/where things are dragging.
Be sure to keep your orientation. Side to side fit in both the shaft
and the pulley is far more important than top to bottom. Particularly
if the set screw bears on the key. A key is to prevent rotary play
between the shaft and the pulley. If play develops..it will deform the
key and the key will either shear in half, or worse..beat the shit out
of the loose part..either the shaft or the pulley.
I repaired a Clausing Variable speed drill press a couple weeks ago.
The keyway in the pulley was perfect..however the keyway in the shaft
extended 1/3 the way around the shaft. The key..looked like a
The only thing I could do was pull the rotor, remachine a new keyway
halfway around the shaft, fit up a new key (slip fit as described
above) and put it back into service.
When you hammered the key in..you probably swoll up the keyway in the
pulley, if it were softer than the shaft, or visa versa. You are
probably ok, in your application, its not going to get used 24/7 in a
production machine shop. But its really bad form to use a hammer for
Unless you are a carpenter or a black smith...
"That which does not kill you,
has made a huge tactical error"
You will find that admitting ignorance and then carefully considering
replies around here will cause the most cranky old farts to soften and give
you an explanation. I suspect that they just want to know you are listening
to what they are saying. If they think you think you know it all, you are