| The following is how I deal with removing badly stuck Gib keys.
1. If the crankshaft is firmly rusted to the flywheel, eccentric,
coupling etc. I ask myself does this item have to be removed? One should keep in
mind that when removed the clearance (or fit) to the shaft may be such that
the item may no longer be tight and in the case of a flywheel it may result
in it being so loose that it is no longer safe to use operationally. In
the case of an eccentric or coupling these items can be secured with one of
the Lock Tite, compounds whereas the flywheel would be too dangerous to operate
probably even at low idle RPM. About 1900 many marine engine makers began switching to split
crankcase designs as they learned that the end bell style housing caused them to
break or bend too many flywheels and crankshafts. The split crankcase along the
crankshaft centerline permitted rebabiting the crankshaft bearings without
removing the flywheel etc.
2. Too often the GIB key has been badly abused to the point that there is
little left of the tang to work with. I will deal with that a little later.
Taking the case of the GIB key that has enough of the tang to work with first. If the engine is a small engine with a disk as apposed to a
spoked flywheel I support the rim of the Flywheel so the weight of the engine is
carried on the rim with just enough clearance to the floor so that if something breaks loose the engine won't drop far and break something. If
it is a bigger engine then this is not a good approach. In that case I work
with it in its normal operating position. I carefully scribe a fine line
on the key so the slightest movement can be instantly detected. Taking dental tools (my dentist gives me old tools she discards and they are
really good steel and ideal for engine restoration work) I carefully dig out the
rust along and around the key/keyway and around the shaft. I deburr the
keyway without enlarging the keyway appreciably. I then surface grind a
rectangular drift that is a close fit (.001-.002 inches) in the keyway.
The key end of the drift must have at least the same area as the head of the
key including the tang. This is important as the idea is to transfer the
blow of the hammer on the drift over the entire area of the key thereby minimizing the potential for serious damage to the head of the key.
The next step is to slide the drift into the keyway up against the head of the key. Hose clamps make good straps around the shaft to hold the
drift in the keyway. Start out with a easy rap on the drift. and see if the key
move in at all. If it has then use one of the penetrating fluids around
the key. If it has not move then progressively harder blows (but take it
easy) should at some point move the key. When it has moved at all this means
the rust bond around the key is broken and a penetrating fluid will then
easily flow into the joint. I have had little success with getting penetrating
fluid into a rusted joint unless it is first cracked. Do not drive the key in further. Move it only enough to be
detectable. Driving a Gib key too far in can crack a flywheel or other casting quite
easily. Once the key has moved the next step once the penetrating fluid has had
a chance to work is determined by how far from the face of the flywheel for
example the Gib key tang is. If you are lucky and it has 3/8th to 1/2 "
clearance and you can find a truck split rim tire tool simply position the
small curved end of the tire tool between the tang and face of the flywheel.
Lifting up on the tire tool should pull the key quite easily. If you cannot
find a split rim tire tool the next best alternative is a another large GIB
key on its side between the face of the flywheel and the Gib key tang. Driving the Gib Key on its side as a wedge should bring out the Gib key in
the flywheel. There are taper tools sold in the Gas Engine magazine that
will perform the same function as a large gib key. Generally Gib Keys are
not hardened and if the taper is too abrupt it may dig into the tang rather
than slide along the tang. It is easy enough to harden the key by simply
heating it up cherry red and dousing it in water. While not very professional it will generally harden the key enough so it slides rather
than dig in.
3. Taking the case of the badly messed up Gib key. Go through the same
steps as outlined above as far as driving the key in to break the rust seal.
Clean up the burrs and get penetrating fluid into the joint. Center punch
the end of the Gib key. drill and tap as large a hole as possible using a
National Fine thread tap, finishing with a bottoming tap. Rig up a support
on the end of the shaft so a steel threaded rod (threaded on both ends)
can be screwed into the key. Coat liberally the threads in the hole with an
anti-seizing compound. Try screwing the rod into the key until it bottoms
out. I seek to have about one inch of threaded rod in the key when it bottoms out. back it off a turn or two so if it should break in the
drawing out process you can then have a better chance of backing it out of the
hole with a left handed drill. On the outboard end of the rod put a couple
of washers under the head of a hardened nut. Make sure there is plenty of
anti-seizing is smeared on the rod and washers. Tightening the nut should
draw out the key.
4. If unhappy events show the messed up key really is a hardened key
then use the above treatment regarding driving it in and this time electrically
arc weld a steel rod to the top face of the Gib key after grinding the top
face flat so a good bond may be achieved. The slight amount of heat at this
point should not weaken the flywheel. Sometimes keys may be slightly work
hardened and using a small grindstone in a Dremel tool may permit getting
below the hardened surface. Try drilling a small hole in the top of the key
or take a file to it to see if it really is a hardened key.
5. Under no circumstance would I ever heat a flywheel hub to loosen the
rust bond. This practice is flirting with death and it will only be a matter of time when the flywheel disintegrates. The practice of .welding
iron casting is a specialize art and requires controlled furnace heating
and equally import controlled cooling. No amateur should attempt it in my
opinion. . .
6. In the case where there is no need to save the crankshaft I use a Saw
All with metal cutting blade to cut the shaft behind the flywheel trying
to leave at least 2" inches of residual shaft sticking out the aft face of
the flywheel. I then go through the same driving the key in until I detect
slight motion and if I can reach the key through the keyway on the aft face
of the flywheel I grind a rectangular drift and try to drive the key out
from the rear of side of the flywheel. If this isn't possible I clean up
the stub shaft and press the shaft through the flywheel from the rear. This
pushes the Gib key out of the flywheel keyway and relieves the pressure.
This won't work on a so called blind keys however. I have never seen a blind key on any small boat marine engine but there is probably one out
there somewhere just waiting to trip up the owner.
7. In any case whenever I am putting an iron casting like a flywheel in
a press I make up lead washers the same diameter as the hub to distribute
the pressure across the entire face of the hub. Typically the washers are at
built up from 1/8th inch thick sheet lead until there is about a 1/4 inch
thick pad. One 3 foot diameter flywheel took 35 tons to break the rust joint loose even after the Gib key had been removed and without the lead
pad it would have been destroyed. You have been warned!!
8. Now comes the real test! How do you know when you have driven home
the Gib key it is in tight enough but not so tight it will crack the hub?? I
have never found any text book or old timer that can answer that question.
What I do is drive it in until it seems tight and if possible I then drill
and tap the bottom of the keyway for a Allen set screw so the Gib key cannot
back out under operation. If there isn't enough space behind the head of
the Gib key I drill and tap through the top face of the Gib key. I have
never had a Gib key back out or a loose flywheel since I started using this
approach.
I hope this is some help. I learned it the hard way and the one thing
I have never done is heat a flywheel. I hope you don't either as you could
be passing a ticking time bomb on to another unaware of the danger they face.
Richard A. Day Jr. copyright
retained |
