I over-torqued four bolts in the lower unit of an outboard, and the
heads of three bolts broke off. I managed to remove one of the broken
bolt using a Dremel tool and a diamond grind bit. But I cannot remove
the other two broken bolts using the Dremel tool. Based on the past
posts in this newsgroup, I learn that the best option in this situation
is to drill out the broken bolts. I would like to learn the details of
the way to drill out the broken bolts. My question is:

Which size of drill bit do I need? Should it be as large as the hole
where the broken bolt is?

Related questions:

The bolts are for securing the water pump housing for the
impeller. The hole for the bolt is at the edge of the water pump base
-- meaning that one side of the hole is kind of thin -- something like
3/32" thick. The bolt itself is like 1/4" or slightly larger. Because
I have over-torqued the bolts, I found that the holes pretty much losed
most of the thread. If I drill out the bolts, I probably will find
that the holes will become even larger. If I re-thread the hole after
drilling out the bolts, I am afraid that the holes will be even larger.
I am afraid that there will not be enough metal left. Is my
estimation correct? I am wondering whether I may be better off somehow
pouring in new metal into the holes and drill new holes instead of
rethreading/enlarging the existing holes?

The other thing is that there is supposed to have a gasket on top
of the surface. I am wondering if I rethread and enlarge the holes,
there may not be enough metal at the edge of the water pump base to
bite into the gasket and prevent water from getting into the bolt. Is
this something that I need to worry about?

Thanks in advance for any info.

Jay Chan

wrote in message
ups.com...
I over-torqued four bolts in the lower unit of an outboard, and the
heads of three bolts broke off. I managed to remove one of the broken
bolt using a Dremel tool and a diamond grind bit. But I cannot remove
the other two broken bolts using the Dremel tool. Based on the past
posts in this newsgroup, I learn that the best option in this situation
is to drill out the broken bolts. I would like to learn the details of
the way to drill out the broken bolts. My question is:

Which size of drill bit do I need? Should it be as large as the hole
where the broken bolt is?


Call around to hardware stores and ask if they sell spiral screw extractors.
Before you jump in the car, measure the diameter of the bolt shafts you need
to remove. And, if you know the socket size that fits the heads, write that
down too.

JoeSpareBedroom wrote:
wrote in message
ups.com...
I over-torqued four bolts in the lower unit of an outboard, and the
heads of three bolts broke off. I managed to remove one of the broken
bolt using a Dremel tool and a diamond grind bit. But I cannot remove
the other two broken bolts using the Dremel tool. Based on the past
posts in this newsgroup, I learn that the best option in this situation
is to drill out the broken bolts. I would like to learn the details of
the way to drill out the broken bolts. My question is:

Which size of drill bit do I need? Should it be as large as the hole
where the broken bolt is?


Call around to hardware stores and ask if they sell spiral screw extractors.
Before you jump in the car, measure the diameter of the bolt shafts you need
to remove. And, if you know the socket size that fits the heads, write that
down too.

I tried that already. Either it didn't work or I went too easy on the
hammer. Anyway, it could not grab the bolt and could not spin the bolt
out. I attempted to drill one of the broken bolt away. But this
simply messed up the thread in one of the hole.

Finally, a copy of the Mercury Service Manual arrived last night. I
read it and realized that the water pump base could be removed just by
removing 6 bolts, and each broken bolt went through a threaded hole in
the water pump base into another threaded hole in the lower unit. Seem
like the threaded holes in the water pump base had some chemical
reaction with the bolts, and the threads in the hole in the water pump
base had completely corroded away (the thread on the bolt mating with
the threaded hole in the water pump base was also corroded away
significantly and that was part of the reason why the bolt head broken
off easily before the thread got damaged by being over-torqued). In
other words, the water pump base was not holding on the broken bolt,
and only thing that was holding on with the broken bolt is the threaded
hole in the lower unit, and I can remove the water pump base easily.
After I had removed the water pump base, I could see a large section of
the broken bolt sticking out in the open, and I easily removed them
using a channellock plier.

Is this a happy ending? Not really. In the attempt of drilling out
one of the broken bolt, I ended up messing up the thread in one of the
hole in the lower unit (the other three are fine). I don't know what
is the best way to deal with this. I will bring the lower unit to a
marine mechanic in this afternoon to see if he can help.

The other thing is that I can simply replace the water pump base and
the broken bolts, and this should take care of the corroded threaded
holes in the water pump base. But I am wondering why the holes and the
bolts can get so corroded. The bolts must be stainless steel, right?
I didn't know that stainless steel bolts can react to casted alumimum
lower unit. How should I prevent this problem from happening again?
Any idea? Thanks.

Jay Chan

wrote in message
ups.com...
JoeSpareBedroom wrote:
wrote in message
ups.com...
I over-torqued four bolts in the lower unit of an outboard, and the
heads of three bolts broke off. I managed to remove one of the broken
bolt using a Dremel tool and a diamond grind bit. But I cannot remove
the other two broken bolts using the Dremel tool. Based on the past
posts in this newsgroup, I learn that the best option in this situation
is to drill out the broken bolts. I would like to learn the details of
the way to drill out the broken bolts. My question is:

Which size of drill bit do I need? Should it be as large as the hole
where the broken bolt is?


Call around to hardware stores and ask if they sell spiral screw
extractors.
Before you jump in the car, measure the diameter of the bolt shafts you
need
to remove. And, if you know the socket size that fits the heads, write
that
down too.

I tried that already. Either it didn't work or I went too easy on the
hammer. Anyway, it could not grab the bolt and could not spin the bolt
out. I attempted to drill one of the broken bolt away. But this
simply messed up the thread in one of the hole.


Hammer????????

Call around to hardware stores and ask if they sell spiral screw
extractors.
Before you jump in the car, measure the diameter of the bolt shafts you
need
to remove. And, if you know the socket size that fits the heads, write
that
down too.

I tried that already. Either it didn't work or I went too easy on the
hammer. Anyway, it could not grab the bolt and could not spin the bolt
out. I attempted to drill one of the broken bolt away. But this
simply messed up the thread in one of the hole.

Hammer????????

Do you mean I am not supposed to use a hammer to work with the screw
extractor? I am under the impression that I am supposed to drill a
hole in the middle of the borken bolt, and hammer the screw extractor
down into the hole, and then use some kind of handle bar to lock on the
screw extractor and turn counter clockwise, and hopefully the screw
will back out. This was exactly what the owner of the hardware store
told me to do.

May be we are talking about two different types of screw extractors?
May be you are referring to the type that is like a drill bit, and we
are supposed to use it with a power drill (running in reverse) to dill
and back off the bolt? I could not use that type because the bolt was
sunken inside a small hole that the special drill bit was too large to
fit inside.

Jay Chan

wrote:
Call around to hardware stores and ask if they sell spiral screw
extractors.
Before you jump in the car, measure the diameter of the bolt shafts you
need
to remove. And, if you know the socket size that fits the heads, write
that
down too.
I tried that already. Either it didn't work or I went too easy on the
hammer. Anyway, it could not grab the bolt and could not spin the bolt
out. I attempted to drill one of the broken bolt away. But this
simply messed up the thread in one of the hole.
Hammer????????

Do you mean I am not supposed to use a hammer to work with the screw
extractor? I am under the impression that I am supposed to drill a
hole in the middle of the borken bolt, and hammer the screw extractor
down into the hole, and then use some kind of handle bar to lock on the
screw extractor and turn counter clockwise, and hopefully the screw
will back out. This was exactly what the owner of the hardware store
told me to do.

May be we are talking about two different types of screw extractors?
May be you are referring to the type that is like a drill bit, and we
are supposed to use it with a power drill (running in reverse) to dill
and back off the bolt? I could not use that type because the bolt was
sunken inside a small hole that the special drill bit was too large to
fit inside.

Jay Chan

The one I have seen had reversed threads so as you screwed it in, it
unscrewed the bolt

wrote in message
ps.com...
Call around to hardware stores and ask if they sell spiral screw
extractors.
Before you jump in the car, measure the diameter of the bolt shafts
you
need
to remove. And, if you know the socket size that fits the heads, write
that
down too.

I tried that already. Either it didn't work or I went too easy on the
hammer. Anyway, it could not grab the bolt and could not spin the bolt
out. I attempted to drill one of the broken bolt away. But this
simply messed up the thread in one of the hole.

Hammer????????

Do you mean I am not supposed to use a hammer to work with the screw
extractor? I am under the impression that I am supposed to drill a
hole in the middle of the borken bolt, and hammer the screw extractor
down into the hole, and then use some kind of handle bar to lock on the
screw extractor and turn counter clockwise, and hopefully the screw
will back out. This was exactly what the owner of the hardware store
told me to do.

May be we are talking about two different types of screw extractors?
May be you are referring to the type that is like a drill bit, and we
are supposed to use it with a power drill (running in reverse) to dill
and back off the bolt? I could not use that type because the bolt was
sunken inside a small hole that the special drill bit was too large to
fit inside.

Jay Chan


This is the type I was talking about. No hammer is used. The flutes of the
tool are deep enough that they grip without having to be forced into place.
http://www.mytoolstore.com/hanson/extractr.html

wrote
each broken bolt went through a threaded hole in
the water pump base into another threaded hole in the lower unit. Seem
like the threaded holes in the water pump base had some chemical
reaction with the bolts, and the threads in the hole in the water pump
base had completely corroded away

Take a look at a new water pump base for reference. I'll bet there aren't
supposed to be threads in the holes. (Doesn't make sense mechanically to run
a bolt through one threaded hole and into another.)

I ended up messing up the thread in one of the
hole in the lower unit (the other three are fine). I don't know what
is the best way to deal with this. I will bring the lower unit to a
marine mechanic in this afternoon to see if he can help.

The standard way to fix something like that is with a heli-coil insert.
http://www.emhart.com/products/helicoil.asp

Ernest Scribbler wrote:
wrote
each broken bolt went through a threaded hole in
the water pump base into another threaded hole in the lower unit. Seem
like the threaded holes in the water pump base had some chemical
reaction with the bolts, and the threads in the hole in the water pump
base had completely corroded away

Take a look at a new water pump base for reference. I'll bet there aren't
supposed to be threads in the holes. (Doesn't make sense mechanically to run
a bolt through one threaded hole and into another.)

I don't have a new water pump base yet. I will get it next week.

When I examined the holes for bolts in the old water pump base, I saw
thread in the holes. They were really corroded. Moreover, the bolts
also had thread in that area. And yes this is kind of strange; I am
wondering how the thread in the water pump base will match up with the
thread in the lower unit underneat the water pump base.

One possibility is that those "thread" in the old water pump base may
not be "real" thread. They may be a corroded surface that mirrors the
thread in the bolt.

I ended up messing up the thread in one of the
hole in the lower unit (the other three are fine). I don't know what
is the best way to deal with this. I will bring the lower unit to a
marine mechanic in this afternoon to see if he can help.

The standard way to fix something like that is with a heli-coil insert.
http://www.emhart.com/products/helicoil.asp

Yes, this is exactly what the marine mechanic proposed to me when I
brought the lower unit to his store. One question that I would like to
ask you: Do we need to re-apply the heli-coil insert whenever we
replace the bolt (like when we need to replace the impeller)? Thanks
for any info in advance.

Jay Chan

On 27 Oct 2006 06:56:13 -0700, "
wrote:

Yes, this is exactly what the marine mechanic proposed to me when I
brought the lower unit to his store. One question that I would like to
ask you: Do we need to re-apply the heli-coil insert whenever we
replace the bolt (like when we need to replace the impeller)?

Quoting from he

http://www.emhart.com/products/helicoil/standard.asp

"Screw-Lock Inserts positively secure threaded members against
loosening caused by vibration and shock. They have a high reusable
factor due to the exclusive HELI-COIL Resilient Screw-Lock which
permits frequent removal and reassembly of bolt without appreciable,
loss of torque."