What is the best way to loosen up the head bolts on a cylinder head on
an O.S. 40 engine? I tried a gentle turning with an allen wrench and
the bolts are on pretty solid. What would be the way to loosen the
On Wed, 03 Oct 2007 14:34:34 -0700, I said, "Pick a card, any card"
and goodfella instead replied:
I'd suggest that you first use the very tightest fit of wrench that
you can beg, borrow or buy. That way you won't risk making the
insides round by accidental slip of the hand.
Then, clamp the engine in a vice with rags wrapped around it leaving
the head exposed. Using firm, steady pressure on the bolts should do
the trick. They'll make a nice loud snapping/squealing sound when
they go and if your knuckles are exposed to something like the edge
of your workbench you may suffer a bit for your hobby.
For stubborn bolts, I have used a product that is available for
electronics work called Freez-Mist, used for cooling components to
see if they fail under low temperatures. Spray the bolt to shrink it
and give it a good go.
If the head is gunky with resins from long use, soak it over a few
days in anti-freeze in a heated crock pot. Do that outdoors and away
from pets just to be safe.
An aside to the idiots here: Don't let's start another MEK debate
over this one, folks. It's just common sense.
Last resort, take it to a machine shop for removal of the bolts.
They've got all the goods needed and on the off chance they break
one or the threads get bunged during the process, they can fix them
on the spot for you.
Ray, I was with you on the MEK but I'm going to have to say that putting an
engine in a vice is a bad idea. I've ruined an engine that way(I was 13
years old). You can distort the crank case(in my experience) or the
cylinder head. That is: Been There Done That advice.
To the OP may I suggest that a constant pressure on the wrench might
help as the goo that holds it might give slowly, like gummy sugar. Also
heat, but even heat, like the whole engine(no carb) in an oven, hold with
pot holder.(safety first) as opposed to spot heat of a torch or heat gun.
On Wed, 3 Oct 2007 23:38:14 -0500, I said, "Pick a card, any card"
and "MJKolodziej" instead
I should have been more clear on that. You don't actually grip the
engine, you just make it tight enough so it can't turn when you
apply pressure to the head bolts. The rag will keep it from
Pot holder or rag, you need something to keep it from spinning out
of your grip while you apply more torque to the bolts. One guy I
know used a short piece of square metal tubing to hold the engine.
I'll second all of that. You can also soak the engine in a jar of fuel
or plain alcohol to loosen the gooey oil. Be sure to get the crud out
of the screw heads to allow the tool to get seated properly on the screw.
Your best bet for loosening the threads is heat.
I might suggest that you use your Dremel cutoff disc to create a 'new'
unrounded end of the Allen wrench before starting, then use a slow steady
Cheers -- Lyman
"On so-called global warming or climate change, let us not scare ourselves
with catastrophic forecasts, or use them to defend and promote irrational
interventions in human lives."
"Ray Haddad" wrote in message
On Thu, 04 Oct 2007 08:51:01 -0400, I said, "Pick a card, any card"
and Ed Cregger instead replied:
Ah, now that's what I like! Turn this into an "X-treme Hobby" in one
grinding, metal chip rendering pass!
On Thu, 4 Oct 2007 16:36:28 -0500, I said, "Pick a card, any card"
and "Six_O'Clock_High" > and
It could be the next reality TV show. RC Flying With the Stars.
Give them weak batteries, dead cells, no frequency flags, bad fuel,
jiggling power switches and stripped servo gears; then let them run
the AMA pattern with only a single day of practice. Do it next to a
skeet range and you have maximum entertainment value.
One way to keep allen head bolts and phillips head screws from slipping is
to dip the wrench or screwdriver into fine auto valve grinding compound
before trying to loosen them. It will increase the "bite" almost
Also, the screws will not be actual "Phillips" type, but "JIS" type screws.
Use the proper tool for the job, and success is much more likely....
I like to use the "cooking an engine in a crockpot full of antifreeze"
overnight. Remove the engine and while it is still warm all the screws
should come out free and clear. Works great if the piston is frozen too.
Been working on engines , auto and model , all my life and never heard
of this one. Thanks for that tip , I will try it.
The bolts are " socket head ", " hex head " , and are also called
"allen head" ....... all the same.
JIS is a standard , Japanese Industrial Standard I believe.
You've gotten a lot of good advice from the other guys , but
ifall else fails , I have used a Dremel tool to cut a "slot"
in the heads for a flat screwdriver. You will cut the head
a bit , but it won't matter as long as you just cut the surface
Generally, a "gentle turn" is just not what's required. You gotta want
Get the right size allen wrench, make sure the engine is cold, not
hot, put the thing in a vise to hold it, and twist the allen wrench,
steadily but firmly with two hands, until either the wrench breaks, or
the bolt comes loose. Don't worry, the wrench won't break. I'd make
sure I was using a good quality wrench, not one of those freebies they
give with a set of screws, or a balldriver, since they have much less
area to bear on the screw, and the go for it. if worse comes to worst,
you can grind off the offending screw heads, pull the head off , and
then take them out with a pair of vise-grips, or just get a new engine...
By the way, why was it that you needed to pull off the head anyway...?
ken day wrote:
It was a small "trial" turn. I think I stripped the glow plug threads
and either want to replace the head, rethread the hole off of the
engine to prevent metal shavings getting into the cylinder or put a
helicoil in the head.
BTW, thanks for all of the advice and guidance to all of you.
In another post, someone objected to putting an engine in a vise.
I have found it necessary to do this on occasion, and I "pad" the engine
from the jaw marring the engine by using blocks of wood. Also, to keep from
distorting the engine, I barely put any squeezing pressure on it, but
instead orient the engine so the lugs or some part of the engine will