head thread repair on aluminum block

I would bet money the pitch is 1.25. The online factory
service manual for this Accord says in two places it's a
1.25 pitch bolt. Plus, only one piece of evidence you have
(your own measurement of the bolt pitch) suggests it's not
1.25. "Believe your indications." -- Rule from navy nuke
program when analyzing problems with the plant.
(Psychological studies show a basis for resisting believing
one's indications. One has to 'resist the resistance,' blah
blah when making electro-mechanical diagnoses.)

Yup. Plus all that soft metal will rework itself without
much difficulty, but not to the point where I would trust
the holding power of the setup.

Re-helicoil? I have never done a helicoil job, so I ask for
my own edification as much as yours. The net's reports on
the use of helicoil inserts to repair stripped threads
certainly are promising.

I would be checking the other, so far relatively untouched
head bolts to see that they are 1.25 mm pitch. Get yourself
to a True Value hardware or other store that has a bin of
M12x1.25 etc. nuts, and confirm the pitch?

Isn't "correct torque" rather tangential to the main
concern, namely, how tight the head is held onto the engine?
I personally would not focus on "correct torque" prior to
getting the factory specified male and female threads into
good repair.

Just an amateur here.

 

That resistance thing is called "denial" in civilian psychology courses, and
it is probably the most powerful force known to humans. You are quite right
that "how tight the head is held onto the engine" depends on the thread
pitch. Finer threads have more leverage, and therefore give you more
tightness for the same torque.

Earle

 

I suspect there's more going on here, like the OP is working
in an independent or dealer shop (nothing wrong with either,
of course); has given a quote to the customer; so the budget
is a bit tight; and can't a proper helicoil kit run some
serious change? I was googling on the costs of kits and am
not clear on that.

Seems like these poor folks have found themselves in a
morass here. I am interested in the outcome but fear someone
is going to end up paying through the nose. OTOH, next time
I bet this is a piece of cake.

Probably too often discussion of the phenomenon is applied
to "emotions" (e.g. denying that Jane could have messed over
Paul by sleeping with Paul's best friend yada). Fact is the
technically inclined have to remember it applies to cold
hard science, too.

 

There is a product out there that is used on Nuclear subs, and industrial
equipment that will fix this problem if you can get to it. I've used it,
sold it, and gave it to others. One time I fixed a Cummins diesel head crack
with it, and it's still running.....

I'ts expensive, and I haven't seen any around in awhile. Google for Belzona
products. It's possible someone will give you the little that you need.

MM^^

 

Nope, just a backyard job that fell apart midstream (and had several
cooks in the kitchen who I'm collectively speaking for). The helicoil
kit cost $60 from Amazon.

In the end, the worst case is drop in a used motor.

I hope there won't be a next time <G>

 

Yeah, it's more a problem that the damage is already done and now what?

If anyone has any suggestions on how to do that, I'm all ears.

 

That makes no sense. If anything finer threads would lose more of the
torque value to friction, the same friction that prevents a finer
thread bolt from backing out under the same vibration that would back
out a coarse thread bolt. So in the end you need a higher torque value
to deliver the same clamping force.

 

Not so.
It is called Mechanical Advantage.

With fine thread, you need 20 turns of wrench to say sink fastener 2
inches.

With coarse thread, maybe 10 turns of wrench to sink fastener 2
inches.

So you have a virtual 2 to 1 gear ratio with a fine thread in this
example, and a 1:1 gear ratio with the coarse thread.

Use your head. If you put the same torque on the fine thread that you
put on the coarse thread, you will get TWO times the clamping force,
friction losses notwithstanding.

A mind is a terrible thing to waste.

Lg

 

Great on all points. (I mean, better than having a customer
breathing down your neck!) If you are feeling wealthy
enough, I hope you'll confirm the 1.25 pitch size, buy
another kit (Ebay?), and see how that works. Er, maybe wait
until others who have done helicoil jobs chime in on how
successful a "re-do" is first, though.

Thanks for the update. I am sure someone down the line is
going to learn from this. There really aren't too many
reports of helicoil jobs on head bolt threads for the Honda
newsgroups.

 

I'm getting back to this thread late, but want to agree with the people
who proposed that your head bolts are actually 12mm X 1.25mm pitch.
You'll be hard pressed to find a 12mm X 1.5mm bolt on any (real) Honda
product. That excludes the Passport, etc.

At this point I think the engine is probably beyond saving, unless
there is a double-oversized helicoil product out there I'm not aware
of. It's too late now, but the answer to your "what size Helicoil tap"
question is -- 2mm larger than the intended bolt size in the same
pitch. i.e. repairing a 12mm X 1.25mm hole would require a 14mm X
1.25mm tap (and appropriate drill size). The Helicoil taps don't have
their actual measurments listed on them, but I have measured and
matched all of the common sized metric Helicoil taps to regular tool
taps. Furthermore I have used standard taps in place of the Helicoil
tool with total success.

Toyota MDT in MO

 

i've not seen "double-oversize" options for helicoil. i think the op is
best sticking with the original bolt and multiple re-insertions to get
it as smooth as possible. using another bolt may have very different
elasticity and fatigue properties. [fatigue may be compromised in this
situation, but you gotta suck it and see.]

 

your threads are now as good as you're going to get them. there are no
more "what if's" available to you. run with what you have.

 

for stress analysis purposes, loaded bolts only hold on the first 3
threads* regardless of thread depth/count, so friction on the non-loaded
threads is minimal and can be ignored.

* that may seem counter-intuitive, but it's true. tapered threads can
have higher counts, but they're not practical for common fasteners.

 

What about a "big-sert?"

http://www.timesert.com/html/bigsert.html

They don't list a 12x1.25 big-sert, but it's worth an email.

nate

 

There's always titanium putty and re-tapping to original size...

JT

 

Then perhaps you can tell me why the online torque calculators disagree
with that assessment.

Thanks, but you really have no idea what I do with my mind aside from
my posts in this NG, so you can free yourself from feeling such pity
for me.

 

http://www.timesert.com/html/honda.html
I forgot to mention, another reason I went with the 12x1.5 is because I
emailed Timesert and they recommended the Odyssey kit. The problem is
that the kit costs $400. Just not practical unless you're a pro. But
then that exchange didn't contradict the idea that it was a 12x1.5
either.

 

Ok, so does the damn bolt spin out or just grab a bit when going in?

If it is just jumpy, run with it until the last jump is close to the
torque you want.

If it spins out, you are screwed unless you can tap the hole and drill
the rest out to fit a larger bolt.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)

 

Are you saying, that there is no mechanical advantage of a 20 thread
per inch bolt over a 10 thread per inch bolt? That if 10 ft lbs of
force is used to rotate them, that the clamping force will be exactly
the same, although twice as many turns went into the 20 thread per
inch bolt compared to the 10 thread per inch bolt?

a screw is a gear. specifically, a *ball screw* is a gear, of the
linear kind. It isn't different in how it works than a circular gear,
in terms of mechanical advantage.

I contend, that if I have a 2 to 1 thread advantage...with the same
torque applied via a torque wrench, the fine thread will give more
clamping power than the coarse thread.

If I had a 1 thread per inch screw
and a 10 thread per inch screw
and a 20 thread per inch screw

which one would give more clamping power, revolutions notwithstanding,
with 10 ft lbs of torque applied to the screw head?

You fill in the answer, and show me why you come to your conclusions:



Take all the white space you want/need.

Lg

 

Lawrence,

There is no point in arguing with this type. "Then noticed the Honda
factory book said the bolts were 12mm x1.25 not x1.5. had a WTF
moment but then determined that the book is wrong." The "book
was wrong" because it did not agree with the heli-coil that he had
just installed! And later, "All of the holes are good up to 80 ft lbs
but the bolt is jumping around in the helicoil hole past 50 lbs." So far,
no one reading this thread knows what "jumping around in the helicoil
hole" means. It's obvious too that a coarse thread will provide more
"clamping power", because the threads are bigger!

I would have loc-tited the heli-coil in the hole, after test-threading it
onto the head bolt. You can't be too careful.

Cheers,

Earle