Is it possible that the bolt really was a 1.25 but was able to thread into the 1.5 gauge anyway? Of course, maybe their gauge was cross threaded by another customer.
So what can be done about it jumping around? It'd be nice to get something approximating the correct torque on it.
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.
"Earle Horton" wrote
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
Yeah, it's more a problem that the damage is already done and now what?
Yes.
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
wrote
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.
What about a "big-sert?"
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.
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
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
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