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.
I'm saying you're living in a fantasy world where you can simply neglect losses due to dynamic friction, that you have exchanged for whatever mechanical advantage you have gained.
Go to an online torque calculator. Fill out the clamping force and bolt characteristics. Calculate the torque for a fine and coarse thread bolt. Everything else held constant, the apparent torque required to obtain a given clamping force is less for the coarse thread bolt than for the fine thread one (in my case, 77 lb-ft vs 83 lb-ft).
Something tells me the model used by an engineering firm takes a few more empirically obtained factors into account than your Aristotlean model does...
I'm saying you're living in a fantasy world where you can simply neglect losses due to dynamic friction. That isn't the world I live in.
Go to an online torque calculator. Fill out the clamping force and bolt characteristics. Calculate the torque for a fine and coarse thread bolt. Everything else held constant, the apparent torque required to obtain a given clamping force is less for the coarse thread bolt than for the fine thread one (in my case, 77 lb-ft vs 83 lb-ft).
Something tells me the model used by an engineering firm takes a few more real world variables into account than your Aristotlean model does...
It doesn't spin out, like I said, it jumps around. The problem is that I think it is next to impossible to get accurate torque when that is happening. What do you think?
I really have two options. Either it jumps and afterwards the pointer lands on 80, or it jumps only after I have applied enough force to put the pointer at 80. Which do you think is closer to where it needs to be? I am thinking it is the latter.
So, you ADMIT there is a gain in mechanical advantage, by using a fine thread over a coarse thread. Thank you very much. You can go back to your nap now.
Have you tried putting a washer under the bolt head, or lubricating the area where the bolt contacts the cylinder head? It could be that the bottom of the bolt head is just sticking to the aluminum of the cylinder head.
I would do as Earle mentions and use a washer then bring it up as close to 80 as I could on break away torque trying to be as smooth as possible.
You also should be aware that a lubricated torque is 'way' lower than a dry torque right? The fifty or 60 ft lb lubed up might be the same as your head calls for if it is the normal dry torque readings.
Mike
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does it tighten smooth to a given torque then start jumping? if so, you can count the turns [and fractions thereof] on an ok bolt from that torque to the required torque, then repeat the same number of turns on the problem bolt. that should get you close enough.
So tell me again how this new discovery refutes my earlier post that you jumped all over? The results from the torque calculator show that the whole thing cannot simply be dismissed in the two words "mechanical advantage".
I don't know how you got into this situation, and I don't know how you're going to get out of it.
IIRC, you said the specs given by the manual/book were wrong, as you had a "WTF moment," and you went ahead with a procedure that contradicted the manual's instructions, if I interpret this all correctly. Now you're complaining that the bolt isn't holding like it should.
I can't see your aluminum block, I can't see the hardware in question, I have no further comment, other than it appears you're in over your head, and it might be a good time to call in someone who knows what they're doing.
No, you interpret wrong. The bolt is holding. What the bolt is not doing is turning smoothly. That is a problem because the carefully calculated correlation between apparent torque and clamping force then dissolves.
The bolt that came out was checked against a gauge. It was determined to be a 1.5. The book says 1.25. Ergo, the book is wrong. If the book is right, then the NAPA bolt gauge is wrong (and by wrong, I mean not even in the ballpark, and it's STILL wrong after a recheck).
When "the book" is wrong, that's an automatic WTF moment, no?
I'll dearly miss your comments, you know.
The people who "know what they're doing" wouldn't even touch the helicoil job. That's because they want to stay in business and they can't stay in business doing repairs they can't guarantee. Helicoiling one hole in the block and assuming the others won't pull out in the same fashion that one did is not a repair they can guarantee. However, it's a risk we can live with.
I'm now back to about 30 posts ago.
We installed the correct helicoil using the correct procedure (drill, tap, etc).
The bolt is now jumpy when torquing it.
I thought it was a lube problem, because that's what it acted like. The respondents all thought it was a thread problem. But thread problems just don't act like lube problems. We are absolutely certain now that we measured the threads correctly and used the correct helicoil.
The best idea I now have to approximate the original clamping force is to count turns from the torque where the bolt starts to jump to the final torque, using a reference bolt that doesn't jump. From jim beam's post.
If nobody else has a better suggestion, that's what we'll go with. If the Honda motor becomes a steam engine, so be it. Can't win them all.
Here is what I would do - replace the bolt with a stud. Either buy a pre-made stud of the correct lenght or make one. Use loctite stud and bearing mount on the threaded portion that screws into the block. I'd screw it in as tight as I could with the stud and bearing mount applied (but not so tight that it "jumps"). I'd then I'd install a nut on the portion of the stud that extends from the head. I'll bet I would have no problem torquing the nut to the correct value.
Here is what I would do - replace the bolt with a stud. Either buy a pre-made stud of the correct lenght or make one. Use loctite stud and bearing mount on the threaded portion that screws into the block. I'd screw it in as tight as I could with the stud and bearing mount applied (but not so tight that it "jumps"). I'd then I'd install a nut on the portion of the stud that extends from the head. I'll bet I would have no problem torquing the nut to the correct value.
"C.E. White" has what appears to be a solution to the problem. Sounds good to me. I would give it a try. I think the hard part would be finding a stud of the correct diameter and tensile strength. Other than that, I would give it a go. Like you say, what's to lose at this point?
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