head thread repair on aluminum block

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...

Are you this pretentious in real life?

 

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...

Are you this pretentious in real life?

 

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.

Lg

 

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.

Earle

 

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
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)

 

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.

 

It has a washer from the factory. We lubed both sides of the washer
too.

 

It calls for 26/52/78 with engine oil lube.

 

Yes, that's exactly what it does.

Your suggestion makes the most sense yet. I'll have a chance to look
at it this weekend and that's what we will go with.

 

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".

 

You apparently are having a problem with a bolt.

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.

Lg

 

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.

Ed

 

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.

Ed

 

Sounds like an excellent suggestion, Ed.

 

"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?

Lg