head thread repair on aluminum block

On 2 Oct 2006 09:34:47 -0700, wrote:

>OK, so we helicoiled it. Used the suggestions of welding the tap to an
>extension it worked great. 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. Used some zinc assembly lube (all I
>could find). Did a test torque with the old gasket. All of the holes
>are good up to 80 ft lbs but the bolt is jumping around in the helicoil
>hole past 50 lbs. Removed it, and relubed it a few times but no
>improvement. Think moly lube would be better? I'm not sure if it's
>jumping in the helicoil hole because of something we did wrong, or
>because it is steel on steel so it needs different/better lube.

I haven't been following this thread, but I'm going to make some
presumptions:
you are talking about steel and aluminum. The coefficients of thermal
expansion are different, depending on the alloy.

What you want to aim for is a fastener TIGHTENING in a hole as the
assembly heats up. IOW, the fastener should have a larger coefficient
of thermal expansion than the pieces being assembled with that
fastener, to prevent the fastener from loosening in the hole as the
assembly heats up. The hole gets bigger, the fastener better be able
to keep up with it. I suspect in your case...the hole in the aluminum
is getting larger, and the helicoil is -not- expanding along with it
to keep a tight bond. Of course it is expanding somewhat, but it has
to overcome or at least match the rate and dimensions of the expansion
of the assembly metals.

Just a thought from a guy in the peanut gallery, who has come to the
game *late,* and doesn't know "who is on 2nd"

Lg

You could easily be describing the results of trying to put a bolt with
the wrong threads into a helicoil....

Are you 'sure' the book is wrong???

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/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

wrote:
>
> OK, so we helicoiled it. Used the suggestions of welding the tap to an
> extension it worked great. 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. Used some zinc assembly lube (all I
> could find). Did a test torque with the old gasket. All of the holes
> are good up to 80 ft lbs but the bolt is jumping around in the helicoil
> hole past 50 lbs. Removed it, and relubed it a few times but no
> improvement. Think moly lube would be better? I'm not sure if it's
> jumping in the helicoil hole because of something we did wrong, or
> because it is steel on steel so it needs different/better lube.

wrote:
> OK, so we helicoiled it. Used the suggestions of welding the tap to an
> extension it worked great. 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. Used some zinc assembly lube (all I
> could find). Did a test torque with the old gasket. All of the holes
> are good up to 80 ft lbs but the bolt is jumping around in the helicoil
> hole past 50 lbs. Removed it, and relubed it a few times but no
> improvement. Think moly lube would be better? I'm not sure if it's
> jumping in the helicoil hole because of something we did wrong, or
> because it is steel on steel so it needs different/better lube.

Jumping, as in the static friction in the threads is so great that you
turn the bolt-head a little, and the threaded part is 'stuck', then the
threaded part suddenly turns a bit in the threads?

Or jumps, as in you put torque on the bolt head, and the bolt head
doesn't move, then all of a sudden the bolt head turns a bit (large
static friction where the bolt head meets the head).

Or, as Mike R suggests, could the bolt actually be slipping out of the
threads?

Dave

wrote:
> OK, so we helicoiled it. Used the suggestions of welding the tap to an
> extension it worked great. 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. Used some zinc assembly lube (all I
> could find). Did a test torque with the old gasket. All of the holes
> are good up to 80 ft lbs but the bolt is jumping around in the helicoil
> hole past 50 lbs. Removed it, and relubed it a few times but no
> improvement. Think moly lube would be better? I'm not sure if it's
> jumping in the helicoil hole because of something we did wrong, or
> because it is steel on steel so it needs different/better lube.
>
i don't know what the thread is on a prelude, but i can tell you for
sure that the head bolt thread pitch on the civic is 1.25mm - i've just
checked a couple i have in my box of bits.

but since you've already helicoiled the block and are committed at this
point, and have screwed the bolt in, you'll have effectively re-threaded
the bolt. i suggest you screw it in and out a few times to complete the
cutting process, then leave it. you'll know better next time. you may
want to up the torque a couple of notches too. the finer thread with
give a higher bolt tension than the coarser thread at the same torque,
so since you have a coarser thread, the torque needs to be a little
higher to get the bolt tension. not sure exactly how much without
looking it up, but you may be able to find it on the web somewhere.

jim beam wrote:

> i don't know what the thread is on a prelude, but i can tell you for
> sure that the head bolt thread pitch on the civic is 1.25mm - i've just
> checked a couple i have in my box of bits.

That sucks, before ordering the Helicoil stuff we checked the bolt
against a thread gauge at Napa (fit exactly 12mm x 1.5) but I guess
something was wrong since there would be no other reason for the bolt
to be jumping now. I thought if the threads were wrong it would start
hanging up way before that point....

> but since you've already helicoiled the block and are committed at this
> point, and have screwed the bolt in, you'll have effectively re-threaded
> the bolt.

Well, do you think it would be possible to find a 12mmx1.5 bolt to use
in its place? The bolt is 6 3/8 inches and the threaded part is 1
inch. The head is 14mm. I don't know where to look for this kind of
thing... the best I could think of is maybe some other Honda uses a
similar bolt.

> i suggest you screw it in and out a few times to complete the
> cutting process, then leave it. you'll know better next time.

Yeah, we sure will.

> you may want to up the torque a couple of notches too. the finer thread with
> give a higher bolt tension than the coarser thread at the same torque,
> so since you have a coarser thread, the torque needs to be a little
> higher to get the bolt tension. not sure exactly how much without
> looking it up, but you may be able to find it on the web somewhere.

http://www.futek.com/boltcalc.aspx?mode=metric

I put in the following values for the original bolt:
Application Data
Major Bolt Diameter: 12.00
Bolt Pitch: 1.25
Bolt Proof Strength: 827
Recepticle Length: 25.4
Recepticle Strength: 414
Applied Tensile Load: 0
k Factor: 0.2

Recommended Torque
113.25 N-m
(11.555 kg-m)
(83.52 ft-lb)
Resultant Tension:4811
Maximum Torque
151 N-m
(15.407 kg-m)
(111.36 ft-lb)
Resultant Tension:6415

83 ft lbs is in the ballpark of the recommended torque from the manual
(78 ft lbs)

And then the following values for the current situation:

Application Data
Major Bolt Diameter: 12.00
Bolt Pitch: 1.50
Bolt Proof Strength: 827
Recepticle Length: 25.4
Recepticle Strength: 414
Applied Tensile Load: 0
k Factor: 0.2

Recommended Torque
108.19 N-m
(11.039 kg-m)
(79.79 ft-lb)
Resultant Tension:4596
Maximum Torque
144.26 N-m
(14.718 kg-m)
(106.39 ft-lb)
Resultant Tension:6128


What is strange is that it actually recommends less torque for the 1.5
pitch (79 ft lb) than for the 1.25 pitch (83 ft lb) with everything
else constant. That doesn't really make any sense, does it?

wrote:

>
> What is strange is that it actually recommends less torque for the 1.5
> pitch (79 ft lb) than for the 1.25 pitch (83 ft lb) with everything
> else constant. That doesn't really make any sense, does it?

Actually that does make sense, on a coarse thread you have less surface
contact per length of threaded area, so you are losing less of the
torque reading to thread friction.

wrote:
> wrote:
>
>> What is strange is that it actually recommends less torque for the 1.5
>> pitch (79 ft lb) than for the 1.25 pitch (83 ft lb) with everything
>> else constant. That doesn't really make any sense, does it?
>
> Actually that does make sense, on a coarse thread you have less surface
> contact per length of threaded area, so you are losing less of the
> torque reading to thread friction.
>
to be honest, i haven't thought it through. i was under the impression
that finer threads gave higher tension for a given torque based on
geometry. it may be that a lower torque is specified because typically,
coarser threads are in lower strength bolts. i'll think about it some more.

wrote:
> jim beam wrote:
>
>> i don't know what the thread is on a prelude, but i can tell you for
>> sure that the head bolt thread pitch on the civic is 1.25mm - i've just
>> checked a couple i have in my box of bits.
>
> That sucks, before ordering the Helicoil stuff we checked the bolt
> against a thread gauge at Napa (fit exactly 12mm x 1.5) but I guess
> something was wrong since there would be no other reason for the bolt
> to be jumping now. I thought if the threads were wrong it would start
> hanging up way before that point....

well, if you checked the bolt with a thread gauge and it was 1.5mm, then
you got it right! that's good news.

>
>> but since you've already helicoiled the block and are committed at this
>> point, and have screwed the bolt in, you'll have effectively re-threaded
>> the bolt.
>
> Well, do you think it would be possible to find a 12mmx1.5 bolt to use
> in its place? The bolt is 6 3/8 inches and the threaded part is 1
> inch. The head is 14mm. I don't know where to look for this kind of
> thing... the best I could think of is maybe some other Honda uses a
> similar bolt.

best stick with the original bolt regardless.

>
>> i suggest you screw it in and out a few times to complete the
>> cutting process, then leave it. you'll know better next time.
>
> Yeah, we sure will.
>
>> you may want to up the torque a couple of notches too. the finer thread with
>> give a higher bolt tension than the coarser thread at the same torque,
>> so since you have a coarser thread, the torque needs to be a little
>> higher to get the bolt tension. not sure exactly how much without
>> looking it up, but you may be able to find it on the web somewhere.
>
> http://www.futek.com/boltcalc.aspx?mode=metric
>
> I put in the following values for the original bolt:
> Application Data
> Major Bolt Diameter: 12.00
> Bolt Pitch: 1.25
> Bolt Proof Strength: 827
> Recepticle Length: 25.4
> Recepticle Strength: 414
> Applied Tensile Load: 0
> k Factor: 0.2
>
> Recommended Torque
> 113.25 N-m
> (11.555 kg-m)
> (83.52 ft-lb)
> Resultant Tension:4811
> Maximum Torque
> 151 N-m
> (15.407 kg-m)
> (111.36 ft-lb)
> Resultant Tension:6415
>
> 83 ft lbs is in the ballpark of the recommended torque from the manual
> (78 ft lbs)
>
> And then the following values for the current situation:
>
> Application Data
> Major Bolt Diameter: 12.00
> Bolt Pitch: 1.50
> Bolt Proof Strength: 827
> Recepticle Length: 25.4
> Recepticle Strength: 414
> Applied Tensile Load: 0
> k Factor: 0.2
>
> Recommended Torque
> 108.19 N-m
> (11.039 kg-m)
> (79.79 ft-lb)
> Resultant Tension:4596
> Maximum Torque
> 144.26 N-m
> (14.718 kg-m)
> (106.39 ft-lb)
> Resultant Tension:6128
>
>
> What is strange is that it actually recommends less torque for the 1.5
> pitch (79 ft lb) than for the 1.25 pitch (83 ft lb) with everything
> else constant. That doesn't really make any sense, does it?
>

jim beam > wrote in
t:

> wrote:
>> wrote:
>>
>>> What is strange is that it actually recommends less torque for the
>>> 1.5 pitch (79 ft lb) than for the 1.25 pitch (83 ft lb) with
>>> everything else constant. That doesn't really make any sense, does
>>> it?
>>
>> Actually that does make sense, on a coarse thread you have less
>> surface contact per length of threaded area, so you are losing less
>> of the torque reading to thread friction.
>>
> to be honest, i haven't thought it through. i was under the
> impression that finer threads gave higher tension for a given torque
> based on geometry.




Fine threads are used in instances where vibration is a concern.

Consider that, mechanically, a screw thread is just a variation of a
wedge. The shallower the slope of the wedge, the less the mechanical
advantage of the opposing (loosening) force. And, conversely, the easier
they are to strip...



> it may be that a lower torque is specified because
> typically, coarser threads are in lower strength bolts.



Coarse threads are, in and of themselves, stronger, but are more
susceptible to vibration and loosening on account of their steeper
slope. There exist M12 bolts with coarse threads, and indeed, they are
in certain circumstances easier to find than fine-thread fasteners.

Correct stretch and the use of prevailing torque nuts can satisfactorily
allow coarse-thread fasteners to substitute for fine-thread fasteners.


--
TeGGeR®

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/

wrote:
>
> jim beam wrote:
>
> > i don't know what the thread is on a prelude, but i can tell you for
> > sure that the head bolt thread pitch on the civic is 1.25mm - i've just
> > checked a couple i have in my box of bits.
>
> That sucks, before ordering the Helicoil stuff we checked the bolt
> against a thread gauge at Napa (fit exactly 12mm x 1.5)

I guess you now know why the hole was stripped.....

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/pi...?id=2115147590
(More Off Road album links at bottom of the view page)