Helicoil Experiment

 

Here's a little something for those of you that have had to use a helicoil
and have wondered if it will hold, so grab a round of drinks while I explain
how Bep and I spent the weekend.

The idea is to take a 1/2" thick piece of aluminum that Bep cast out of old
lawn chairs and ladders and thread holes that will take a 1/4" 20 bolt.
Most engine cases will use a bigger bolt, but we wanted to keep the torque
lower rather than have to muscle a 1/2" bolt until the threads fail.  Bep
had pre-drilled holes in the aluminum before the experiment.

http://tinyurl.com/5mwqxl

We used a couple of clamps to secure the aluminum to the bench, with a
couple pieces of wood to keep it off the bench.

http://tinyurl.com/68pr7y

We had a couple options to use, but ended up going with the actual Helicoil
brand.

http://tinyurl.com/62n7dn

The first step was to drill out the pilot hole with a #7 drill bit, then tap
it with a 1/4" 20 tap.

http://tinyurl.com/6cz5o9
http://tinyurl.com/6q8ec8

We threaded the 1/4" bolt to make sure the threads were good.  This is a
grade 8 bolt with a rated for 4 ftlbs, which isn't much.

Here's how it looked for the actual test:

http://tinyurl.com/6klb3d
http://tinyurl.com/5da2nl

Time to run the experiment, put the torque wrench on and see at what rating
it pulls the threads:

http://tinyurl.com/6xsfm3

Bep making sure he watches the needle on the torque wrench, nice cut on his
knuckle, that wasn't a result of this experiment.

http://tinyurl.com/6zykl8

As experimentations will often do, we had an unexpected result when at
20ftlbs the bilt snapped.  The threads were still in tact but the bolt was
snapped pretty close to the surface of the aluminum block.  We shouldn't
have been surprised since the bolts are only rated for 4ftlbs.

http://tinyurl.com/5bs6wo
http://tinyurl.com/6g3b9t

We tried this again with the same result, only this time we got to 23ftlbs
before the bolt snapped.  Our conclusion at this point was that the the 1/2"
of aluminum threads were too strong for the 1/4" 20 bolts we were using.
Not to be deterred, we took a few minutes to think of what to do and decided
to drill into the aluminum block with a flat bottomed bit to about 1/4",
essentially cutting the number of threads in half.

We picked a couple new holes in the block and started over, this time we
actually got some numbers that we could use.  With the bolts going into the
bare aluminum threads we stripped the threads at 15ftlbs, 17ftlbs, 17ftlbs,
and 19 ftlbs.  With the same holes, only drilled out and set with helicoils:

http://tinyurl.com/5u6e7c
http://tinyurl.com/5kqdkm
http://tinyurl.com/6rje7y
http://tinyurl.com/6cpmw9

This time with the helicoils in we got thread failure at 15ftlbs, 25ftlbs
(broken bolt, no thread failure), 23 ftlbs and 27ftlbs.  Here's a couple
shot of a failure with the helicoils:

http://tinyurl.com/5cfyer
http://tinyurl.com/588epe

Snapped bolt with helicoil at 25ftlbs:

http://tinyurl.com/6qrqps

So, with 4 successful attempts, it appears the the helicoils are as strong
as or stronger than just the bare aluminum threads.  This is by no means a
definitive test, but it certainly makes me more confident in using helicoils
for engine case repairs.

If you made it this far then help yourself to another beer, we managed to go
through a few during testing

--
Tud
SENS BS#111 LFS#32 FLF MISFIT Vermort AH#115
http://ah115.com
Sisyphus rides a Triumph

 


Hey I'm all for not having an excuse to drink, but that sure looked like a
lot of work when all ya had to do was ask.
BTW, your little experiment was perfect (or close to it) for checking to see
if the bolt would strip out the helicoil or aluminum, but you may want to
consider a tension test.  Instead of using a screw, use an eye-bolt and
check to see how much pull force it will take.  I'm betting the aluminum
casting will fail first.

--
hawgeye ©
www.stealer-dealer.com
 

 


"Tud"


Of course they are - the aluminum is no longer taking the load on a 1/4"
thread, but on the outer diameter of the helicoil - about a 60% bigger area.

Bob

 


<snippage happens>


Glad you got a satisfactory result.  But, you just learnt that
helicoils are at-least, and usually stronger than, the threads they
replace?  Nice of you to go through all that, but helicoils are, by
design, at least a full-size larger thread than the stripped one
they're replacing, simply covering more area in the subject piece, so,
being the quality steel that they're made from, they are inherently
stronger just bytheir increased volume, than the hole-thru-raw-
aluminum they're replacing.

//Ancient History mode ON// Way, way back, (1969) Eye bought  '68
Kawasaki 250 Samurai, as a used bike. It was a hot number, and I
commuted 50 miles each way, sometimes daily, back-and-forth from my
folks home is South Jersey to Fort Dix, where I was just back from a
certain former French colony in Asia, which shall remain
nameless.
  The "dealer" and I use the term loosely, he being a hole-in-the-wall-
garage-with-a-franchise in the early days of Japanese invasion, had
repaired the bike after either he or the first owner stripped out a
cylinder base stud (threads on both ends) by, get this: by drilling a
hole sideways through the threads in the end of the stud, and one hole
from the cylinder hole through the case where stud went through, and
inserting a piece of broken piston ring through the stud, "anchoring"
it thereby, into the case.  He put it back together, managed to torque
the 2-stroke's head down reasonably well, and sold it as a "used bike"
to Yours Truly Dumbass  (me).
  I actshully got pretty good service from this jury rigged mess for
over 6 months.  The bike would run 95 mph, and it did on many
occasions (this is the young, dumb and immortal stage for me,
remember,all nineteen years of me).  I sold it to my friend, who later
became an accomplished road racer and a Kawasaki dealer himself, and
in prepping the motor for racing, he found this cobbled up mess inside
the case and properly helicoiled it, which is what should have been
done in the first place, of course. And, he described to me what he'd
found in the hot little two-stroke engine.
   I guess drilling it through and anchoring a cylinder stud with a
piece of piston ring is what was practice before the invention of
helicoils(?) It worked, but I wouldn't recommend it.  I've used a
number of helicoils in the intervening decades, and never regretted
one. Helicoils are Boss!

--Sarge, Fla. BS109
helicoiled 37UL/37LEC
41U
36EL

 

Tud wrote:

Don't hesitate to use properly installed Helicoils. I've used several on
my engine, haven't had a failure yet.

Chances are the lower numbers you got were due to the bolts bottoming
out. It doesn't take much once that happens.

Les