HeliCoil for ErgoStem

I've got a Look ErgoStem Ahead handlebar stem with a stripped lower steerer-clamp thread. It's
definitely the (aluminium) female thread in the stem that's gone, not the bolt. Assuming I can't get
it waranteed...........

If a HeliCoil insert/kit would be appropriate to fix it, what type/size/thread is required?

Would it be advisable to do the other thread too in case that's in danger of failing?

Any details or alternative fixes or comments would be appreciated. As you can imagine, I'm gutted
because this is an expensive stem (it's the funny adjustable one*). Over-tightening is the obvious
cause but it didn't seem like I was torquing that much (with 5mm allen wrench).

* http://www.lookcycle.com/english/catalogue/2003/accessoires.htm

~PB

 

>From: "Pete Biggs"

>If a HeliCoil insert/kit would be appropriate to fix it, what type/size/thread
is required?

Can't help you with the size. Go to the nut/bolt section of any hardware store and screw your bolt
into metric nuts until you find the correct size. Buy two of the nuts. To make the repair you will
need the insert (either a HeliCoil screw locking or a Re-Nu type 303) sized for your bolt, a tap
drill sized for the insert and, for aluminum, two thread forming (better) rather than thread
cutting, taps. The first tap will be a plug tap to start the threads; the second a bottoming tap to
thread to near the bottom of the blind hole. With the tap drill, drill to a depth 1 or 2 threads
deeper than the length of the insert. If you think the shoulder of the stem is not thick enough to
allow this and the tap drill may break through, then drill enough to allow at least 3, preferrably
4, of the threads of the insert and cut the insert to that length with a cutoff disk on a
Dremel-like tool. This is easier to do with the HeliCoil because it is merely a spiral wound wire.
The Re-Nu insert is a solid piece. If you have enough shoulder for a blind hole then tap with the
taper tap followed by the bottoming tap. Or you can drill the hole completely through if the neck of
the stem tapers down considerably from the shoulder. Not a great disaster since the stripped hole is
a the bottom of the stem. If you decide to drill through, all you will need then to cut the threads
is a taper tap which starts easier and requires less torque. To insert the insert, thread the two
metric nuts and the insert onto the bolt so that the insert is at the end of the bolt and tighten
the rear nut against the front. Screw the insert in and back out the bolt and you're done. HeliCoil
inserts have a tang on one end to allow their insertion tool to be used and also requires their tang
break-off tool to remove it. Both are expensive and you don't need them. Merely screw the insert in
tang first into the blind hole if you have enough depth or cut it off. Re-Nu inserts do not require
special tools. Ideally, a small chamfer should be cut around the hole with a standard countersink
tool before tapping to allow the tap to start straight. Liberally coat the taper/plug tap with an
aluminum cutting fluid and start the tap. Be certain it is SQUARE (parallel) to the axis of the
hole. Push and turn. After the first 2 or 3 complete revolutions, back out a quarter turn to break
the chips. Thereafter, a quarter turn back for every complete turn in. Back out completely any time
you feel heavy resistance and clear the chips. Follow with the bottoming tap to 3/4 depth and remove
to clear chips before finishing. Be careful to avoid side pressure on the tap which will cause it to
break in the hole. Practise on a scrap piece of aluminim first if you can.

>Any details or alternative fixes or comments would be appreciated.

Hope that covers it and I didn't leave anything out. Or take the stem and bolt to a machine shop. Or
to your LBS if they're properly equipped, but don't let anyone with pimples perform the operation.

Sig Chicago

 

"Pete Biggs" <pLime{remove_fruit}@biggs.tc> wrote in message
news:[email protected]...
> I've got a Look ErgoStem Ahead handlebar stem with a stripped lower steerer-clamp thread. It's
> definitely the (aluminium) female thread in the stem that's gone, not the bolt. Assuming I can't
> get it waranteed...........
>
> If a HeliCoil insert/kit would be appropriate to fix it, what type/size/thread is required?
>
> Would it be advisable to do the other thread too in case that's in danger of failing?
>
> Any details or alternative fixes or comments would be appreciated. As you can imagine, I'm gutted
> because this is an expensive stem (it's the funny adjustable one*). Over-tightening is the obvious
> cause but it didn't seem like I was torquing that much (with 5mm allen wrench).
>
> * http://www.lookcycle.com/english/catalogue/2003/accessoires.htm

Yes that's a reasonable thing to do. However, since it's blind hole you might want to have it done
by someone ( an LBS, machine shop/engine builder) who's got a few of these behind him/her.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

Pete Biggs <pLime{remove_fruit}@biggs.tc> wrote in message
news:[email protected]...
> I've got a Look ErgoStem Ahead handlebar stem with a stripped lower steerer-clamp thread. It's
> definitely the (aluminium) female thread in the stem that's gone, not the bolt. Assuming I can't
> get it waranteed...........
>
> If a HeliCoil insert/kit would be appropriate to fix it, what type/size/thread is required?
>
> Would it be advisable to do the other thread too in case that's in danger of failing?
>
> Any details or alternative fixes or comments would be appreciated. As you can imagine, I'm gutted
> because this is an expensive stem (it's the funny adjustable one*). Over-tightening is the obvious
> cause but it didn't seem like I was torquing that much (with 5mm allen wrench).
>
> * http://www.lookcycle.com/english/catalogue/2003/accessoires.htm
>
> ~PB
>

Unfortunately, I don't think ergostems are that well engineered - they seem to require excessive
tightening on both pivot bolts to prevent the bars/whole assembly from slipping (obviously you have
to do both pivot bolts a bit at a time, together). I bought one second hand and wondered why one
pivot had a different bolt to the other. Turns out the previous owner had stripped the thread and
tapped a new one. That lasted 5 minutes before it got stripped again. In the end, I drilled out
(vaguely) hexagonal holes in the threaded side of the ergostem, pressed some stainless steel nuts
into the holes and used stainless steel bolts. No problems yet. It doesn't look untidy but obviously
not as good as original. But then the stem only cost me 15 GBP ;o)

I know this doesn't particularly help, but it shows you have to be careful with Ergostem threads as
they aren't that great (for the torque they seem to have to withstand)... if they advise on torque,
probably best to use a torque wrench, then claiming on warranty wouldn't be a problem.

 

RandomChris wrote:
> Unfortunately, I don't think ergostems are that well engineered - they seem to require excessive
> tightening on both pivot bolts to prevent the bars/whole assembly from slipping (obviously you
> have to do both pivot bolts a bit at a time, together).

I haven't had any problems with the pivot bolts - they seem good to me. I think the trick is to
always set it up so the washer notches are engaged, not set inbetween notches (which might squash
them flat). This can be done fine finely tightening bolts until the biting point is just felt, then
adjusting position, then fully tightening; and making sure they're tightened evenly. Some users
might like finer adjustment, but the notches still allow smaller changes than could be got from
changing from one conventional stem to another or re-arranging spacers.

However, I have found the bar clamp bolt needs to be exceptionally tight to prevent slippage, but
this might partly be because my bars are 25.8 and this stem is supposed to be for 26.0. Shame Look
didn't incorporate a front opening clamp.

thanks ~PB

 

A Muzi wrote:

> Yes that's a reasonable thing to do. However, since it's blind hole you might want to have it done
> by someone ( an LBS, machine shop/engine builder) who's got a few of these behind him/her.

...probably will. Thanks.

And thanks very much Sig for the detailed instructions (which I'll keep forever!). I didn't realise
it was that involved. I'm bound to have a go something one day though - but probably on a less
critical/expensive component if I'm doing it all myself.

~PB

 

> I haven't had any problems with the pivot bolts - they seem good to me. I think the trick is to
> always set it up so the washer notches are engaged, not set inbetween notches (which might squash
> them flat). This can be done fine finely tightening bolts until the biting point is just felt,
> then adjusting position, then fully tightening; and making sure they're tightened evenly.

I think this is a good point! My stem would always slip after a few miles and would then be loose
'between' a couple of notches but not go any further. I must have been setting it inbetween the
notches - thanks!

Chris