Carbocation

I just bought a classic Cinelli quill stem that looks just like first stem on this page: https://www.bikepro.com/products/stems/cinelli-road.html

I noticed that the expander bolt is a bit stripped out and would like to replace it. According to that site:
"The expander bolt is made of chrome plated steel, with 7mm x 1mm pitched threads, a 135mm length"

I found something close, a hex key "Socket Cap Screw" on https://www.mcmaster.com/ :

Part Number: 91292A425

Stainless Steel Type
18-8 Stainless Steel

Drive Style
Hex Socket

System of Measurement
Metric

Thread Size
M6

Metric Thread Pitch
1 mm

Length
140 mm

Hex Key Size
5 mm

Thread Style
Right Handed

Thread Length
Partially Threaded

Head Diameter
10 mm

Head Height
6 mm


Would this work? If not, where can I find one that does?

sch

That is probably the closest you will get to the right bolt for an antique stem like that. (I have one on my 'vintage' Teledyne Titan, it is way too fine to replace.) You will then need to get a new expander nut threaded for the M6x1 thread.
M7x1 is an oddball threading and the original is the only 7mm socket head screw I have ever found. Most metric allen sets skip the 7mm size for that reason. Another option would be to braze an M6x1 nut on the bottom of the expander cylindrical nut, sounds like you have the length to do this. The M6 nut would have to be attached to the cylindrical expander or you would not be able to loosen the expander, which is done by unscrewing the SHCS a few turns and tapping it with a soft headed hammer.
Steve

classic1

I got my last one here.

https://www.parker-international.co.uk/

It was 2 or 3 years ago, but you never know your luck.

caotropheus

I do not know if you really need an exactly bolt and nut for the stem. Go to a shop, not any shop, but a shop that is open already for a couple of decades, take the stem, including the bolt and the nut for sure they have at least a box full of bolts and nuts similar or equal to what you are looking for.

classic1

+1

HillRider

As sch said, M7x1.0 threading is extremely odd-ball and you are unlikely to find it anywhere. The M6x1.0 bolt you found is not going to fit the current expander but, if the project is worth while to you, you could have it Helicoiled to M6x1.0 threads.

BTW, M6x1.0 isn't that common either as M6x1.25 is the more common threading. If you are going to have the expander rethreaded, you might as well go for that thread configuration.

Carbocation

Alright, so I've been to a few bike shops (Ye Olde Bike Shoppe and Pedal Pushing), but they didn't have any matches. They told me that the Cinelli style expander is kind of rare (it looks like a Rolo caramel, or a tapered squat cylinder), versus the more common wedge-type.

I feel kind of iffy about brazing a nut to the bottom of the expander - what if it snaps off when I'm torquing the stem in? How would I get the stem out?

I think retapping the threads sounds like the best idea. Where can I go to get this done? Auto shop? Home Depot?

HillRider

Try a machine shop.

sch

For a machine shop, it would probably be easier to just chunk in a length of bar, turn it to match the contour on the expander nut and drill and tap to your bolt. Less trouble than finding a metric helicoil
set up. You might measure the recess size and bolt hole size and see if the M8 bolt might fit. There is a table on top of the page in the McMaster website that gives the M8 headsize as 13mm diameter. Probably to big for the stem but if it fits, it would be easier to just drill the 7mm hole threads out and retap. The
brazed M6 nut would likely be safe to use assuming you don't whale away at the stem bolt in removing. In my experience it doesn't take much of a tap to knock the expander out. You can always unscrew the bolt and insert a 6mm steel rod a little off center as a punch to knock the expander out. It would not come loose in compression, but might be knocked off when loosening for removal of the stem, not likely IMO.
Steve

shaq-d

what does it matter what's at the bottom? u can unscrew the wedge and put in the rolo.

sd

Carbocation

sch: Thanks for all the good info. Now I'm off to the yellow pages to find a machine shop.

shaq-d: I wrote in response to caotropheus & classic1, who told me to salvage a bolt+nut from another stem. All I could find were the wedge types. The wedge and rolo types are completely incompatible with each other.

jimmythefly

Carbocation -I have one of those stems. Check your PM.

sch

You may be stunned at the prices asked for such a simple piece of work at a commercial machine shop
if they will even talk to you. For an alternative you might approach the faculty at a place like
https://www.city.sdccd.cc.ca.us/voced/pages/MACT2.htm where they might be amenable to doing this as a student project. The materials cost would be minimal and it could probably done in less than an
hour, assuming they have the right tap. Someone familiar with a lathe could probably do it in 20min.
You apparently have a private email from fly that may help. One other thing, McMaster is easy to deal with but shipping will cost 5-10x the cost of the item unless you work somewhere that will let you piggyback onto another order or have other stuff to order (such as the tap and drill bit you might need.)
My last order to them arrived in 2days. Alternatively, there is no reason why an English threaded bolt couldn't be used, if the expander has to be replaced or drilled out and retapped anyway. Cost for a similar sized bolt should be same or close.
Expander type stems were dodoed out by the wedge types early on when manufacturing shifted to Japanese and Chinese (Taiwan then) sources from European stems where expander was standard. The wedge type bends the mounting bolt as torque increases as the wedge is off center.
Steve

Carbocation

jimmythefly - I sent you a PM. Thanks.

shaq-d

i'm still not getting this. you're telling me the BOLT for wedge and rolo types are completely incompatible? you couldn't find one bolt that would fit your current one? i find it really hard to beileve..(?)

sd

Carbocation

Yeah, the wedge-type bolt was visually wider in diameter, and had more widely-spaced threads. The Cinelli type was skinnier and had more closely spaced threads. It's not that surprising, given the bicycle industry's history of making incompatible standards (eg. bottom bracket threading, handlebar clamp diameter, freewheel threading, cassette spacing, etc.).