ehcoplex 

Just took apart, cleaned, lubed and installed a recently acquired set of Cyclone derailleurs (early version). Unilke most of the other derailleurs I've messed around with, there are no tiny springs on the stop screws. I've always assumed these springs are to put some tension on the screws to keep them from turning out of adjustment. Should there be springs on these screws? They do seem pretty easy to turn (I can do it with my fingers- unless it's up against the stop..) and I'm a little concerned they could work their way loose..

sd5782 

Obviously a case of needing a spoke protector too just in case it does go out of adjustment. Sorry, just couldn’t help myself..

TiHabanero

The only der I have had the adjustment screws change adjustment on me is a Shimano Deore rear der. A small amount of blue loctite took care of it. Never has a Suntour der lost limit screw adjustment, and I have ridden a couple of them for 10's of thousands of miles.

steelbikeguy

I don't recall seeing any springs in the many Cyclone's that I've owned.
Here's an example...



I haven't looked lately (and am too lazy to walk over to one of my bikes thusly equipped), but I recall the screw shaft having a V ground in its length. I assumed that was to create a snug fit.
As noted, if there is any concern, a bit of blue threadlock compound should take care of any inclination to wander around.

Steve in Peoria (sometimes I rely on accumulated crud to lock threaded fasteners in place. )

ehcoplex 

Yeah, I meant to note in the OP that the screws have a very fine groove running perpendicular to the threading...

SurferRosa

No.

oneclick 

In which, if you look closely, is fixed a section of some sort of plastic, which acts as the locking-mechanism (hence no springs); on the screw on the right in the picture below you can see how some of it is smeared into the threads adjacent the groove:

Prowler 

^^^^^ +1. I have worked on several Suntour RD and FD and none have had loose adjustment screws. I agree that they have a tiny strip of plastic in a groove to serve as a thread lock. You can see it if you clean the screw and use a magnifying glass. BTW I think the Suntour adjustment screws are a finer thread than either Shimano or Campy screws so don’t loose them. I’m not aware of any substitutes. I never throw away a broken one without salvaging the screws. And spacers and shims and springs and anything else interesting.

ehcoplex 

Hmmm- it seemed like there was just grease/crud in those grooves, and most of it (I think) came off when I deep-cleaned everything. Maybe a tiny bit of blue locktite will serve as a little insurance.

JohnnyRingo

Yup

JohnDThompson 

Yes, SunTour used a nylon insert on those bolts to prevent spontaneous loosening. If the nylon is worn or missing, I'd clean the bolt and threaded hole thoroughly and use a little blue loctite on the bolt. Get the derailleur adjusted before the loctite sets up, otherwise it will be a bit more of a struggle turning the bolt.

Aardwolf

They are 4mm metric fine thread.

I had to drill out and rethread a stripped B screw as 5mm metric fine so I checked all the threads.

sd5782 

I’ve mostly seen the Suntour adjustment bolts being too hard to move vs being too loose. Finger tight doesn’t inspire confidence. Another hobby I have is vintage spring powered pellet guns. Because of the vibration, the stock screws can loosen causing poor accuracy. The common Loctite blue is often recommended, but it “locks” the screw, and doesn’t allow any more adjustment or checking without breaking screws loose.

Years ago , I found another Loctite version in their purple 222 product. It is for small screws under 1/4” and remains gummy, so adjustments and checks can be made. It is never stocked anywhere and needs to be an online purchase. This may be your answer. I bought one of the little bottles, and it has serve me for over a decade. I believe a similar product is “Vibratite” which may be a Permatex product IIRC.

clubman 

I'd try a smidge of plumbers tape...at least it won't set up on you.

C9H13N 

Somewhat on topic, does anyone have a good source for replacement Suntour screws? I’ve had some come through that were boogered on arrival, and frozen in place to boot.

Hardware store stainless is an option, but not my preference.

Aardwolf

You can get stainless allen key versions on Ebay.
I think the head is slightly wider but it works.

https://www.ebay.co.uk/itm/384387662...3ABFBMmqnHwcth

M4 metric fine is 4mm x 0.5mm
M4 metric normal is 4mm x 0.7mm
https://www.engineeringtoolbox.com/m...ads-d_777.html

zandoval 

Ha... I know... Yes, crud can be of some use. It's kinda like this bike I recently saw on the Galveston Sea Wall. The only thing holding it together was the rust...

Also... Here is another use for your Plumbers Thread Compound Stick. You can just keep it in the tool box and don't have to worry about it drying up like Locktight. Smear a little on your threads and they will stay reasonably tight even after a lube.