Lakerat

Derailleur stop screws have some method of maintaining their position once adjusted. What type of retention feature prevents turning during operation? The reason I ask beyond curiosity, is I have a frozen screw and wonder if I'll damage the retention system if I apply heat to free it up. Thanks

headasunder

What type/make era derailleur most of my stock the limit screws thread through a thickish piece of plastic so heat would be out other ones thread into metal and I suspect they all rely on just a snug fit to stay put i have never had one back out but have had the odd one on old beaters that are stuck from neglect.

Andrew R Stewart 

Typical screw rotational controls are a spring providing a load in one direction or a plastic insert which has high friction on the screw. These methods are very common in the rest of industry and the bike world. As limit screws don't usually rotate during the riding any water/salt that gets on them will accelerate any corrosion with no periodic breaking free of said corrosion.

If heat is applied and the plastic (Nylok in other applications) method is at play it will likely melt before enough material expansion is done to free up the screws. Not to mention the other aspects of a der that uses plastics (like cage or hanger pivots bushings) that can be damaged. If a spring is the method that the above still can be in play.

Of course the real solution is avoidance. Lube all screws, keep salt away, move all threaded fittings periodically to insure working ability. One of my pet issues is the claim to never touch the limit screws after initial adjustment. This sets up some (who ride in weather or third/fourth seasons) to end up with frozen limit screws. Of course the trick is to move said hardware a bit periodically then back to what is the correct position. Andy

dsbrantjr

My go-to solution for seized hardware is Kano Kroil; PB Blaster is second best. Plain WD-40 is little better than water IMO.

bulldog1935

the loaded side at its limit is always difficult to turn (and probably shouldn't do it).
Best to move the derailleur off the limit, adjust the screw, and move the derailleur back to check.

If it's oxidation sticking the screw, spray a little boeshield on it and come back in a day.

NJgreyhead

+1

Lakerat

This is a front Campagnol Daytona triple. It had springs for screw retention. Penetrating oil didn't do it, I had to remove it, take it apart and apply heat with a propane torch. Working well now.


The chain line of a used custom made bike was wrong and I had to replace the BB to move the chain line from 51MM to 46MM. The installed BB was a Shimano 115 JIS, I replaced with a 111MM ISO Campagnolo Cenaur BB. So the shorter BB and the change from JIS to ISO moved the chain line where it needed to be. The 111MM BB was specified for triple 9 speed for normal size tubes by Campy.