So if you remove a bolt with threadlock on is it best practice to replace the threadlock with new?
If so do you need to clean off all the old stuff and in that case what about the inside of wherever the bolt screws into?
Finally, if you do replace it/add more on top, how do you tell what strength the original stuff was?
Caveat, IANAE
So if you remove a bolt with threadlock on is it best practice to replace the threadlock with new?
I do
If so do you need to clean off all the old stuff and in that case how do you get the stuff off the inside of wherever the bolt screws into?
I clean it to remove any grease and loose bits
Finally, if you do replace it/add more on top, how do you tell what strength the original stuff was?
I work off the torque setting, size and material of the fastener. Compare this to the breakaway torque in the manufacturer's spec, 6Nm torque setting gets 6Nm breakaway threadlock
EDIT: Breakaway spec varies with the size of the fastener; a larger fastener will have more surface area and will need more torque exerted to breakaway than a smaller one
Some proper info here https://www.loctiteproducts.com/en/know-how/build-things/threadlocker-red-or-blue-which-ones-right-for-you.html
I would. In genral threadlocks cure, the reaction is catalysed by metal so starts when applied. Once removed it's just cured material so won't bond the second time. Based on the formulations I've seen it is pretty comparable to some 2k glues.
That applies to the more permanent ones not sure about the less permanent ones (blue locktite).
What about the ones that come pre loctited by Shimano et al?
depends on the situation and the state of the threadlock on the bolt
if there's a decent amount showing, then its probably fine. simply having some on the thread causing the the threads to bind slightly is usually enough for the application on bikes, which is generally just to prevent the bolts from rattling free
What about the ones that come pre loctited by Shimano et al?
that’s a good point. On those it’s already cured isn’t it?
As above, if the old threadlock still prevents the screw rattling loose it will do for bike situations. If the screw can be turned by my fingertips then a dab of new threadlock goes on. I haven't died yet.
In critical applications a new bolt and cleaning the hole is the way to go. On a bike application it doesn't really matter, especially if you can torque a bolt by feel as long as there's enough present. Pre cured threadlock or patchlock (pre applied) can alter the rundown torque (sometimes for the better) as does fresh stuff, so using a torque wrench can give variation in the preload. I use 243 on most bike applications, and usually just put a tiny bit on when reusing a bolt. If there's still plenty of patchlock on, I'll reuse as is, but I'm feeling for the rundown to make sure there's enough on.
IAAE