Loctite minefield

Having trawled previous posts, I remain unsure of the appropriate Loctite (or equivalent) to lock threads on my steam loco. I have recently removed the horn blocks that had been fixed with countersunk bolts and nuts. The previous owner had machined the hornblocks poorly and they needed replacing. I can see the advantage of not using rivets as I would have a problem removing the existing ones.

I would appreciate advice on which Loctite to use to lock the nuts given they will be close to a source of heat, oil and vibration.

The usual blue Loctite threadlocker works for me on old motorbikes including engine bolts and nuts in a high heat, oil and vibration environment. Using the threadlocker means you can undo them when you want to. If you use Loctite retaining compound or red threadlocker rather than the blue threadlocker, you will need to use a propane torch to undo the nuts so it turns into a real chore.

Edited By Hopper on 09/05/2019 11:08:42

There's a wealth of really good information only a couple of clicks away, at the manufacturer's website...

Loctite change the numbers of their products from time to time, so what follows reflects my stock, not what the latest numbers may be. Hopefully, they haven't changed.

222, 'Super Screw Lock', is suitable where the fasterer that has to be undone has a long thread engagement. The amount of torque needed to break the bond will be related to the area of thread that is bonded, so avoid high-strength products for screws (in most applications).

243 is a medium strength preparation, stronger than 222, and is suitable for nuts, or where there is short thread engagement if screws are used.

These two will probably take care of almost all needs.

609 is a high-strength retaining compound, and if used on fixings, will be awkward to undo, without heat.

If you think the plethora of Loctite's retaining compounds is a nightmare, don't even think about their range of sealants, etc.!

Hope this helps.

I have a Loctite catalogue giving all grades/uses. A good reference is ARC Eurotrade's catalogue which gives their brand alternative.

+1 for Arc's Truloc range

Mick 🇬🇧

Just to add to the list, I've been using Loctite 248 for a number of years. It differs from a lot of other Loctite products in that it comes in stick form (like lipstick or Prittstick) rather than liquid which I find easier to work with. It is a general purpose, medium strength product that can stand a bit of oil on the surfaces being joined and can be undone with hand tools.

The manufacturer's blurb say it can work on threads up to M50 in size! I use it mostly on motorcycles on threads around M6 in size.

Henkel web site

I should just state that I am an ex-employee of Henkel so may be a bit prejudiced.

**LINK**

This is a good guide to Loctite stuff

Jim

Ask your supplier.

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Loctite 290 is a useful one to have for threadlocking. It is suitable for use on many threads after they are assembled as its very low viscosity allows it to penetrate by capillary action. It isn't likely to work on nylock nuts, or good fitting countersunk screw heads, as they may be too well sealed. It is a lower strength type, safer on small thread sizes.

I recently used 620 sleeve and bearing fit on joints which were likely to lock prematurely if 601 or 638 were used. It is just as strong, but much slower setting.

It is always best to make sure that threads are degreased first if Loctite is to be used, but once cured, most grades are unaffected by oil. Temperature resistance varies, most grades are ok below 300C.

Edited By old mart on 31/08/2019 22:00:41

The selection of thread lock will also depend on the temperature of the horn blocks. If they are attached directly to the boiler you could assume that they would be at the same temperature.

Saturated steam at 100 psi has a temperature of 170 degrees C. Loctite 243 is guaranteed up to 180 degrees. (200 at slightly less retention) and can be dis assembled with normal tools. Check the steam pressure/temperature tables if you are operating at a different boiler pressure. If higher temperature, you may have to use one of the higher strength Loctites but they will be harder to dis-assemble.

Paul.