Engine mounting additional thoughts

[gary davies-jones]

With reference to Alex Whittaker's article on mounting engines,

I am surprised he has not made one mention of "thread lock" or "stud lock." This is technically speaking an anaerobic adhesive, that is to say a glue that cures in the absence of oxygen. Used to lock a thread in place it is applied to the thread at the point of final assembly, and when cured helps to prevent the thread from vibrating loose.

I was introduced to it by a fellow biker when I had a Ducatti 450 single. Now this beasty vibrated like a .......... well it vibrated a lot, and as a result used to unscrew and shed all sorts of excess weight. On one occasion (the final straw) left me trying to stop a bike with the handlebars in my hands, but not attached to the steering yoke. Now a complete strip down and rebuild with stud lock later it cured it's weight saving habits completely.

A cautionary tale here though some of the larger bolts later took the efforts of a 24" (that's 600mm in metric speak, give or take 3/8th's) breaker bar to release.

There are two types of thread locking compound out there as well as several manufactures. The two basic types are:-

1. The type that hardens totally, and
2. The type most useful to us modellers that remains slightly less than solid.

The later is the one I favour in fixing any small thread as it will release with a little effort, though I would agree whole heartedly with Alex. Use hex headed bolts or set screws as these are far less likely to slip or round than pozidrive or phillips headed items. All of my models are assembled with thread lock, and none so far have suffered any loss of components, and that includes a highly tuned 1/8th scale off road buggy which revs to over 50 000 RPM.

In short then the tips are:-

1. Use the semi hardening type.
2. Use hex headed screws.
3. Use only very small drops on each thread.
4. Use only for final permanent installations.

Gary Davies-Jones

[Steve Hargreaves - Moderator]

Nyloc nuts are often the best thing to use.....

[gary davies-jones]

True Nyloc nuts are good, HOWEVER, as Alex points out best only used once then replaced, and how many of us are guilty of reusing them? Me Sir! guilty as charged.

The other point here is Nylocs are only of use if the fixing is a through hole with sufficient clearence for the nut. Threadloc on the other hand works in blind tapped holes. It will also work on machine screws, AND the much maligned (unfairly I feel) self taper. Mind you I have yet to see a self taper with a decent head (eg hex), and yes I know there are hundreds of Torx headed self tapers in my car holding all sorts of things trim like in place, but these are a bit on the big side for model use.

for me it's still studlock/threadlock that wins.

Gary

[Martin Harris - Moderator]

I was told (quite a long time ago) by a BGA glider inspector that it was acceptable to re-use Nylocs for full size applications as long as they were "too tight to move on the thread without tools". I suspect that this rule of thumb might not be totally acceptable to the powers that be but at least gives an indication...I've adopted it for all sorts of motoring and modelling applications without any fastenings coming loose that I'm aware of.

Looking at Wikepedia, it quotes the American FAA as saying that they are re-usable if they still comply with torque specifications although the USAF don't seem to agree - but tthen hey're spending tax-payers money which may give them different priorities!

[gary davies-jones]

Ha Ha the good old tax payers dollars. I have heard this "too tight to move without tools" quoted about nylocs as well.

However Ref my Ducatti:- it still amanged to unscrew Nylocs that had been prviously used once.

Still miss that bike. Though not quite sure why. It was vibratory, noisey, drank oil, stopped dead in a light drizzle at the same time as trying to electrocute you, and broke final drive chains on a regular basis. On the upside however it went like a scalded cat, and handled like it was on rails, and of course being Italian looked....well....sexy. But I digress.

It probably is true that if you can't move a nut by hand then model engine vibration is highly unlikely to do so. Just one fly in the ointment thought:- how hot to engine mounting bolts get? hot enough to soften the inserts on a nyloc nut?

Ohh the negativity! Cries my wife. I just like to be safe, and try avoid problems real or perceived.

Gary

[Bob Cotsford]

I've reused nyloc nuts many times and over many years and never had one come loose.

Gary, the engine mounts shouldn't get anywhere near hot enough to soften the nylon inserts, not unless your engine is in real trouble!

[Steve Hargreaves - Moderator]

Posted by gary davies-jones on 09/05/2012 15:37:37:

It probably is true that if you can't move a nut by hand then model engine vibration is highly unlikely to do so. Just one fly in the ointment thought:- how hot to engine mounting bolts get? hot enough to soften the inserts on a nyloc nut?

Gary

Not hot enough to melt or even soften nylon I would say......our glow engines run relatively cool & the prop wash keeps the suroundings pretty cool too. I would think that a bolt that got hot enough to soften a nylon insert would soften threadlock too.....I always apply a little heat when I want to remove a threadlocked nut or bolt.....

[Phil Claridge]

with the flair grey engine mounts, i drill a 2.5mm hole then use a 3mm set screw driven in by a low speed battery screw driver. this method seems to work very well and i have never had one come loose, even after changing the engine 2 or 3 times. but it's a real pain if you have to wind it out with just an allen key

[Former Member]

[This posting has been removed]

[John Olsen 1]

So was it a desmo Ducati? I seem to recall that the 450 was. Guy I worked with had one at one stage, I only had a Triumph 250 single at the time, another with the habit of shedding parts.

If you are using the correct grade of locktite it is usually not a problem to undo things, the torque should not actually be too much higher than the normal tightening torque. That is the theory anyway, I have had my moments with it, and lso with the plastic gasket from the same outfit, where I could not get the sidecovers off the engine ( a Honda in that case) without heating them. Heat is actually the answer if the stuff won't come undone, a hot air gun will usually do the trick. This may not be very applicable in the model case, since you may not want to heat any covering nearby. For small parts you could try heating them with a soldering iron.

You don't always have to put locktite on before you do it up, if you apply a little to the interface between the nut and screw it will wick in. This is not applicable to tapped holes under say an engine where you can't get at them but can be handy at times. Don't use too much as it will wick for miles given the chance. The Aussi airforce nearly lost a Mirage over that.

regards

John

[gary davies-jones]

Yes John it was a desmo. Half of a 900SS. Probably why it was so out of balance.

Back to locking screws though. I have recently experimented with hotmelt. It used to hold the pints into arrow shafts very effectively, even when pulling them out of taget boss tripod legs, wonder how I found that out.

So far no failures, I'll let you know how it works out.

Gary