Grub screws keep coming loose!!!

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Wayne j

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Hi, looking for some help. I am getting this nice little RMC engine up and running that I bought at an auction. The eccentric for the exhaust valve rod pusher is held by 2 grub screws so that you can adjust the timing of the exhaust valve. The issue I have is they keep loosening off in use and then the timing is off and engine will not run. I have tried some blue Thea’s lock but still keeps happening. I don’t want to use permanent thread lock as I won’t be able to adjust again later. Anyone have any tips on how to stop these loosening off the crankshaft? Thanks

Wayne
 

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Hi Wayne,
What about adding locking nuts to the grub screws in the same way the grub screws on the gibs on your lathe are locked in position?
Regards,
Alan C.
 
Hi Wayne,
What about adding locking nuts to the grub screws in the same way the grub screws on the gibs on your lathe are locked in position?
Regards,
Alan C.
Thanks Alan! I will give that a try. Hopefully I have some small locking nuts to fit.

Wayne
 
Get 2 screws half the length you are using now. Screw one in and tighten it up. Then screw the second one in on top of the first and it will lock the first one down.
And stick a note on the underside of the baseplate to remind yourself that there are double screws when you are working on it ten years from now.
 
Hi, looking for some help. I am getting this nice little RMC engine up and running that I bought at an auction. The eccentric for the exhaust valve rod pusher is held by 2 grub screws so that you can adjust the timing of the exhaust valve. The issue I have is they keep loosening off in use and then the timing is off and engine will not run. I have tried some blue Thea’s lock but still keeps happening. I don’t want to use permanent thread lock as I won’t be able to adjust again later. Anyone have any tips on how to stop these loosening off the crankshaft? Thanks

Wayne
Grub screws are made with at least five maybe six different types of ends. Flat, domed, cup,cone, knurled, and dog point. However in your situation Kiwi2 has a very good solution, and its the way Briggs and Stratton locks in their valves to set valve clearance. I probably would go with a cone and locking nut. This allows you to readjust the settings when you need to. At a hardware store you are probably only going to get the flat ones unless you special order. Looks like a nice little engine.
 
Here's a tip for avoiding setscrew (grubscrew) marks in your shafting.

Place a small piece of soft solder in before the screw - this hydraulics into place and holds quite firmly without leaving any permanent marks.

slug.jpg

Obviously less grip than if the screw bites into the surface but it works for most applications.

Here I am using it to secure my flywheel to my "6 Shooter" elbow engine - as the cylinders are Aluminium they would otherwise mark quite badly.

In some cases the ridge left by the screw can hinder removal or adjustment later.

I posted this back in 2012 but the photo vanished when Photobucket lost its mind.

I have subsequently had to retighten the screws after some settling in.

Ken I
 
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I have heard the solder trick before. Never tried it as I avoid grub screws for anything with a variable torque. Which is most things where modelers commonly use them. If you have say 0.00 in clearance between a wheel and shaft then use a grub screw to lock them, the screw forces the wheel to be half the clearance eccentric. Not a problem for many things, but not my choice. Also, where the torque varies, say when a flywheel is being accelerated on a power stroke then powering an engine on a compression stroke, the oscillating forces on the grub screw will almost always work it loose. Finally, where there is substantial torsional pulsations as in cams or eccentrics driving valves, then the peak torque of the pulsation often exceeds the material strength of the small local pressure point from the grub screw on the shaft, so worries the contact to failure. But I am biased, as I do not think they have many applications where they are OK. "Proper" engines (full size) almost never use them. Use keys, tapers clamps, etc. for "a proper job". I often use a simple "pipe nut and olive" that forms a double taper lock. Simple and carries high torque, especially oscillating torque applications. Does not work loose when properly made, and fully adjustable. IMHO.
K2
 
Thanks Everyone for all the feedback and great ideas. I will give some of these a try on the weekend so hopefully I can get this engine up and running reliably. Really appreciate all the help!

Wayne
 
I have heard the solder trick before. Never tried it as I avoid grub screws for anything with a variable torque. Which is most things where modelers commonly use them. If you have say 0.00 in clearance between a wheel and shaft then use a grub screw to lock them, the screw forces the wheel to be half the clearance eccentric. Not a problem for many things, but not my choice. Also, where the torque varies, say when a flywheel is being accelerated on a power stroke then powering an engine on a compression stroke, the oscillating forces on the grub screw will almost always work it loose. Finally, where there is substantial torsional pulsations as in cams or eccentrics driving valves, then the peak torque of the pulsation often exceeds the material strength of the small local pressure point from the grub screw on the shaft, so worries the contact to failure. But I am biased, as I do not think they have many applications where they are OK. "Proper" engines (full size) almost never use them. Use keys, tapers clamps, etc. for "a proper job". I often use a simple "pipe nut and olive" that forms a double taper lock. Simple and carries high torque, especially oscillating torque applications. Does not work loose when properly made, and fully adjustable. IMHO.
K2
I've not heard of a "pipe nut and olive" before. Can you point me to a drawing? I have an idea what this might look like, but not sure ...
 
Basically a double taper-lock ring (yellow). I use the term "Olive" as the idea is following olives used for pipe joints. (a familiar assembly for many DIY-ers). I have used actual pipe components where a convenient size (e.g. 6mm shaft = 6mm pipe!), or make my own sizes as required.
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What this is really doing is giving a full circumferential grip of the shaft by the tapered ring (compression ring) being squeezed onto the shaft by the blue nut, that screws onto the red flywheel/gear/rotor hub. If you split the ring (yellow) it still provides near circumferential grip, but can be easily removed.
Hence the "point contact" of a grub screw is eliminated, it is fully adjustable and provides hundreds times more torque transmission than a grub screw.
Simple? Effective?
K2
 
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K2 !
A good way to do it, I need it and I will try it
Thank you !
 
My British plumber uses this terminology: compression fitting & ferrule:

View attachment 150733
Interesting - at least in this part of the US, I have only ever heard of that as a compression fitting and ferrule, but I get the reference to an "olive" now! Yes, this should be a nicely effective way to achieve good grip on the shaft. I wonder if the "olive" / ferrule will be stuck to the shaft afterwards? That's what happens when I use this sort of fitting on copper or plastic tubing.
 
"compression fitting and ferrule" = the proper name. "I wonder if the "olive" / ferrule will be stuck to the shaft afterwards? That's what happens when I use this sort of fitting on copper or plastic tubing." - Yes, but if using pipe olives, then they are just consumable and can be cut off. But if you pre-split them they cannot stay put after the nut is slackened off. 2 splits, and you have a standard double taper clamp... Use an O-ring and you have a temporary fix that will take an incredible torque "for a bit of rubber"
Pitted Olives in a jar have a hole through the middle, and sort of tapered ends... Hence, Pipe compression fittings are called "Olives". Or maybe an engineer (or Popeye?) was thinking of a girlfriend?
I made a generator from 2 bicycle generators, where the permanent magnet rotor spins around the pair of fixed stators. The shaft runs through the whole lot - like a bicycle axle. the nylon holder for the 2 magnetic rotors is clamped to the shaft by a pair of "compression fittings and ferrules" - well, adaptations - so the 6mm axle uses brass 6mm ferrules (Olives) that I made. Clamped with nuts - from plumbing supplies (Why ever make a Nut?) - onto the nylon hubs that are threaded to suit. This arrangement is a simple adaptation of taper-lock fittings that I used many years ago...
I selected this without ever considering "grubby horrible little screws" - AKA Grub screws. Just because it seemed like an easy and suitable option, suitable for the Nylon hubs that needed clamping to the shaft. N.B. Non-magnetic materials used (Nylon, Brass, Stainless steel) where I don't want magnetic flux lost from the generator bits. - You can see in the first photo.
K2
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