Author Topic: Snow engine frustration  (Read 3126 times)

Offline GordonL

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Snow engine frustration
« on: July 06, 2017, 08:04:16 PM »
I am coming to the end of my build of my Snow Tandem engine and it is getting frustrating. My big problem at this point is keeping everything hanging together. The set screws loosen up no matter what I try to do. The cams and the timing gears are held in place with 2-56 set screws and every time I try to start the engine one or more of the setscrews loosen up. I have machined a flat on the cam drive shaft but they still loosen up. There is not enough depth to place another set screw on top of the first set screw to lock it. That is what I did with the pistons because the pistons also came loose. The coupler holding the two piston rods also came loose so I put opposing set screws in the coupler and that now seems to be holding. I do not want to put loctite on the setscrews because I am sure that I will have to take it apart again. There is only so much pressure that you can put on a 2-56 setscrew especially in a brass gear.

Not much any of you can do for me but I feel better when I vent. Some day it will all just come together and everything will work just fine.

Gordon

Offline Jasonb

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Re: Snow engine frustration
« Reply #1 on: July 06, 2017, 08:09:42 PM »
Use a screw or nut lock 221 or 222, they are designed to stop fixings vibrating apart but can easily be undone with normal tools. Failing that dab of paint or nail varnish.

http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802623422465
« Last Edit: July 06, 2017, 08:18:04 PM by Jasonb »

Offline crueby

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Re: Snow engine frustration
« Reply #2 on: July 06, 2017, 08:15:28 PM »
Or loctite blue, it will stop it vibrating off, but is still removeable without having to heat the parts. Hope you can get a solution!

Offline Walsheng

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Re: Snow engine frustration
« Reply #3 on: July 07, 2017, 01:50:48 AM »
I use blue locktight on my RC helicopters and as you can imagine there is a LOT of vibration.  It holds very well but allows you to take it apart.

John

Offline gbritnell

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Re: Snow engine frustration
« Reply #4 on: July 07, 2017, 01:19:10 PM »
Hi Gordon,
The problem is even the slightest amount of radial twist will loosen the set screws. I discovered the problem with my flywheels to crankshaft attachment. Now whenever I can I use some type of key to prevent the twisting action. That way the set screw just keeps the part from moving axially.
I even do this with gears. For the key I just drill the shaft with an appropriate sized drill and put a pin in it.
For the gear or whatever I don't want twisting I drill a hole axially along the bore. To accomplish this I make up a shouldered bushing made from the same material as the part and drill the hole through the shouldered part. This provides a true pilot for the drill. I then slip the bushing into the part and drill into the pilot hole. This will keep the drill right on the joint line. It's amazing that just that small of a pin will keep the part from twisting and the set screw just has to locate the part.
gbritnell
Talent unshared is talent wasted.

Offline crueby

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Re: Snow engine frustration
« Reply #5 on: July 07, 2017, 01:28:28 PM »
George - I think I follow what you are describing, but could you post a picture or two of it? Sounds like an interesting method.
Thanks!
Chris

Offline Doc

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Re: Snow engine frustration
« Reply #6 on: July 07, 2017, 02:38:33 PM »
Hi Gordon,
The problem is even the slightest amount of radial twist will loosen the set screws. I discovered the problem with my flywheels to crankshaft attachment. Now whenever I can I use some type of key to prevent the twisting action. That way the set screw just keeps the part from moving axially.
I even do this with gears. For the key I just drill the shaft with an appropriate sized drill and put a pin in it.
For the gear or whatever I don't want twisting I drill a hole axially along the bore. To accomplish this I make up a shouldered bushing made from the same material as the part and drill the hole through the shouldered part. This provides a true pilot for the drill. I then slip the bushing into the part and drill into the pilot hole. This will keep the drill right on the joint line. It's amazing that just that small of a pin will keep the part from twisting and the set screw just has to locate the part.
gbritnell

Good point George! 
   I have done something very similar I drill and tap for a second set screw down the same as you are describing and instead of a pin the second setscrew gets tightened. I have found that this works better than cutting a key way in the gear, pulley or flywheel and shaft its on.   

Offline gbritnell

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Re: Snow engine frustration
« Reply #7 on: July 07, 2017, 05:01:55 PM »
Hi Chris,
I made a quick sketch to try and show what I'm talking about. This is the basic idea. If the drilled hole is around .047 after drilling you can square it up using a jewelers file. My files are .045 wide so they make a nice square slot. You can then make a key by turning a short boss the diameter of the hole and then milling away the remaining stock making a standard looking key with a round boss in the middle of it.
gbritnell
Talent unshared is talent wasted.

Offline Doc

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Re: Snow engine frustration
« Reply #8 on: July 07, 2017, 05:42:13 PM »
Ah we are on two different wave lengths  ;) I was talking abut a shaft end totally different than what you are showing. Thats an excellent Idea I'll keep that in mind.
  Thanks for the tip!

Offline crueby

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Re: Snow engine frustration
« Reply #9 on: July 07, 2017, 06:09:57 PM »
Nice, thanks!

Offline GordonL

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Re: Snow engine frustration
« Reply #10 on: July 08, 2017, 03:25:17 PM »
George. I have done similar things but in this case there are four cams (1/4" wide) and one brass gear spaced along a 3/16 dia shaft. Your method works well on a bore which comes out to the end of the shaft but when it is along the shaft and there is no room for something like a bushing.

 

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