Harvard/Stickney Jr Model

[JPar]

You have to be careful about putting the setscrew over top of the key.
Make sure that the hub is thick enough, where both the key and setscrew will be.

That's a good point. I took a closer look at the hub, and after subtracting half the thickness of the key, I'm not sure there's enough "meat" left for the screw. The drawing actually shows the key and set screw placed 180 degrees apart, but I don't like that because the burr left by the set screw can make if difficult to remove the gear.
For this application (camshaft), I wonder if it would be sufficient to omit the key, and just mill a flat on the shaft for the screw to bear on. I wouldn't think a camshaft gear would be subject to the same loads as a flywheel on a crankshaft. Thoughts?
John

 

[Barnbikes]

Keep the key and mill a flat 180 degrees for the set screw.

 

[JPar]

I got distracted by other things, but finally got back to the cam gear. I broached the gear and cut a keyway in the shaft, 180 degrees opposite the set screw as suggested. I also milled a flat for the set screw to bear on. It was my first attempt at cutting a keyway in a shaft. I'm happy with the way it all came out!
John

 

[JPar]

I'm finally getting back to the little Stickney after a hiatus of 9 months or so. It's starting to come back together now. Last week I assembled the crankshaft, base, eccentric shaft, and flywheel. Yesterday I assembled the piston, sleeve, cylinder casting, and top casting.

 

[Tim1974]

Looking good stick at it

 

[gbritnell]

It's coming along great!

 

[LorenOtto]

I'm finally getting back to the little Stickney after a hiatus of 9 months or so. It's starting to come back together now. Last week I assembled the crankshaft, base, eccentric shaft, and flywheel. Yesterday I assembled the piston, sleeve, cylinder casting, and top casting.

View attachment 128882

Very glad to see you are back at it - keep the posting coming.

 

[JPar]

The little Stickney is back together and essentially complete, except for some work on the ignitor. I've set it up for spark plug ignition, so the ignitor work can wait. I tried to run it and got a few putts. But then I discovered a serious issue. The crank throw, which is supposed to be a tight press fit, is slipping on the shaft. It's really frustrating and depressing to discover this at this stage of the game.
I disassembled the engine. Here's a photo of the crankshaft, showing the throw and crank pin. There are probably a couple of ways to fix this. I'm thinking of drilling and tapping for an axial set screw, which will be half in the shaft and half in the throw. There's probably a name for a screw like this, but I don't know what it is. The second photo is a crude drawing, trying to illustrate what I mean. The drawing also shows a set screw to ensure the crankpin is secure. I'm thinking that might not be a bad idea, and it's relatively easy to do while everything is apart. There's very little twisting torque on the pin, but it would be a disaster if it were to work its way out of the hole.





I'm thinking of using #8 screws. The crankshaft diameter is 0.500. The pin is a little smaller.

What do ya'll think of this approach?

Thanks,
John

 

[JPar]

I decided just to go for it, and made the fixes as described in my previous post. I used 2 #8 screws to secure the throw to the shaft, and 1 #8 to secure the pin to the throw. It looks pretty good to me.

 

[JPar]

Here are a couple of photos of the little Stickney, reassembled with the repaired crankshaft. The engine is more or less complete, with the exception of the ignitor which is non-functional at this point. I've rigged the engine for spark plug ignition, with an electronic buzz coil and hall sensor for timing.
I've run the engine a few times, but never for more than about 30 seconds or so. It ran fairly well for short periods, but then stopped for reasons that I'm not yet sure of.
During the last run, the head gasket blew out. Fixing that will not be easy, as the head is actually inside of the cylinder casting. It will require a complete disassembly of the engine. I think I'm just going to put it aside for awhile and work on other things.
John





Here's a short video of it running.

 

[JPar]

I just realized I should have put something in the pictures for scale. The engine is about 25 inches tall, including the wood base and the brass fuel tank on top.

John

 

[JPar]

During the last run, the head gasket blew out. Fixing that will not be easy, as the head is actually inside of the cylinder casting. It will require a complete disassembly of the engine. I think I'm just going to put it aside for awhile and work on other things.
John

I put this aside a few months ago, and it's time to try to fix it. After reading some older posts about gasket material, I think I'm going to try Teflon sheet. I have a question for those who have used this successfully. Should I use any type of sealant with the Teflon, or should I just leave it dry?
John

 

[Stefan-K]

Hey John

If you are using Teflon sheet as gasket material there is no need to use any kind of sealant. Just leave it dry. Mostly i use Teflon sheet with a thickness of 0,3 to 0,5 mm. That`s enough. But remember Teflon tends to flow away under constant pressure and heat, so a sheet too thin will leak again after some time.
Stefan

 

[Mike Ginn]

In my experience you should never use plastic sheet of any kind as a gasket. Basically they all flow and at some point leak and PTFE (Teflon) does just that. I always use proper fibre (fiber!) based gasket sheet which is readily available in a range of thicknesses and easily cut - ideally using a cnc craft cutter but it works with scissors and or craft knife.
Mike

 

[JPar]

In my experience you should never use plastic sheet of any kind as a gasket. Basically they all flow and at some point leak and PTFE (Teflon) does just that. I always use proper fibre (fiber!) based gasket sheet which is readily available in a range of thicknesses and easily cut - ideally using a cnc craft cutter but it works with scissors and or craft knife.
Mike

Mike, could you kindly provide a little more information. What sort of fiber/fibre are you speaking of? A link to a specific product would be helpful.
The gasket currently in the engine (the one that blew out) I made from a standard paper gasket material, commonly available at auto parts stores here in the U.S. I want to try something different this time.
John

 

[Mike Ginn]

Hi John
I use a material called Flexoid (0.25mm thick) which is made in the UK. It does appear on the US version of eBay and I have provided the link in the attachment. The sheets I use comes as A4 size which is about the size of your Letter paper. I am not sure how larger a gasket you need. You could use annealed copper sheet which is the traditional gasket material.

If you have difficulty getting this material I could send you a sheet in a letter envelope or a sample.

I can also explain how to cut out the gaskets using a cnc craft cutter - its not straight forward and uses dxf files.

Best of luck

Mike

 

[JPar]

Mike, thanks for the information and the kind offer to send a sample. I will keep it in mind as I consider all the options. Ideally, I'd like something a little thicker, e.g. 0.015 inches (0.4 mm) or so. The gasket is relatively small - approximately 2 inches (50 mm) in diameter. I do not have a CNC craft cutter, so no need to explain that.

While looking at Flexoid on eBay, I came across another option I'd never heard of. Does anyone here have experience with "flexible graphite foil sheet"? The information I found suggests that it's good for high temperature automotive use, so perhaps it would work OK for models? It's available here in the US.
John

 

[JPar]

Got the engine apart, and verified the head gasket is indeed blown.

 

[JPar]

I made a new head gasket from 0.4 mm graphite foil sheet. The engine is back together, and with a little fiddling is running pretty well now. I took it to a show this weekend and ran it for at least 2 hours over a three day period. The new gasket seems to be holding up so far. Here's a video:

John