Saturday, October 17, 2020

Small Shop Update

Where "small" modifies update, not shop.  

Not much has happened with my little Webster ICE (internal combustion engine) since my last update two weeks ago, not because of lack of trying, just lack of success.  One part I made has been giving me fits.  This one; a counterweight design I copied from the web without details and apparently didn't make properly.  

The sizes aren't very obvious - you can see by the out of focus Q-Tip on the left that it's not an enormous part.  From the center of the radiused curve at the top to the bottom of the bottom radius, it's 1.82".  
There are two shafts visible.  Both of them are 5/16" drill rod;  0.3215".  The problem is with that lower shaft protruding behind the part, there's too much of a gap between the shaft and plate it goes through.  That's a quarter inch thick aluminum plate.  It's too loose a fit (meaning I made the hole too big) and Red LocTite has broken twice - the latest time today.  I need that part to fit where it goes to determine the thickness of some spacers I need to make that will go on the shaft (it's the crankshaft - that short one facing you at the top drives the piston).  

With the shaft out of there, I compared the hole to a reamer I have that's .001 oversized.  The oversized reamer drops through the hole without touching it, and calipers (which are not the way one really measures a hole) say it's closer to 0.317 which is insanely out of spec.  I have to think I just used a drill bit.  That's just plain not good thinking on my part.  One of the things that has slowed me down is waiting for LocTite to cure on this part. 

I should probably just remake the part.  It was cut on the CNC mill and I'm sure I have the file somewhere, or can re-create one.  Since I've tried LocTite twice, I don't think that's going to work for me.  I've read many places that a good alternative is to knurl the part, which forces some metal up around the cuts it makes.  I don't know if that's going to be enough to get it to fit, but it's going to be better than what I have.  

My only success has been making an adapter from the RC engine carburetor to the intake port on the engine.  This part works acceptably well. 

The adapter is on the left, from the odd-sized port on the carburetor to the odd-sized port on the engine. 
I still need to order a fuel tank (or make one, which frankly seems like too much work) and make a few odd little parts that will take minutes to make.  


  1. there's too much of a gap between the shaft and plate it goes through.

    Sounds like a job for an oilite bushing.

  2. Supposed to be a press fit, yes? Can you make another shaft out of thicker material and turn the the part that is pressed in to .001 oversize, turn the remainder to 5/16"? Putting that aluminum in the oven should make a reasonably easy shrink fit.

  3. Very cool, SiG!

    I found a kit of finished parts for a small two-cylinder vertical OHV four-stroke engine.

    I'm sure I'll post pix of it if it ever gets here!

  4. Take a look at, sleeve bearing 6391K403. According to the information you provided, that "will" fit if you ream out the hole a little bit per the info at MM. Another option is 6377K5.
    Contrary to what some people say, Loc-Tite is NOT a miracle product. I stopped specifying it 10 years ago. And don't get me started on Gorilla Glue...
    As to knurling it, that doesn't strike me as a good idea. Too many chances for metallic particles to get into the works, and I don't think the raised edges will support much of a load. One problem with knurling is that wear reduces the knurling. If one is lucky, then the wear is even; if not, well, uneven wear results in changes to the axis of rotation. This does not end well.
    Mechanical Designer, specializing in Unigraphics solid modeling.

  5. Yes peen. Take a center punch and hammer 10 or so times equally spaced around the outside of the shaft, that should upset enough material to give a tight fit. Or if that is not enough use a sharp cold chisel and hammer two or three longitudinal cuts to give you enough that it will need a press to get it apart. TeX.

  6. Knurl the shaft, freeze it, heat the plate, hammer them together. Or, drill through both plate and shaft and pound a little roll pin through to hold them together. Maybe even do both!