Another (unsure) Upshur twin (lots of beginner questions?)

The build is looking great so far ! Nice work !

Timo, see my comments about the conrod hitting the liner and my suggested fix

https://www.homemodelenginemachinist.com/threads/upshurs-opposed-twin-engine.36037/post-410429

9mm at the bottom and 6mm at the top would also work

The cam shaft gear was made today. (from some cold rolled mystery steel) I have a 0.5 module hob, i decided to go with that.
0.5 module gears compared to 0.528 module gears (aka 48 pitch) have little smaller teeth. So I adjusted the counts from 30/60 to 32/64.
That pair would have a center distance of 24 mm which is then 0.18 mm too large.
I try to leave both blanks 0.18 mm smaller in diameter, and keep the tooth depth same. I am hoping I will get away with it.
Thre blanks, one was in the middle, so the burr is very small, one has a burr on the climb cut side and the 3rd one has a little messed up tooth profile.

Deviating from the schedule I gave the crank shaft a try.
I found a big plate hot rolled steel 16 mm thick. I could cut a strip off with the band saw that was roughly the proper length.

Drilling center spots on both ends, using the toolpost as the workholding, with the center drill in the collet block. For height I made a scribe line, for distance using the digital helper.

Interrupted cutting at low rpm with patience went almost uneventful. (The plan suggested to drill and mill out parts before, but I went with plunging directly) The most irritating thing is that the part becomes "transparent" which requires a lot of attention.

The burr in the last plunge cut was quite big, but it went away as soon as the diameters of first and second plunge cut matched. I made a block that fitted nicely into each gap.

To keep the corners sharp on the crank I made a left and right hand skinny parting tool.
The first trial was totally annealed, because of insufficient patience and cooling. The second went flying, when I wanted to touch up the front angle.
Number 3 and 4 were better. (0.5 mm wide)
After lot more work, interrupted cutting I have my first single piece crank shaft. Might need some modification later. (is a little bit too long on both ends and no gear mounted yet.




Greetings Timo

I made the carburetor body on Monday.


Throttle and jet took a while, small stuff.


The needle is not done yet. Is that a part that needs to be moved a lot? I could make it from a cap head screw, but it would require a hex key to adjust. Or I have to make the complete thing.

Next up the connecting rod. Took a lot of time and head scratch how to make those. I drilled the threaded holes in the longer part and through holes into the shorter block. The shorter block is a little higher than it needs to be. That allows to find the exact line were the two parts meet with the edge finder.



Grrr, after cutting I noticed that I put the stock upside down into the vise, so the threded holes ended up almost outside of the part (not were they should be). So I had to make a new part.

This time the threaded hole is inside the part not under it. ...

Then I made a sort of a grip fixture to hold the small parts. A shape of the connecting rod with recesses to grap the bosses.

I thought of gluing the parts in, but how to get them out again, and then I had the idea to make a simple cut with the band saw, so that it can be clamped with the vise. (worked quite well)

Both sides cut, so most of the "big block" disappeared.

After test fitting them to the crank.

I was not confident about the soldering of cast iron (maybe some other time). The crank case will be made from aluminium, so I thought I give threading a try.

The bore was quite bad after turning. I reamed it with an adjustable hand reamer, hopefully good enoug.

The wall thickness is not exaclty big, were the undercut of the thread is. Is it enough? 1.5 mm



The crank case is missing the top and some of the threads for mounting things.

p.s. lots of parts still to do.

1.5mm Wall should be OK