20 cc Horizontal 2 Stroke Diesel

[Roger B]

As I had problems getting a good finish on the crankshaft for my horizontal engine (from the same material) I decided to experiment a little on this one. Following a suggestion from Jason B I tried an aluminium tip in the tool. This gave a good finish with cuts from 0.05 mm to 0.2 mm depth, the only issue being long curly swarf.
With the first shaft turned to 13 mm I hacksawed out the other shaft ready to turn. I was having some problems keeping the cuts straight and at the end noted that my hacksaw frame had started to crack  Time to spend some more money  this time on a Swiss frame.

[Roger B]

I finished roughing out the 2nd shaft and then noticed I had lost count/concentration somewhere and had gone down to 12mm instead of 13     

Not a complete disaster as I can either reduce the size of the bearing that side or turn the shaft down further and sleeve it for the bearing. I will continue with this crankshaft as I also need to drill oil passages along the shafts, nearly 60mm deep 2.5mm holes, another chance to scrap the shaft 

[Bertie_Bassett]

you'll have to call that 12mm shaft a 'design feature' maybe to ensure that's things don't get assembled the wrong way round??

[cfellows]

That happened to me on my latest build, the 2 cylinder horizontal IC engine.  I had designed it for a 3/8" main journal and went a few thou too far when finishing it.  So, I took it on down to 9mm.  Wasn't a problem other than I had to buy a 9mm reamer and some 9mm bearings that I hadn't had on hand.

Chuck

[fumopuc]

Hi Roger, that will give your engine some special character. I would not worry about the function.

[Roger B]

I decided to try and drill the oilways in the crankshaft. I had bought a couple of new standard length split point drills as well as couple of long 2.5mm drills.

I started with a standard drill which I took down to 40mm (also the maximum stroke of the tailstock). I then moved to the long drill which I fitted with a depth stop. Every 5mm I moved the tailstock back to clear the swarf. This went, luckily, without  problems 

The webs were then cautiously drilled as I was expecting problems when I broke into the crankshaft holes, but again no problems 

Finally I used the long drill again to drill through the crankpin. The holes in the crankshaft and crankpin will be closed with M3 grubscrews.

I still need to drill through the crankpin itself, but am not sure whether to go on the outside (max pressure at TDC), on the compression side or on the firing side 

[Steamer5]

Hi Roger,
 Nice skills! Bet you were happy that the deep drilling went well. Have you decided whether its a keeper or a test piece yet? Looking like a keeper to me!

Cheers Kerrin

[Roger B]

Thank you Kerrin, yes it's a keeper

I bought a 11.5mm reamer for the 'feature' side. Both crankshaft halves and the outside of the webs were finished without problems, the rest of the feature side was reduced to 10mm.

The crankpin and crankshaft borings were then tapped M3 for the grubscrews. The holes through the webs will be closed by the balance weight fixing screws.

The crankpin was then centred in the Hemingway Keats and the inside of the webs were finished. Once again the chuck guard from my minilathe was pressed into service.

[Roger B]

The 14mm wide crankpin meant I could just finish it with my 6mm LH and RH tools. To start with I took the centre to just above size with an 8mm straight tool.

The final tasks were to mill the end of the webs to length and drill the oil hole in the crankpin. This was started with a 1.6 mm centre drill and finished with a 1.6mm drill. Is this too small or too big 

[Brendon M]

Looks good, well done

Drilling the oil holes would make me so nervous. Seems like if something goes wrong you'd need to start again from square 1. Or is it not as bad as I think?

[Roger B]

Thank you 

As I see it if the drill breaks you start again    Maybe the remains of the drill could be removed with some sort of spark erosion, but not many people have that available  .

For that reason I decided to try this on a shaft I had already made a mistake on. Even so the cost of another piece of C45k and a tip would still have been less than the cost of the 11.5mm reamer but I couldn't face all the hacksawing again.

[Roger B]

I turned a pair of top hat bushes for the main bearings from piece of 19mm bronze rod. These were pressed into the side plates and reamed again. It all fits together although I need to increase the end float a little (currently zero). Another crankshaft I can twiddle 

[Roger B]

Next step the connecting rod. There are always a number of different machining sequences depending on the details of the rod. This one is too long to mount on the faceplate so any boring has to be done on the mill.

As I wanted to radius the big end cap it was easiest (I think, suggestions welcome) to do this before the cap was cut off. To keep everything aligned I set up the angle plate with a V block as a fence so The centers for turning and for the bearings were all referenced to the same surface. The little end was reamed out to the final 10mm dia. and the big end was reamed to 6mm to match the pilot on my RT. I thought about adjusting the centers to compensate for the 0.8mm slitting saw but in the end decided that this was not really necessary (0.4mm in 80mm).

[Roger B]

While the rod was on the angle plate two flats were milled for the big end bolts then it was moved to the RT to round the end.

The cap was cut off with a slitting saw in the lathe and the holes were opened up to 3.1mm and counterbored. The holes in the rod were then tapped M3 and the cap was fitted back on.

[Roger B]

The basic shape was turned between centers, using a 3mm radius tool to blend the rod to the ends.