Part 12 By Vince Cutajar

Next it’s the connecting rod. The plan was the best I could think of. There are no flat surfaces and nothing is parallel on this casting so I needed a flat surface to use as a reference.

Started out by roughly marking out the centre line of the beam of the con rod. Clamped the con rod on the mill table and shimmed the beam with feeler gauges to bring the centre line as much as possible to be parallel with the mill table (Photo 1 & 2).

I then slowly milled the big end and the small end to have a flat surface as a reference (the big end was about 1mm higher then the small end) (Photo 3).

With the con rod having two flat and parallel surfaces, I put it on the granite plate and marked out a centre line around the con rod. From this centre line I marked the big end and the small end for 0.5" width. Also marked the con rod beam for the correct width (Photo 4).

I milled the beam, big end and small end of the con rod.
Spent nearly half a day in the shop to drill and tap two 3mm holes in the con rod, 80% of the time to setup and 20% to mill, drill and tap.

Used an angle plate on the granite plate. With a toolmaker’s clamp, held the con rod lightly to the angle plate and nudged it vertical using an engineer's square (photo 1). I then used a clamp on the small end (photo 2). Checked again it was still vertical and used another clamp to the big end (photo 3).

I then transferred the setup to the mill table and squared it up. I had previously marked the position of the holes on the con rod. Using the needle point of the wiggler I put the spindle over both holes and wrote down the X and Y readings for each hole. Using a 6mm slot drill I milled both flats where the bolts will rest. Then using the previously recorded coordinates I drilled and tapped for 3mm (photo 4).

I setup the con rod in the vice sandwiched between two sets of parallels. The parallels were holding the con rod between the small and big end.

Today decided that the setup was good enough but just to make sure that this does not move I applied a toolmakers clamp on each side of the parallels.

I did the cut with a 1.5mm slitting saw at 300 rpm and a depth of cut of 0.2mm. I was not taking any chances. Eventually (after 64 passes) I finished the cut.

Drilled 3mm clearance holes in the big end cap. Cleaned both mating surfaces of the big end and bolted them together. I then clamped the con rod to the mill table and drilled and reamed 10mm the big end and 6mm the small end.
Set up the rotary table on the mill. I will be using these two tools  for the next operations. They are MT2 tapers which fit the hole of the rotary table. One has a 6mm and the other a 10mm shaft. I had made these during a previous build (not an engine).
Cleaned the sides of the con rod beam and marked both halves of the big end with a centre punch.
Con rod finished - after 8 days!

Drilled the oil hole in the small end with a centre drill. I was going to clean up the the I-section of the beam but then I remembered that in commercial cast conrods that part is left rough so I left it as is (nice excuse). Just gave it a lick with a Dremel wire brush.

Trial fit in the crankshaft and it turns smoothly. Removed some material from the front crankcase (where the con rod had some interference) with a Dremel and problem fixed.

Part one  part two  part three  part four  part five  part six  part seven  part eight  part nine  10   11   12   13   14  15  16  17  18  19  20  21  22  23  24  25  26  27