Ohrndorf 5 Cylinder Radial

[petertha]

Group shot how they looked at this stage.

[Mike R]

Nice work!

[Dave Otto]

Beautiful parts!

Dave

[jcge]

The hand blending and finished items look great !

[Kim]

Wow!  Those are gorgeous rocker covers!  As you said, too bad you have to cover the rockers, but the covers them selves are little works of art, so it makes covering the rockers a little better 

Kim

[Roger B]

Looking good   

I made my tappet clearance adjuster screws from hexagon grubscrews cutting the radius for the pushrod with a ballnose carbide endmill. Not the best picture 

[petertha]

Thanks, I'll have to remember that trick.

[petertha]

The link rods were made from 7075-T6 mostly for strength. These do not have bronze bushings on the ends, just the aluminum itself and 2 oil holes. Four link rods are required plus spares.

The stock was milled to correct thickness. Two hold down holes were drilled on either end which aligns to a matching fixture plate. The wristpin & bottom end pin holes were drilled & reamed to size 5mm & 6mm respectively

[petertha]

Preserving this same setup, the sides were then milled to shape the dog bone profile. I set my table stops to the start & end points so this could be replicated. This was still my prior RF-45 mill, but I find these stops to be very useful so made the same for my newer mill

[petertha]

A center flute was milled using a ball end mill, again using the table stop. Then part flipped to do the other side.

[petertha]

The sacrificial ends with the temporary hold down holes were sawn off. The remaining part was relocated to a different fixture, mated to dowel pins corresponding to the wrist pin & bottom pin holes. It was secured with a small strap bar across the middle. This fixture was aligned to my rotary table, actually a tooling plate on top of the rotary table. The masking tape is to keep swarf out. Each end was milled to profile the round over ends.

[petertha]

One more fixture to align the part for drilling oil holes on both pin ends. The holes are at an angle to one another, but also slightly offset either side of center to help promote lubrication path.

[petertha]

Group shot after some chamfering & finishing.

[petertha]

I made a few modifications to the master rod design. Nothing relating to important geometry or dimensions, more cosmetic fillets, profile transitions, tooling availability or where I thought machining steps might be easier. Some dimensions on the plans were a bit confusing to me. So rather than invite a machining error on what is a time-consuming part, I tried to match features to fixtures or jigs at the same time.

I already had developed some prior section views checking for an issue to beware of on radials. That none of rod elements intersect with anything, in particular the link rods with the skirts of cylinder liners. I’ve read about some builds requiring unwelcome notches having to be cut late in the game. Because it’s kind of a 3D problem related to rod length, stroke length & part dimensions rotating & displacing, it may not be easy to visualize. Handy hint if you don’t have a means to detect interference. Do a lateral cross section at the face of the rod section, not through the center (which may falsely show sufficient clearance). It’s usually the corner of the link rod that will contact the bore at first at some angle. In my case, I had to pay attention to the liner bottom chamfer as well as the corner chamfer/radius on the link rods.

[petertha]

The master rod was made from 7075 aluminum for strength because it also supports the loads of 4 link rods and some of the cross sections there become pretty skinny. The stock was face milled to thickness as a block. All the holes were drilled and reamed where required in one setting for dimensional accuracy. You can see some holes become the internal fillets profiles between the link rod bottom end pin features. There are 2 small M2 screw holes to secure the crank pin bushing part. So, there is a front & back face to the master rod, otherwise the part is symmetrical.