Engine Metalurgy

Al Hobbs · Sep 6, 2011

Before agreeing with Rossi to produce the A/A engines, I visited different factories. We discussed what materials were available from the various engine manufacturers.

As you know there are many different types of aluminum, bronze, and steel alloys. Each has its own characteristics, tolerances, and costs involved. It is not just the cost of the material itself, there is a cost incurred by how difficult the material is to machine. As an example, pistons are made of high silicon content aluminum. The higher the silicon content, the more expensive it is for the material plus there are higher machining costs. In addition, there are differences in the silicon grain. This is also a quality issue. The smaller the grain, the more consistent the material.

I relied on several people for their advice as to what materials would be the best choices for the A/A engines. Some of the people are noted boaters and engine gurus here on IW. Another happens to be my son who produces cutting tools for the aircraft industry.

Rossi was the manufacturer that agreed to provide the materials approved instead of using the most readily available materials. I am not saying that other manufacturers provide lower quality material. I am saying that the A/A engines are made of the materials that I have approved based on the advice of people I highly regard. I am definitely not using low cost materials to produce A/A engines.

Again, I am not saying that other manufacturers are using poor quality materials. There are many good engines available to the hobbyist.

Terry Keeley · Sep 6, 2011

Just curous Al, are the AA pistons cast or cut from bar stock?

John Knight · Sep 6, 2011

Al,

What is the silcon content % in the pistons? The majority seem to be 20% but the ones Brad Christy and Paul Stirton use are 30%, which are more durable but can be more brittle.

Al Hobbs · Sep 6, 2011

The A/A pistons are cast of 21% silicone content aluminum. The casting then machined. The A/A sleeve is mounted on a mandrel and the CNC equipment machines the piston to fit the sleeve. The fit is then checked by hand before it is accepted.

I had some 30% silicone content aluminum pistons made by Kalistratov for the K engines. He machined them from barstock.

Bar stock 30% pistons are very difficult to machine as the material is so brittle. It is easy to destroy the piston trying to machine it from 30%. It also can be difficult to break in. The 30% material will not lose its fit as quickly either.

The typical Italian produced piston is made from 19% to 21% silicone content aluminum.

Duck899 · Sep 7, 2011

Al, thanks for starting this post..... Is it still the one guy in the Rossi factory who checks each and every piston and sleeve assembly for fit? I know you had said he was very good at checking the fit of each piston and sleeve and had been doing this for quite some time.

Al, what about the crankcase? What materials are used in the case to enable it to hold its shape better with high temperatures vs other engine manufacturers?

Al Hobbs · Sep 7, 2011

No problem for me Greg.

The A/A engine crankcases are also modified with silicone to make them stiffer than aluminum alone. I watched the people at Rossi cast crankcases and each casting was inspected prior to acceptance. They cast one at a time, by hand. Because they do their own castings, when ever a problem is detected, the crankcase can just be dumped back into the melting pot.

I think that most of the engine manufacturers are very proud of their products. They all were happy to show me their operations, equipment, and the quality control methods used in their plants. The largest plant that I toured was Picco, the smallest was CMB. But, everyone was proud of their facility and products.

Al Hobbs