Engine Design for Beginners:
The Schroeder Victor 09

Created: Nov, 2005
Last update: Feb, 2007
Click on photographs to view in more detail


 

The Victor 09 is based on the crankcase casting Roger produced for the Motor Boys' version of the Vivell 099 diesel. Roger says he wanted three things in this engine: first, a crankcase based on easy to hold and machine castings. Second, a blind bore cylinder to eliminate the need for a separate head with attendant sealing problems. And third, external inlet, transfer and exhaust ports to eliminate the risk of loss of primary compression around a "drop-in" cylinder liner. The engine still needs a good seal between case and cylinder, but as these are just flat faces, this is easy to achieve with a simple paper gasket.

In discussing this topic with Roger, he highlighted to me an area that commonly causes problems for the beginner: obtaining the correct fit for a drop-in liner where this fit itself provides the isolation between the inlet, transfer and exhaust ports (as used on the Crompton EZE 3 seen here). This is an astute observation. I've never found this problematic, but as we know that others have, it becomes a thing to eliminate. I've mixed feelings about the screw-cutting required by the SSS and the Victor. Again, it comes down to the individual builders' skills inventory, but is something I'd prefer to avoid on Project #1. The displacement size (0.098 cuin; 1.6cc) for the Victor is just right in my opinion giving the a good compromise between size and ease of obtaining the required fits.

Roger admits that the left-hand thread on the crankcase nose may be a bit intimidating to a beginner and a bolt on nose would be simpler. He also notes that the prospect of honing a "blind bore" may give some pause, but says he has never had any trouble with this sort of cylinder, so the difficulty is more perceived than actual.

The problem, as such, derives from two problems. First there is the difficulty in honing the area near the roof of the cylinder. Second is the problem of bore taper. The "split expanding lap" that will be used by most builders takes on a conical shape as it is expanded. As we must insert it from the bottom of the liner, this will tend to induce a taper in the bore that is the exact opposite of what we require. To prevent this the lap must be stroked from the top down to the point where it almost emerges from the cylinder. This can lead to "bell-mouthing" the open end of the liner. It also depends of the operator acquiring a "feel" that tells them when there are no high spots along the important part of the bore. All this requires experience which the builder does not yet have.

Fortunately, these problems are mitigated to a fair degree by the fact that the engine is designed for spark ignition. Spark ignition engines run a much lower compression ratio than other types, so the piston does not need to get all that close to the roof of the combustion chamber. Sparkies are also a bit more tolerant of less than perfect piston/liner fit too, as many owners of old clunkers with almost no compression that still run will attest.

Roger's kit comes with step-by-step machining instructions from a guy who has been writing them for 40+ years and knows what a beginner needs to have explained in detail. Notice on the General Arrangement drawing how transfer passes through a port in the piston skirt into the totally closed off bypass channel. This significantly simplifies cylinder construction, maximises the cylinder flange contact area, and improves wrist pin lubrication while providing enhanced piston cooling—not that the latter two aspects are significant in the speed range expected of a beginner rated engine.

 

Ruler

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