Alternative block?

Monday, December 02, 2013

Tags :  engine-structure

In the history of race engine engineering, many methods have been thought of, tried and used on a wider scale to manufacture engine blocks. We all know the most commonly used production techniques and processes, which are the creation of castings with additional machining and the fully machined from solid blocks. The latter is mainly used for drag racing engines and to a degree extend into road racing engines.

Apart from these two processes, you might have heard of the plastic engine, and although this is not a race engine, the materials and processes used are so unique that I did not want to overlook this as a production method. But this article will cover another manufacturing process which, although not unique is certainly not common in crankcase design and production. It is welding.

For me there is one simple question here, and concerns the issues as to why an engine fabricated in this way would not be competitive – what are the strengths and weaknesses?

First the strengths. In general an engine design is pretty straightforward, and many of the engine features – cylinder liners, crankshaft main bearings and so on – can be oriented in the three common axes, x, y and z. This lends itself pretty well to the fabrication process, since all the construction elements can be fixed before welding starts. Also, the machining could be reduced or at least kept to a minimum compared to a cast engine block, since for example oil drillings could be made from tubes.

Next the weaknesses. Welding several separate pieces into a single engine block requires a significant amount of time, and there’s the likelihood of introducing stresses into the piece. Welding will introduce heat-influenced zones into the part that might lead to crack initiation and distortion. With the proper approach this could be reduced to a minimum, although the question remains as to whether this will be enough. Given the fact that welds are very difficult to be controlled fully, the risk for leakages will remain.

But perhaps the most obvious disadvantage is that, to provide the best and most consistent welding quality, the various wall thicknesses should be as homogeneous as possible. Add to that the principle that the weld itself represents a rather small radius between the welded parts, which would lead to high loads in the weld. Combine that with the fact that the heat-influenced zone, also just alongside the welded area, has poorer mechanical properties than the base material, which would lead to an increase in wall thickness to withstand the loads. And as we all know, wall thickness is mass, and mass is not wanted in our race engines.

Despite all this I still believe that this production technique should not be forgotten, although a number of disadvantages need to be taken into account. Or, and this would be even better, solutions/improvements should be developed in order to overcome these disadvantages.

In writing this article my aim has been to generate some response or feedback from readers who could provide me with some more insight or examples of engines that have used this manufacturing technique. To my mind the opportunities are obvious, and simplicity deserves a chance. Although the fabrication of a welded engine would be significant in working hours, nevertheless, in relation to the creation of moulds and casting tools to create an engine block casting it would still be cost-effective, albeit based on small volumes or one-offs.

I’d be interested to know your opinion on this topic.

Written by Dieter van der Put

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Comments

One more option: an extruded block.
The best write-up I could find is at
http://www.autospeed.com/cms/A_1280/article.html, which is not at all technical, but gives an overview.
The all conquering Mercedes W196 comes to mind though it used a cast aluminum  crank case, the head and cylinder block was a welded steel assembly. The cylinder combustion chamber and sleeve were forged as one piece with ports added and water jackets with cam box and crank case mounts all welded in one assembly with multiple stages of stress relief and heat treating. The 196 was a 3000cc Supercharged 8 cylinder engine with two x four cylinder head/cylinder block assemblies mounted to the crank case with cam drive and main power take-off at the center. Other previous racing Mercedes used the welded head/cyl. block system as well. I'm sure other manufacturers did this too back in the day.

http://gnf10x.nefo.med.uni-muenchen.de/~hiha/bilder/benz_3l_desmo.jpg.


Another way to assemble a block or head from multiple parts might be Dip Brazing.

This from Wikipedia;
“Dip brazing is especially suited for brazing aluminum because air is excluded, thus preventing the formation of oxides. The parts to be joined are fixtured and the brazing compound applied to the mating surfaces, typically in slurry form. Then the assemblies are dipped into a bath of molten salt (typically NaCl, KCl and other compounds) which functions both as heat transfer medium and flux.”
Multiple types of metals can be joined using this method.

Brazing was used here in America on the Crosley CoBra  engine of 1946-49. Not sure if this was the head only or complete engine. Corrosion of the engine was a major issue at the time. The Crosley was a very cheap micro car made in the 50's.

Cheers, Paul