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More Diesel

Decades ago I liked to restore derelict model aircraft engines. In the 60's that usually meant Cox Babe Bee glowplug motors. Although I now prefer compression ignition (“diesel”) types, the pastime remains what it always was.

Over the years the principle remains unaltered: buy low-priced items that are no longer of interest to their owners and refurbish to running condition. Once-upon-a-time the school quadrangle was the dealing ground but today it is called internet. The quad is now infinitely larger, nobody is your friend and the goods offered have to be judged by means of (vague) pictures – good luck to you!

The above-pictured trio is a typical internet buy in the low-priced segment. The first two examples appear to stand a fair chance of restoration but number three is definitely destined to be stripped for it's last few parts.


We have here a 2,5 cc Webra Bully (or is it a Komet?) and a 2,5 cc Taifun Rasant – both popular German engines that date back to the 50's and 60's. By the look of it, neither has seen much action since then. After their last run the fuel residue (mainly castor oil) was not wiped off and the motors were not turned over with cleaning oil. The dried-up castor oil has now severely gummed up the internals and so becomes a threat in the event of inexpert attempts to loosen or dismantle the engine by force.

How these two oldtimers end up can be seen below. To start off with they are immersed in acetone for at least a week in order to dissolve the tough brown muck. Acetone will not attack the anodized parts which add so much charisma to old model engines. Stirring and shaking stimulates the process.

Important note: some old motors have color-decorated blocks, occasionally of a Hammerite nature. Such finishes are probably NOT resistant to acetone and other aggressive solvents and it is advisable to therefore soak them in petroleum.

The acetone bath is seldom the whole solution however – penetrating oil (“the blue can”) and the heat gun are next up. Holding the hot engine in an old rag – never ever bolt or clamp it down – carefully twist the prop back-and-forth. If that does not help then simply repeat the oil-and-heat procedure with patient twisting. Using the straw, squirt WD40 onto the piston and crankshaft (through the air intake) in order to cool these locally. Attempting to dismantle a gummed-up motor will probably end in destruction.

The two old Germans are destined to earn their keep in model aircraft so they are not polished up to display standards – simple cleaning makes them pretty enough.

This internet acquisition has a happy end because the two old diesels proved to have excellent compression and be good runners !