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Monday, January 28, 2013

Webra 2.5 S Rebiuld Project



Webra Model 2.5 S
Manufacturer/Distributor Webra-Fein-Modelltechnik, Berlin, Germany
Year of manufacture 1951
2.45 Displacement DC (0.151 cu. In.)
Bore 14 mm (0.551 in.)
Stroke 16 mm. (0.630 in.)
Diesel Power Class
Cycle 2
Fixed type carburetor (without speed control)
Admission front rotary valve (crankshaft)
Crankshaft on bronze journal
Fuel:- / Castor oil / Kerosene /Ether
Worn Condition with missing parts before rebuild

Comment the "S" stands here stands for Seitenflansch (Side Flange) and not for "Sport" 




2 needle valve version shown below


This is the story of how I produced this lovely collectible vintage diesel engine

from this sorry collection of worn out junk parts: by investing many hours of painstaking work


and creating this final product, a fine running rebuilt Webra 3.5 S diesel engine


The condition summary before rebuild: missing connecting rod and counter-piston; incorrect propeller driver; badly worn piston and crank pin as well as an overall rundown condition; the crank pin when new measured 5 mm in diameter but, this one is between 4.67 and 4.84 mm, a sort of egg shape with a badly scratched surface; the soft copper gasket between the cylinder liner and the crankcase was also missing. The next few pictures show the making of this simple but essential part


After the final size of the inside and outside diameters is achieved by the machining operations the washer is carefully cut off with a Dremel tool, to prevent warping of the soft copper part 


Then a file is used to remove the sharp standing edges until we have a flat ring of soft copper




The making of this simple part took more than an hour of work to produce, which is why engine rebuilding has to be a labor of love


After all that work it now looks right and seals well, that's why I do this: the reward will be an easy starting reliable runner





Contra-Piston machined with a conical recess that matches the conical dome on the piston


All parts are cleaned; the crankcase buffed and scratches eliminated, the head repainted with heat proof paint~~slowly we are beginning to see the results of these efforts


The next step is to select a suitable wrist pin from my collection of needle bearings, one with the correct diameter to match the piston


These needle bearings are perfect for this application: made from hardened silver steel with a chromed surface all assuring a long life for the final part


Now we must make the small end of the connecting rod and the pin bore in the piston to match the size of the wrist pin


Grinding paste used to adjust the fit for optimal operation

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1 comment:

  1. Einen schönen abend
    Können sie mir helfen, ich habe eine Webra 2.5s uns sie läuft nicht. Der zustand ist eigentlich gut. Der Kolben hat keine Kratzer und der Zylinder auch nicht. Er hatte nur Rauch rausgelassen und hatte 2-3 fehlzündungen, ich dachte dass er zuwenig kompression hat. Ich machte einen neuen Kolben aus Aluminium. Die obere kante des Kolbens machte ich etwa 2 hundertstel mm dicker und eine gute kannte. Läuft aber immer noch nicht. Was für ein Gemisch braucht der eigentlich? Die einen schreiben Diesel die andern schreiben sondst irgendetwas mit Ether... aber keiner schreibt das Verhältniss.
    Ich würde mich auf eine antwort freuen Lg Horath Sandro
    E-Mail: sandrohorath2000@gmail.com

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