Repair of torn hydraulic cylinders
It is feared by collectors and builders of models, but sometimes it happens nonetheless: One (or even several) hydraulic cylinders is lacerated longitudinally. I think this happens when the plasticiser volatilises from the plastic and/or the cylinder is overstressed.
The result is a catastrophe in any way: On one hand, a torn cylinder doesn’t look nice, on the other hand the cylinder isn’t able to support, for example, the boom anymore.
In my case, it was the model of a Liebherr R 912 Litronic (neues Design) that I bought on eBay, where three cylinders were broken: Both cylinders supporting the boom and the at the bucket.
In order to repair such a damage, just glueing doesn’t work since the types of adhesives I tested weren’t able to bear the appearing forces, which is partly due to the fact that the face available for applying glue is only very small. So I used two different methods that I’d like to show here.
In any case it is requiered to dismount the cylinder from the model, since you can’t pull out the ram from the cylinder completely. But this is necesary since the repair take place when the cylinder is under tension.
Method 1: Sleeve
|Close-up of real machine|
|Glueing the cylinder|
|Raw, primed and painted Ring|
With this method, a sleeve is put on the front end of the cylinder. The result isn’t just made up, but the sleeve resembles the flange that can be found on real machines, were it does connect the front end of the cylinder to the body. (Also see picture of real machine, in this case a Caterpillar 325B LN.)
Despite the sleeve, it is recommended to glue the cylinder at first. Epoxy or superglue is suitable for this task. The later sould be given at least 24 hours to dry, even if the manufacturer gives much lower numbers.
Then the sleeve is made. The best way is to cut a small ring from a brass tube in the appropriate diameter. In my case, a 5,0 × 0,5 mm (~ 3/16″ × 1/64″) tube did fit quite well. This ring is primed and painted in the appropriate colour. It may be required to remove excess paint from within the ring after paint had dried. This can be done with a drill, for example.
After paint and glue are dry, the sleeve can be simply put on the cylinder (Fix the sleeve with a little glue or paint if necessary) and the cylinder re-mounted on the model.
Method 2: Carbon Fibre
|Applied carbon fiber|
If the first method seems too clumsy to you or if there’s simply not enough space (in my case, the sleeves at the main cylinders would have rubbed at the boom), you can use another method:
Builders of remote-controlled models often use so called carbon fibres when building or repairing models. These are very lightwight yet very strong fibres that can be bought on a reel for example. From this, you shuld take only very few filaments in short length. This you have to wind tightly around the damaged cylinder (The best solution would be if the resulting form resembles the flange mentioned above) and fix it with superglue in a way that the fibres are saturated with adhesive.
When the glue is dry, the the result can be simply painted.
Last but not least, I want to thank Rüdiger, who brought up the idea and also gave me some carbin fibres.