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Friday, January 25, 2013

Reseal of Boom Lift Cylinder from a Kobelco Excavator

We have been offering a hydraulic cylinder reseal and rebuild service for about three years now and we thought we would write about a particularly tough job we had in this week. 

Cylinders on earth moving equipment are designed to be STRONG and to work in the worst conditions imaginable, that is, in dirt, rocks, dust and mud and at pressures up to 270 BAR (4000 PSI).  So most cylinders will only come apart if you are equipped with all the special and necessary tools required to literally force these components apart.

This particular cylinder was off a 7 ton Kobelco excavator it had  completed about 4000 hours of work, it had a 100 mm Bore, 850 mm Stroke and 55mm Rod diameter.

Generally there are 2 parts where a large Force is required to dismantle a Hydraulic cylinder.

1. Unscrewing the Gland nut on the end of the cylinder. These usually come apart .... eventually with the use of a correctly sized "C" spanner (or Pinned Cam tool) and a long bar for leverage.
The exception are some Yanmar Cylinders that are made to such close tolerances that the threads usually seize or bind up after a turn or two, .... then... liberal amounts of heat (enough heat to usually melt the seals!) and lots force are required to unscrew them.

 2. Unscrewing the nut that holds the Piston onto the Piston Rod.
These nuts are usually done up extremely tight as the piston is the component that has very large forces acting on it in alternating directions of each in/out cycle of the cylinder.

On the Kobelco cylinder despite all our efforts (including heat) we could not undo the nut. The 300 KG steel bench was flexing and creaking under the strain! We could apply more force but we knew the bench could not handle it and would flip or tip over under the high torque we would need to apply. Bolting the bench to the floor was not an option as its construction was designed for weight not for large twisting forces.
Time was now a critical factor as the customer was picking up the cylinder the next day, So we quickly bolted a 2 meter long steel beam to the concrete floor and then bolted a 200 mm steel vise to it.   
We then tried again and our floor mounted beam and vice worked a treat!
By our calculations we applied around 4500 NM (3300 foot pounds) of torque to the nut before it came loose.  To put it into comparison the typical torque spec to properly seat a crankshaft balancer on the Chev LS1 V8 engine is 330 NM (240 foot pounds) of torque.
Cheers and all the best for 2013 !
From the team at Mobile HoseFixers and Hydraulics,
"Living the Dream" on the sunny Gold Coast of Australia.