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Old 08-12-2009, 12:11 PM
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Cavalry Cavalry is offline
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Default Jack hammer problem

I have an old IR 90lb? jack hammer. It worked pretty good and was loaned out last use. I went to use it and it seems to work as it should but does not break the concrete only chip it? I pulled it apart and made sure everything was moving freely inside.
I have plenty of air with no restrictions.

ideas...

#1 this particular concrete is very high strength ( I have no other concrete to break up right now to test)

#2 hammer is working but for whatever reason not hitting with full force.
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Old 08-12-2009, 12:59 PM
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greywynd greywynd is offline
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Rented on a couple months ago, and had the 'number 2' symptoms you have. They suspected the seals were blown, allowing enough air to 'make the action' but most just blows by, weakening the unit. Imagine blown piston rings in an engine, and you have a similar situation.
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Old 08-12-2009, 01:19 PM
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Try flooding the thing with kroil and let it sit for a bit. Last time I had trouble with my clay spade that is what was recommended by a friend and it worked great.
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Old 08-12-2009, 02:48 PM
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Cav,
Here's a subject I actually know something about
There are two things internally that will cause your problem and one external.
First, in the gooseneck where you attach the air hose, take off the fitting (probably a Chicago coupling) and check for a screen behind the fitting. It may have the neighbors lawnmower clipings in the screen, or rust.

Internally...how these things work is like this. The piston(or hammer) is driven ahead by a burst of compressor air. At the same time as it strikes the steel implement end, it has vented that air out the exhaust and kept on moving under inertia compressing some air ahead of it as it strikes the tool. Now, as there is no air behind the piston, it rebounds driven backwards by the air compressed from the front of the piston. As it travels backwards it compresses the air between itself and the Valve chest, which is a simple floating plate in a round box full of holes. The valve chest is held closed by the air compressor air behind it, til the piston arrives ramming air at greater than line pressure into the valve forcing it to momentarily open, and blast the piston ahead....now the whole scenario repeats.

Ok, sorry if you already know this. The points to look for are--the brass bushing that the piston slides through, if worn will leak the air cushion compressing in front of the piston. So without enough pressure it will rebound weakly and the piston will hardly open the valve chest behind the piston. So no power.
The other problem is crap in the valve chest. This is from no intake screen.
The valve chest comes apart in two pieces, and the shuttle inside should move freely, not sticky. You can check it before disassembly, by shaking it up and down and you can hear the shuttle inside move up and down.

One more thing. torque the side rods evenly, one tighter than the other will distort the assembly and cause it to run slow and rough.
If you loaned it out someone may have run it without a line lubricator, or used motor oil, that will cause destruction.
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