Terex RT670 Boom Drifting..?

[Nige]

I hope someone can help me with this one. An operator complaint has come down to us of "boom cylinder drifting", but does anyone know what the method is to check and measure drift of the boom, and what are the limits beyond which drift is classed as unacceptable..?

What I see is that if you park it overnight with the boom horizontal the next morning the head has come down significantly, but I don't see that as a problem. I can see no visual evidence that the boom is drifting while the crane is in operation, but then again without a specification to work to I'm pretty much in the dark.

 

[Junkyard]

Hmmm. I may be able to source a manual on it or make a call to a former customer that's a Terex dealer. Spec for acceptable drift would be a start, how bad does it let off with a load on? Does the operator have to correct it fairly often? Crane operator may shed more light than me. The old groves we had were bad about the holding valves. Probably the easiest place to start, maybe there a spec of trash in one and it's bypassing just a bit....? Let me see what I can scrounge up.

Junkyard

 

[Nige]

As far as I can see it doesn't drift at all with a load on, but that is without hanging a decent load off it and taking a tape measure to actually determine if it's drifting at all. I can do all the measuring but I really need to know if there is a spec for boom cylinder drift so that even if it is actually drifting I can determine whether or not the drift is within acceptable limits.

I get the impression that the operators are stirring the pot because, as I posted above "What I see is that if you park it overnight with the boom horizontal the next morning the head has come down significantly......" however getting hold of an operator (and especially one who speaks enough English to hold an intelligent conversation with) is somewhat like trying to plait fog .......

 

[Knepptune]

1. Call terex and get the specs. Hydraulics will drift but I can guarantee if the boom drifting down significantly overnight it's not within spec. With no load on it the crane should be able to sit for a week or two without the boom bleeding down much.

I don't know about the 670 but terex was fond of using an aluminum piston on the rod. As the piston wears out all takes it a cold morning and the boom is leaking down. Get the oil warmed up and the boom doesn't drift.

 

[Nige]

1. Call terex and get the specs. Hydraulics will drift but I can guarantee if the boom drifting down significantly overnight it's not within spec. With no load on it the crane should be able to sit for a week or two without the boom bleeding down much.

1. Not so easy when you're on a different continent ....

 

[Knepptune]

Don't know why my first paragraph is numbered.

After thinking about it I've had inspectors run the boom out 75% at a 45 degree angle and hang the hook 3 inches of the ground. If the hook touches the ground within an hour it gets a shiny red tag.

 

[crane operator]

A 670 is a pretty new crane, you shouldn't see any boom drift in that at all. I left the boom vertical on my 40 ton for 2 weeks while jacking around with my swivel, and it never moved. It's not quite like a excavator.

The easiest way to tell where your problem is: boom up to 50-60 degrees, and pull the two lines off that lead to the boom cylinder. After the initial oil runs out of the lines, look which line keeps running a small stream (and it may only be a little drip). If its coming from the "top" side- which has no holding valve, then the oil is bypassing the piston seals. If its coming out of the "bottom" side, the holding valve side- the holding valve is bad. The holding valve should lock the oil in the bottom side, with no bypassing (crane running or not, that oil should be locked in the bottom side). The holding valve requires pressure from the boom down side, to release it.

There is one other possibility. My Grove tms 300 has seen a lot of years and travel. The boom position in the rest, has worn the barrel of the cylinder. If its cold in the morning, it will not hold itself in that one position, until the oil warms up. If you boom up past horizontal, its fine. Your terex hasn't seen that many years, but it may have had some rough travel, on and off the boat, chained down and rough lowboy travel to wherever you are. It may have a damaged piston or barrel, or holding valve from rough travel. I would see if it drifts in all positions overnight. More than 2-5 degrees overnight would be unacceptable to me on a crane that new. If its drifting that much with no load, its drifting with a load.

For a test, I would find something 30,000- 40,000 lbs, boom out 60-70' of stick (20' radius or so) and pick it up. Hold it 6" off the ground, it should stay there for at least a couple hours without moving more than a inch or so. If it's moving down, and on the ground in 10-15 minutes, you've got problems.

 

[crane operator]

The only boom drift you should see in the crane overnight, no load, would be the expansion/ contraction difference in the hydraulic oil from temperature change. The oil is 200deg operating temp, locked in the bottom of the cylinder at the end of shift by the holding valve. As that oil cools it gets a little smaller. a lot smaller if its 20 below the next morning. Moving the boom a few degrees.

You shouldn't leave at end of shift at 45 degree boom angle and come back to 10 degrees the next morning.

 

[DK88]

gotta watch pulling the hoses off, its unknown if the holding valve is stuck and its the c/v keeping the boom in the air.
imo there should be no drift on a boom..
ive had rotating joints out of many link belts and the boom has never moved even over a week or 2