digging over drive motors

[drag1line]

Jack Deere, the drive sproket and idler sproket are BOTH slightly elevated in most excavators, not to protect them but to GREATLY smooth out the ride during travel. Mr. Hoeman, your Cat Salesman does not know what he is talking about ( What salesman does?). Per SAE J 1097, the lift charts must be calculated for 75% of stability and or 87% hydraulic capacity in the WORST conditon, which on an excavator is over the rear, for both safety and to avoid ambulence chasing lawyers. You will note this applies to the over end specification unless specifically noted different. To do differently would be dangerous and misleading.

 

[AtlasRob]

pipe in cab

Sorry about the quality, I took a pic of the pic I was shown yesterday.
The story goes that he was carrying the pipe to put it in the scrap skip. There was a length of pipe with a small piece of pipe beyond the joint. While tracking ( you all seem to say walking !) the vibration shook the small piece out of the joint which resulted in the pipe becoming unbalanced and ........
The machine is/was a 210 Volvo.

 

[JDOFMEMI]

Rob

Thats tragic. Its probably just as well the pic is not too clear. You can tell what happened, but we are spared the gory detail.

Maybe others can learn from this horrible mistake.
This just goes to show that even a "simple" task should be thought through to see all the possible outcomes before proceeding.
I am generally very carefull, and this gives me one more thing to think about when carrying things, even a short distance.


I nearly had a similar incident many years ago while clearing trees on a D-8K dozer. A 6" or so branch from a pile next to the one I was pushing whipped around my blade, and happened to be lined up perfectly with the back side of my decel pedal. I was creeping through at an idle in first gear, but when the branch pushed the pedal up, the tractor sped up. When it sped up, another branch was aimed square at me in the seat. I first tried to push down harder on the pedal, then realized what happened, and had the presence of mind to shift quickly to reverse. Had I panicked, it could have been ugly.

 

[AtlasRob]

Rob

Thats tragic. Its probably just as well the pic is not too clear. You can tell what happened, but we are spared the gory detail.

.

Sorry JDOFMEMI,I didn't make it clear ..... the operator got away with it :beatsme
He saw it coming and managed to get himself up on the seat, and saved his legs. The point was he was over his track motors ( not illegal ) and as a result the machine tracked on to the pipe more, pushing it further into the cab.
Luckly he managed to get to the key and turn it off.

 

[drag1line]

JDOFMEMI
Thanks for the pictures and I am glad that the operator survived. I pray that at LEAST ONE life is saved due to this post. I have some that I will not post who were not so luck!
Have a good one.

 

[Buckethead]

I remember an old Cat training film featuring 200 series machines where it said work over the idlers. If I remember correctly (it was a long time ago) they mentioned stability as well as wear on the undercarriage. There is no load moment indicator like on a crane to shut you down on an excavator, so if you are getting close to tipping capacity it couldn't hurt to have the weight behind you. Just my .02.

 

[D3B Dave]

I am a believer, Now.

While I have always tried to work with the drive motors behind me, for various reasons, fear of damage to the motors, more counterbalance, pulling the track tight on the bottom instead the top, and a off-beat safety reason, I never put a lot of effort in it. If in the course of working if the drive motors happen to get in front of me unless I was digging in rock I did not care.

Well the off-beat safety reason happened today. I was clearing trees from a pond dam. A lot of trees. They were close together, and ranged from 18" to 6", some dead, some live. I took out the dead ones first as I did not want any falling on my trackhoe. Careful not to push a tree over into another tree which could damage the top of a standing tree which could fall later. After 6 hours of work with just a few trees left, I squirreled around and started on a 18" tree. After a couple of root cuts I reached up a little and eased the tree over away from me. Then boom, the front window exploded, showering me with glass. I was looking at the jagged end of a branch that broke off and fell, it was aimed at my belly. It bounced off the trunk and came back through the window, part of it hit the drive levers and started driving the machine backwards. I did not flinch, I just put my heels of the pedals and kept going backwards till the branch fell out of the cab. I then picked it up with the thumb and tossed it on the fire and kept working.

The fellow that owned the property was on the other side of the pond watching. After another hour of work I was finished. I pulled up to talk to the land owner. He asked if that sort of thing happened very often. I asked why? He replied that I did not blink, just kept on working like it was normal. It was 19 degrees and what he could not see under 3 layers of clothing was me shaking.

Remember the off-beat safety reason I mentioned?. Years ago a man that I respect told me to keep the motors behind me so if any thing came through the window it would push me away and not pull me in. Tomorrow when I install the new window it will have a sticker on it for the operator to see, with one word on it. THINK

The levers are coming off the pedals, too. Just in case i forget to, THINK.

Needless to say I am now a true believer.

 

[cpfrank]

Also better to dig with sprockets at rear if something comes the front glass and hits the levers you will back out of it instead of going furher into it. The front idler system springs are there to absorb the external shock during digging also.

 

[Iron Horse]

Well , i have finally found out why you should not dig over the drive motors . Watching the Volvo factory video on YouTube , it is explained why . As the sprockets sit directly on the pins and bushes , all the digging forces and grinding actions are applied straight to the pins and bushes which causes undue wear . When digging over the idlers , all the digging forces are spread directly to the chains via the idler flanges and track rollers . Simple really when you think about it .

 

[Hendrik]

Sorry JDOFMEMI,I didn't make it clear ..... the operator got away with it :beatsme
He saw it coming and managed to get himself up on the seat, and saved his legs. The point was he was over his track motors ( not illegal ) and as a result the machine tracked on to the pipe more, pushing it further into the cab.
Luckly he managed to get to the key and turn it off.

Makes you think what would have happened if he had worn a seat belt?

 

[RonG]

Thanks,Iron Horse.I had not analyzed that far but that has to be the major reason for it.
I read it in a Cat operators manual for a 215 and figured if it would apply to Cat excavators then it might be good for them all.Ron G

 

[AtlasRob]

Makes you think what would have happened if he had worn a seat belt?

That is a very valid question.

Its one I am not going to play with as I am the worlds worst when it comes to not wearing a seatbelt when operating machines. Thats despite having a friend ejected from and killed by a Cat 988 shovel many years ago.

I would NEVER recommend an operator to not wear a seatbelt.

What I do myself is my lookout.


On edit. Thanks Iron Horse for that titbit of info.

 

[Eddiebackblade]

That is one scary picture of that Volvo Rob, I bet he'd done a fair muck shift in his 'undercrackers' when that came tumbling through the window.

I have never addded my thoughts to this digging over the motors debate, but my practice is to just dig over whatever is under me at the time.
However if I'm laying pipes or working over the edge of something, then I like to get the machine the right way around for safety.
I think all this debating digging over motors surely applies to the 20tonne plus machines on heavy applications, the average machine on a UK site is raced about everywhere with little time to worry if you are the right way around or not.
I'm not saying it's best practice, but as we all know hirers are after productivity and would not take too kindly to messing about trying to be the 'right way around'.
The one I get most annoyed at is the idiots who cannot reverse a Rubber Duck onto a low loader in the yard. Instead they drive them on steering axle first, and leave the operator with the problem! You should try reversing them off in the dark whilst carrying all the buckets with cables overhead.

 

[Bigstevex4]

may have alraedy been posted but w it has more to do with the finals acting as counter wieght when away from the work.

 

[Cmark]

I've been looking at this thread for a while and keeping out as it seems like a discussion for operators, however I thought I'd stir the pot a little from my mechanic's point of view.

I've been repairing machines for many years now and the number of collapsed excavator idlers I've replaced = lots, and the number of excavator final drives with failed hub-bearings (not counting failures due to no oil) = none, so the argument for putting less stress on the FDs doesn't really stand up.

I would say that the weight of a FD and motor wouldn't be too different from the weight of an idler and recoil assembly, so the balance theory isn't too good either.

Also, consider the situation that you are in bad ground and you are digging over your idlers. You then move along and you are now tracking hard in reverse. OH NO! Yell the purists. Mustn't do that!...Could this be a black mark for digging over the idlers?

The only good argument I've heard is the one for moving the machine away if a branch comes into the cab.

Lets all dig over the final drives and give those fragile idlers an easy life

 

[Bigstevex4]

I've been looking at this thread for a while and keeping out as it seems like a discussion for operators, however I thought I'd stir the pot a little from my mechanic's point of view.

I've been repairing machines for many years now and the number of collapsed excavator idlers I've replaced = lots, and the number of excavator final drives with failed hub-bearings (not counting failures due to no oil) = none, so the argument for putting less stress on the FDs doesn't really stand up.

I would say that the weight of a FD and motor wouldn't be too different from the weight of an idler and recoil assembly, so the balance theory isn't too good either.

Also, consider the situation that you are in bad ground and you are digging over your idlers. You then move along and you are now tracking hard in reverse. OH NO! Yell the purists. Mustn't do that!...Could this be a black mark for digging over the idlers?

The only good argument I've heard is the one for moving the machine away if a branch comes into the cab.

Lets all dig over the final drives and give those fragile idlers an easy life

A final drive motor asemmbly full of gears is alot heaver than a thin idler full of air. and also and maybe this is becuase Komatsu has so mutch power if you hit the idler with the bucket the recoil spring absorbs it the final has no such safty and you can actuly and it has happend snap a shaft or literly break the hub iin a final.

 

[ih100]

CMark, to say that because you've replaced more idlers than drive motors the idlers are fragile is like saying that because the drivers seat in a car always wears more than the passengers' it must be more fragile. If most digging is done over the idlers, they will take more punishment. If we all went to digging over the motors you'd never see an idler fail. Which would you rather replace? Idler bushes or motors/pins/bushes/final drives?

Dragline, I've never noticed the idlers or sprockets to be raised on an excavator. What types are you talking about?

 

[Cmark]

CMark, to say that because you've replaced more idlers than drive motors the idlers are fragile is like saying that because the drivers seat in a car always wears more than the passengers' it must be more fragile. If most digging is done over the idlers, they will take more punishment. If we all went to digging over the motors you'd never see an idler fail. Which would you rather replace? Idler bushes or motors/pins/bushes/final drives?

So we're suggesting that the reason final drives rarely fail is because most operators are conciencious guys who take special care not to dig over them? Hmmm? I think you'll find the reason is because final drives have big expensive ball or roller bearings in them, swimming in lots of (hopefully )regularly changed gear oil, whereas idlers have a cheap pin and bronze bush which takes all the side force when turning.

As for the myth of final drive weight, I've been working on a Cat 375 today so I did a little research. Weight of the idler and recoil assembly = 982kg, final drive assembly = 953kg. Can't say if this ratio applies to all machines but is is probably a reasonable indicator.

A recoil spring requires far more to compress it than hitting the track with the bucket. You need to be pretty determined to compress those things using the machine's own hydraulics. Believe me, I've tried doing it when the recoil spring through bolt has broken and I've needed to get some slack in the track.

All I'm saying is that in my opinion, it doesn't really matter. Operators can do far more good for an undercarriage by digging the tracks out every day, rather than sweating over which end the idlers are at.

 

[Hendrik]

All I'm saying is that in my opinion, it doesn't really matter. Operators can do far more good for an undercarriage by digging the tracks out every day, rather than sweating over which end the idlers are at.

Best thing is to keep the bucket off the tracks altogether and keep the tracks clean but we don't work in a perfect world.
Generally I dig with the blade out front and the drives out back, so I hit the blade instead of the rubber track. Also makes it easier to remember which way you are facing when moving the machine. I will dig with blade out the back if I need extra penetration power or need to level the machine on a slope. Horses for courses but they all eat oats.
And yes the story about the drives/idlers being counterweights is just that a story. Next time you are near an ex walk to the back of the machine and look at it, you should find a hefty piece of steel sitting there, it's name is counterweight. If you have to rely on the weight of the idlers/drives to counter the weight of the load you are overloading the machine and should stop doing that before you tip the thing over.
Not an ex but a good demo of when a machine has reached it's limit
http://www.skidsteersmackdown.com/season2/
go to the power lift vid

 

[AtlasRob]

.
Operators can do far more good for an undercarriage by digging the tracks out every day, rather than sweating over which end the idlers are at.

:notworthy never a truer word spoken