Cat D6D track tensioner replacement and recoil tension spring lost preload

[LCA078]

Maybe I'm not following mechanically how these pieces work with each other but it appears the stuck piston simply pushes on the thru-bolt and there are no joining mechanisms (screws, pins, insets, etc.). If so, it may be just that the piston face surface as has simply rusted/seized on the bolt end face surface. Have you tried to gently pry the piston sideways with a long screwdriver or crowbar? Otherwise, I'm struggling to understand what would hold onto the piston if the cylinder is removed. It should just "drop", right?

 

[jjdow68]

I think you need to look at pilot between coils to see if there are any cracks. Was idler slammed the whole way back? Second thing to note is compressed length is so it will fit it during assembly

I wish I knew. I’ve taken over this project from someone that passed away. All they had done was separate the tracks and taken off the track rail covers. The rest of it is where I came into the picture. I.e. what I have done so far disconnecting the idler, winching it forward, removing nuts and bolts from tension cylinder, taking sleeve out, noticing the piston not in sleeve. I’m now concerned about the pilot assembly because there is grease in between the springs as I will illustrate in this picture.
I will say this though, looking from the inside of pilot assembly, at the part I cleaned out , it looked and felt like no cracks to the housing. At least that part of it. the picture of the stuck piston is the inside of the pilot assembly. It’s the second picture attached.
‘could it have blown out the back of the pilot assembly? That something I don’t have a visual of the back side. I’ll be cleaning that up best I can and try to get a camera in there to inspect. As mentioned this looks like between a Rick and a hard place. This sucker is out in the middle of nowhere so this will have to be a field repair. the options are dwindling.
indid price a spring but not aftermarket. I was quoted 2200 bucks from cat just for the spring. ive tried to download the picture showing the grease inside the spring coil but for some darn reason the files to big. Good grief. Anywho! There is some grease back there so I suppose it’s very possible the pilot assembly is compromised in some way.

 

[jjdow68]

Maybe I'm not following mechanically how these pieces work with each other but it appears the stuck piston simply pushes on the thru-bolt and there are no joining mechanisms (screws, pins, insets, etc.). If so, it may be just that the piston face surface as has simply rusted/seized on the bolt end face surface. Have you tried to gently pry the piston sideways with a long screwdriver or crowbar? Otherwise, I'm struggling to understand what would hold onto the piston if the cylinder is removed. It should just "drop", right?

Excellent observation and you worded it better than me. I hope someone chimes in. And to your point. Yes I did try to pry side to side thinking and hoping for the same thing you mentioned. That’s why I’m thinking maybe get a washer or links of chain a welding on the end of the pin to get a better grip to pull on that sucker.

 

[jjdow68]

I think you need to look at pilot between coils to see if there are any cracks. Was idler slammed the whole way back? Second thing to note is compressed length is so it will fit it during assembly

I meant to reply to your specific and replied to the whole sorry for the misstep. But yes I will be going back to clean up the area and look for cracks. And I will have tape measure in hand for spring specs.

 

[jjdow68]

View attachment 335840View attachment 335841View attachment 335842View attachment 335843

In this last picture. Page 50 in the manual. I’m confused about the second picture from the bottom. Is that not a roller.

 

[.RC.]

Yea it looks to be an error in the manual. Your machine seems to be as it should.

Just remove the piston from the cylinder (put some compressed air in there through the grease port if it is stuck, but it would come out with a bang) that you have already removed, replace the seals and reassemble.

 

[Vetech63]

I have used grease thru the valve to push stubborn ones out.

 

[pittsburgh cat man]

Some times it takes me awhile the piston is stuck in pilot not the cylinder right. The thru bolt on back of spring push it in and see if there is space between big nut and rear pilot if you have space you could give it a wack with hammer that bolt is open to center of front pilot where piston is

 

[LCA078]

you could give it a wack with hammer that bolt is open to center of front pilot where piston is

Ahhh, the BFH method rears its head again. Hopefully Pittsburgh Cat is spot on....

 

[jjdow68]

Some times it takes me awhile the piston is stuck in pilot not the cylinder right. The thru bolt on back of spring push it in and see if there is space between big nut and rear pilot if you have space you could give it a wack with hammer that bolt is open to center of front pilot where piston is

Ok so I think I could get a decent wack on the rod on the back of the spring. if I can line it up I don’t see why that wouldn’t work. It’s tight space between the sprocket and hitting the top of that nut and rod. Would be a heck of a lot more force then prying from the inside. defi Something I’ll be checking when I’m back to the machine.

 

[LCA078]

I wonder if dirt/grime is holding the piston tight in the pilot. I don't know how much of the piston would stick out past the cylinder at max extension but I wonder if the piston just got too far out and the ramming action of the track tensioner packed dirt all around it...effectively concreting it in.

Either way, good luck with the hammer and be safe!

 

[.RC.]

Yea now I see the piston is stuck to the end of the rod. Might be a silly thing to ask. Have you stuck your hand up there and just tried to pull it off? As there is nothing really for it to stick to.

 

[jjdow68]

Yea now I see the piston is stuck to the end of the rod. Might be a silly thing to ask. Have you stuck your hand up there and just tried to pull it off? As there is nothing really for it to stick to.

Yes many times annd can budge it and I have also tried with a very small pry bar. Small pry bar , not by choice but due to being such tight quarters. Got a couple really good tugs on it from each side, left and right and got zero wiggle from that.
in the picture if you look to the back end, back of the piston, you can see some seal material that is possibly pinched to the tapper in the pilot assembly. while cleaning out the old grease I pulled a lot of seal material out of the housing. I was hoping it to be chunks of leather but it looked more synthetic or hard plastic. But was not the green seal material you see on the top of the piston. The green chunks were there but it also had that other material in there as well. my Hand barely fits in there around the pin but as you can see in the picture I was still able to reach to the back to clean all the grease out of it. That’s also when I got the chunks.

 

[pittsburgh cat man]

I'm thinking they have the wrong cage bolt in the spring there is no way the piston could get back that far with the right cage bolt

 

[Vetech63]

Better start reading the death spring thread

 

[LCA078]

I'm thinking they have the wrong cage bolt in the spring there is no way the piston could get back that far with the right cage bolt

Are you inferring that someone may have used any bolt that fit, or better yet made their own bolt, instead of buying the right one from Cat?

Say it ain't so!!!

 

[pittsburgh cat man]

Ah yep brave soles!

 

[jjdow68]

I'm thinking they have the wrong cage bolt in the spring there is no way the piston could get back that far with the right cage bolt

Interesting.

Better start reading the death spring thread

I will clean it up and take some pictures and post them up. Hopefully I can get some answers to what’s going on inside the coil of that spring. It’s a shame I’m not standing there in real time while talking to you guys.

 

[jjdow68]

Interesting.

I will clean it up and take some pictures and post them up. Hopefully I can get some answers to what’s going on inside the coil of that spring. It’s a shame I’m not standing there in real time while talking to you guys.

just read the death spring trap thread…yikes! I can tell you this I’m not gonna intentionally do something sketchy I’m thankful to this forum and everyones input. It’s given me pause and better understanding of how this tensioner and spring operates.
Not sure if the cage bolt is machined with that pecker on the end, The part that presses against the piston, or does It come in 2 pieces.

 

[pittsburgh cat man]

Cat ones are forged one piece Normaly with track adjuster out cage bolt is loose.