First things first. Thanks to everyone who gave me tips and pointers on how to do this. Thanks especially to Nige for the schematic. That helped tremendously when replacing the seals as mine were so shot I count not tell which seal went first, etc. I've removed, rebuilt and replaced both track tensioners on my cat 311b in the past 10 days. All work was done by myself... no assistance whatsoever. First time took me about 5 hours. Second time took me 1 hour 36 minutes (18 minutes after I started carrying wrenches and blocking to excavator, the tensioner was out) Third time (if there is one), I think I can easily do it in less than an hour Steps: - Do NOT remove the track I learned this from a tip from Hanco. Thanks again Hanco!!). - Put a 2x4 on similar between back of big front idler (roller) and the frame to prevent roller from retracting all the way. - Back off the bolt on track tensioner, that lets grease out - Use Bucket to push back on idler to compress track tensioner - Use Bucket to pick that side of tracks well off ground. - Place appropriate safety cribbing between frame and ground as insurance in case hydraulics fail. - There are only 2 bolts holding the track tensioner in place - .... They are vertically aligned, 1 above a reinforcing metal 'rib' and one below - Reach upward through the gap between bottom track and bottom rollers, etc to remove the bottom bolt (you may even reach it through the hole where you apply grease to tighten tracks). - Reach down through hole in housing to remove the top bolt. - Tensioner is now held in place only by whatever compression is remaining on it - Bump indirectly with big hammer. It should fall out the bottom (If your tensioner is too large to fit between bottom rollers, remove one of them) - ... Alternatively, you may be able to reach through the same hole where grease zert is and twist and turn it to bring it out that hole in side (yes it will fit, at least on my 311b) - Replace seals, and re-tract tensioner all the way - Reverse the above steps, retighten the tracks and you are done (oh, don't forget to remove the 2x4) By far the most difficult part of the above for me, was repumping the tensioner full of grease with a manual grease gun. Also, if you allow your idler to come too far back (even a quarter inch), it can be a bit difficult (working alone) to get the idler to move forward enough and stay there, so that the tensioner will squeeze bak in between bulkhead and backside of spring box (the part it pushes against to tighten tracks) Respectfully Stacy Whetzell
As a followup to my track tensioner story: White Mike mentioned this in another post. Once Tracks get worn past their specs, then the track tensioner has generally reached it's maximum extension and pumping more grease results in extending the tensioner cylinder out past it's, whereupon, seals blow or are bypassed. That is what I found had happened to mine (the reason I became an expert at replacing the seals was because I was not smart enought to detect that this was the cause of the first 2 seal failures I had.) So, when I found out what was happening, I checked with Cat and sure enough, my tracks were stretched/worn way past the specification where Cat says they need to be replaced. Not having several thousand dollas with which to replace tracks, I improvised. I made me some extensions to go on the end of track tensioner so I could get more use out of tracks. Yes, my idlers are about pushed out as far as they will tolerate, but I am now hoping I can get enough wear n them that I can remove a link like White Mike mentioned, and then I might be able to run these tracks until they actually break (the bushings are in great shape).. But Cat is pretty crafty. They dont want you removing links (rather sell you new set of tracks), so they have made it so that front idler is just about run out the front of rails and still not enough slack to remove a link.... but I think I've figured out how to address that. I'll cross that bridge when I get to it. Happy digging to all Stacy Whetzell
I know this has been a long time ago, but can you tell me how you know if your tracks have stretched too much? I have a 1999 cat 311 Japan made. Thanks
If the tensioner has no more adjustment remaining (tight up against the stops in other words) and you can't achieve the specified 40-45mm of slack measured using a straight edge between the front carrier roller and the idler, then the chances are your undercarriage is worn to the point at which it requires repair/replacement.
Here is a video that explains a lot about excavator undercarriages.
Very informative video, etc. If tensioner does not hold grease, does that confirm that the track is fully extended (done for)? Machine has less that 4,000 hrs. Nearing 86, I want to figure out my options. Thx.
Not holding grease does not confirm that tracks are done for, you can have new tracks and still have leaking seals on a track tensioner. Fully extended track tensioners that leak grease may indicate track chains/rails are fully worn (As Nigel said above). In this case you will see a lot of chrome rod exposed on the tensioner, and the "axle" of the front idler will be way out past the end of the track frame.