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  1. #1
    New Member
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    Sep 2012
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    Hunlockcreek, Pa
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    Komatsu D20-A, Case 580b, Ford 8n

    Default Komatsu D20-A 6 Changing sprockets

    I am about to buy a Komatsu D20-a 6 from a local private owner. Machine is in great condition accept for the drive sprockets. He has brand new complete sprockets with the centers that go with the machine. He says they are easy to change by loosing the tracks and lifting them off the sprockets, take the caps off, (I guess there is a nut that holds the sprockets on) and I can use a pry bar to remove the sprockets. Sounds easy enough to me. I will of coarse get someone to help with the lifting and also use my backhoe if needed. Does this sound right? If so, I plan to buy it. Price is $7,500.00 with sprockets, and a 12000 lb trailer to move it. What do you all think?

    A little back round on me. I have been a diesel mechanic for 30 yrs., so tools/knowledge not a problem except I never worked on a bulldozer under carriage. I live in Edison, NJ, but have 40 acres in NE Pa where I plan to work (play) with the bulldozer. Hilly terrain with lots of rocks to work on (play with).

    Thanks in advance for any help or advice you can give me!

  2. #2
    Super Member
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    Feb 2008
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    somewhere usa
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    Deere 110tlb, 4520, x749, L130

    Default Re: Komatsu D20-A 6 Changing sprockets

    Welcome to TBN elcactus,
    If you have 30 yrs experience in diesel mechanics you are way ahead of most of us here. Hope you will hang out here some and participate in the forum.

    I have had two dozers in the past and recommend you look very close at this deal. You mention the worn sprockets but how about the pins and tracks? I would think it is hard to really give the tractor a work out with worn sprockets prior to buying. Why hasn't the owner changed out the sprockets before putting the unit up for sale?

    I recommend you have someone with track/undercarriage experience look over the machine for you, it may save you alot of grief or provide you with the assurance you need to proceed with the deal.

  3. #3
    Platinum Member
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    Aug 2012
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    Hartford, SD
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    Kubota L3400F

    Default Re: Komatsu D20-A 6 Changing sprockets

    jenkinsph has given you excellent advice and I would strongly suggest you follow it. Usually when one part of the drive train is worn out and in need of repair...all the drive train is in the same condition. Replacing the sprockets is but a small piece of the pie. Track drive units can be extremely expensive to replace.

  4. #4
    Super Member
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    somewhere usa
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    Deere 110tlb, 4520, x749, L130

    Default Re: Komatsu D20-A 6 Changing sprockets

    The thing that strikes me about this machine is the small size, at 4 tons it will have limited capabilities. If I were to purchase a dozer again it would be twice that size or larger. By the time you spend the elbow grease to maintain one you need to be able to get something done.

  5. #5
    Veteran Member Dozernut's Avatar
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    South Eastern Illinois
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    Kubota L4610, ZD21, RTV900, B2630

    Default Re: Komatsu D20-A 6 Changing sprockets

    "He says they are easy to change by loosing the tracks and lifting them off the sprockets, take the caps off, (I guess there is a nut that holds the sprockets on) and I can use a pry bar to remove the sprockets."

    I have changed the sprockets on a D20 and they are anything but easy to take off. 1st the tracks with pads are very heavy, the only lifting will be with support equipment. You can break the track at the master pin, it has a dimple on it, then use your hoe to pull it off. There is a large nut under the cap you will have to remove. You will not be able to pry the sprocket off, it is press fit on a tapered splined shaft and requires a several ton puller to remove it. Komatsu makes a puller for this but you can substitute a 10 ton bottle jack to do it. Place the head of the jack on the end of the shaft, have a helper loop chain through the sprocket and over the base of the jack while you are holding it in place. Pump the jack up and you will most likely still have to hit the sproket with a 10lb sledge to get it loose. Then you will have to press the new sprocket back on.
    If the sprockets are bad the chains (the rails and rollers) are bad too. The old chains have a wear pattern that will eat the new sprockets up and you will have to do it all over again. So you are looking at new chains for the dozer. Having it tore down that far it would be best to replace the bearings on the shaft. You are looking at some major cost and labor to rebuild the under-carriage on the dozer. If it was easy and cheap the owner would have done it instead of telling you it is.

    The D20's are great little dozers and will do a surprising amount of work but I think that unless you get a very good deal on the dozer I would pass on it and look for one that the under-carriage is not worn out.
    RB

  6. #6
    Elite Member
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    Oklahoma
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    JD cut

    Default Re: Komatsu D20-A 6 Changing sprockets

    I showed up a day early to inspect a dozier, and ran into the repairman who was WELDING the pins in place on the tracks because they were worn down. The seller/owner was not there, as he was expecting me the next day. The repairman said he wouldn't buy it because this was a destructive repair and the track would not be repairable in the future.

    The lesson learned is that dozier undercarriages are expensive to repair, and if you don't know what you are looking at, you can be taken advantage of. Always take a repairman with you to look at a dozier cause they can see things you can't.

  7. #7
    Platinum Member
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    Kubota L3400F

    Default Re: Komatsu D20-A 6 Changing sprockets

    Unless you are pushing mud in unfavorable conditions...tracks are a pain in the rear and expensive to maintain. A skid steer will out perform them in most cases.

  8. #8
    New Member
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    Komatsu D20-A, Case 580b, Ford 8n

    Default Re: Komatsu D20-A 6 Changing sprockets

    Dozernut, How much $$$$ am I looking to spend on the extra parts if I change the chains, and rollers? Where is the best place to buy these? (aftermarket?) I don't mind the labor part and have the help just don't want to spend more than the machine is worth. I'm going to take my cousin to look at it. He has a lot of experience with undercarriages and is willing to help me. Just want to get some numbers together worse case. Thanks everyone for all the help. I'll keep you posted.

    Quote Originally Posted by Dozernut View Post
    "He says they are easy to change by loosing the tracks and lifting them off the sprockets, take the caps off, (I guess there is a nut that holds the sprockets on) and I can use a pry bar to remove the sprockets."

    I have changed the sprockets on a D20 and they are anything but easy to take off. 1st the tracks with pads are very heavy, the only lifting will be with support equipment. You can break the track at the master pin, it has a dimple on it, then use your hoe to pull it off. There is a large nut under the cap you will have to remove. You will not be able to pry the sprocket off, it is press fit on a tapered splined shaft and requires a several ton puller to remove it. Komatsu makes a puller for this but you can substitute a 10 ton bottle jack to do it. Place the head of the jack on the end of the shaft, have a helper loop chain through the sprocket and over the base of the jack while you are holding it in place. Pump the jack up and you will most likely still have to hit the sproket with a 10lb sledge to get it loose. Then you will have to press the new sprocket back on.
    If the sprockets are bad the chains (the rails and rollers) are bad too. The old chains have a wear pattern that will eat the new sprockets up and you will have to do it all over again. So you are looking at new chains for the dozer. Having it tore down that far it would be best to replace the bearings on the shaft. You are looking at some major cost and labor to rebuild the under-carriage on the dozer. If it was easy and cheap the owner would have done it instead of telling you it is.

    The D20's are great little dozers and will do a surprising amount of work but I think that unless you get a very good deal on the dozer I would pass on it and look for one that the under-carriage is not worn out.

  9. #9
    Veteran Member Dozernut's Avatar
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    South Eastern Illinois
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    Kubota L4610, ZD21, RTV900, B2630

    Default Re: Komatsu D20-A 6 Changing sprockets

    I am not up on current prices so the best I can do is give a guestimate.
    You will need new chains, maybe rollers, the top roller the single top roller (supports the track) between the sprocket and the front idler wheel needs to be checked. If it spins freely and has no wobble it is probably okay. The bottom rollers that keep the track in contact with the ground, there should be five, need to be checked. These are the problem rollers as they are down in the dirt and are filled with oil. If they are dry they need repair or relacement. The track adjuster is a large cylinder with a piston that you pump grease into to tighten the track needs checked, repaired or replaced. The front idler needs to be checked for bearing wear and the ridge that runs around the center needs to be a certain height to keep the track on. The yoke the front idler fits on needs to straight and unsprung and the large spring the yoke fits inside should be unbroken. The track pad bolts will need to be replaced if you pull the pads and put them on the new chains. Four bolts per pad, 38 pads if my memory serves me, times two, a lot of bolts and they don't give them away.

    I did not mean to write a book but I think I have covered the basics and I am sure I have missed a few important parts. You are looking at $10,000 plus or minus depending on where you buy parts and what you can salvage from the old parts and and other repairs that will pop up. You might try a dozer salvage yard for good used parts this could cut cost. It is not going to be cheap and you will spend more on the under-carriage then you will on the dozer and trailer. Good luck, I hope this helped a little.
    RB

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