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Wanting info on Cat 621b scrapers

Discussion in 'Scrapers' started by Randy88, Dec 22, 2021.

  1. Questionable wizard

    Questionable wizard Well-Known Member

    Joined:
    Feb 10, 2018
    Messages:
    120
    Location:
    Ohio
    From a mechanic point of view (same for Cat or Terex equipment), I would have the air tanks cleaned (i.e, take a pic of how your lines connect to the tank, remove tank, wash out, pour in one pound of 1/4" steel ball bearings (source from McMaster Carr) and a gallon of muratic or proprionic acid (Lowe's, Home Depot), plug all holes with steel plugs, place on a one yard cement mixer and inflate a tire inner tube against it to hold it in place. Run mixer for 2-4 hours. Remove plugs carefully pointed away from you wearing PPE. Pour out contents and thoroughly rinse. Dry quickly with a torpedo heater. Pressure test. Take tank to a radiator shop that coats tanks and have the interior coated). Reinstall. Sourcing a tank to match and have all the ports in the right direction will be a challenge.

    Then I would purchase a AD-9 air drier from a truck parts shop and plumb in. Air line schematics are available. Also install a Stemco automatic drain valve in your wet tank (the first tank after the compressor or air drier). The Stemco valves really work. Alcohol inducers are a Band Aid. There is a reason you don't see OEMs using them. Sure you can get by, but solving the moisture problem is the right way for a solution. You may have a compressor that is generating oil. Air drier and drain valve will get rid of it.

    Replace your pressure protection valves with new (this is the first valve at a tank port feeding components like air shifter, seat, etc.- it shuts the accessories off if tank pressure drops too low to ensure pressure for brakes). They will have garbage in them. The Sealco ones for truck applications are inexpensive.

    I usually replace the Rotomax brake chambers on the construction equipment with 36-36 truck maxis. They handle misalignment of the operating rod without binding much better than the Rotomax, and are 25% of the price. Parking brake spring force is similar.

    If your often top loading the scrapers, switch your spill rack around so it act like a funnel so the excavator has a bigger target. Most are modified this way in NZ as they don't have as many haul trucks. The scrapers do double duty as haul trucks, plus they can spread their loads. If you want more capacity from a Terex top loading, put 12" sideboards on. Just be smart about it.

    I question whether Cat 621s being single axle drive will motivate adequately when ground conditions get soft or smeary. Here in Ohio, the JD 862s we had many years ago had to be pushed everywhere with a dozer when conditions were soft.
    Stemco auto drain (Medium).jpg Jon's phone 8-25-19 056 (Medium).jpg Thomson tandem 2.jpg Jons phone 1-16-21 023 (Medium).jpg
     
    Last edited: Dec 26, 2021
    HATCHEQUIP, John C., Tinkerer and 3 others like this.
  2. Questionable wizard

    Questionable wizard Well-Known Member

    Joined:
    Feb 10, 2018
    Messages:
    120
    Location:
    Ohio
    Jons phone 1-16-21 022 (Medium).jpg Thomson TS14G 2.jpg

    I believe a smart person can solve the Cat brake sourcing problems. We here in the US are spoiled with the manufacturer so close and we need to hone our ability to think outside our comfort zone. I don't know if Cat quit offering the air valves, or hard parts. Somebody with a thorough knowledge of air brake systems can find retrofit valves. Machine shops are available to make hard parts. Shoes or pads can be relined. Calipers can be re-bored.

    I work for a group of excavating company owners that have very little mechanical knowledge. Their answer to tired equipment is to replace with much newer. Refurbishing is out of their comfort zone and up until now, never employed anyone that demonstrated it can be done. When they rolled equipment out of their inventory, often it was a rolling disaster. They usually have a convenient case of amnesia when discussing condition with the next buyer.
     
    Last edited: Dec 26, 2021
    DMiller and colson04 like this.
  3. DMiller

    DMiller Senior Member

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    Occupation:
    Almost Retired
    Location:
    Hermann, Missouri
    Tinkerer and 59 North like this.
  4. Randy88

    Randy88 Senior Member

    Joined:
    Feb 2, 2009
    Messages:
    2,112
    Location:
    iowa
    Thanks for the replies guys, you've been very helpful, never been told or heard of the alcohol evaporator before, that goes in after the air dryer, is there anything that can be mounted before the dryer, I have one truck that the air dryer is mounted too far back and the line from the compressor to the dryer always freezes up, even though there are no low spots in it anywhere. With the service body on the truck, there was only one spot to mount the air dryer, its should be mounted about three feet farther ahead and I think the problem would not exist.

    I'm hopefully going to find out what parts cat has discontinued the next few days or so and once I actually understand the system, I can then figure out how big a deal it is.

    Coating the inside of the tanks, what do they coat them with and who would do that, I've asked about gas tanks in the past, and those need to be sent out of state and the cost is prohibitive, never heard of anyone doing it to a steel air tank before.

    As for the aluminum air tanks and getting the ports just right, we've done several, buy the new air tank, take it to my local machine shop, tell them where the ports need to be and an hour or so later, all the ports are exactly where I want them, they just weld on new ports wherever needed, do the same for stainless or aluminum fuel tanks, even used tanks. For anything pressurized, their air compressor in the shop can test anything far higher pressured than any truck compressor could ever put out, never had an issue yet with one blowing up on me. I personally like the stainless steel tanks better than the aluminum, over time aluminum will corrode really bad, especially with the liquid salt crap they spray on the roads now.

    Thanks for the link DMILLER this next week I'll order a couple of those units.
     
    DMiller likes this.
  5. DMiller

    DMiller Senior Member

    Joined:
    Feb 21, 2010
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    12,417
    Occupation:
    Almost Retired
    Location:
    Hermann, Missouri
    They were a fill and forget, usually top off after a week. Air evaporates the juice in the pot where if compressor cycles a great deal may have to look sooner. Look before start and build air or have to drain off.
     
  6. Tinkerer

    Tinkerer Senior Member

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    The shore of the illinois river USA
    Thanks for the link, Dave !
    I bought one this morning.
     
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  7. Randy88

    Randy88 Senior Member

    Joined:
    Feb 2, 2009
    Messages:
    2,112
    Location:
    iowa
    Great thing about this forum, many can benefit from any chat on here and learn something along the way and also pass on some tricks of the trade learned over the years.
     
    DMiller likes this.
  8. Oldcatpusher

    Oldcatpusher Well-Known Member

    Joined:
    May 29, 2019
    Messages:
    162
    Location:
    Arkansas
    I've had 2 621B's for 7 years. Former military machines. One came with 300hrs and 500hrs on the other. Both have over 3k hours now. Love them. Made a lot of money for me. As far as brakes I've never used them. Drop that stinger and you'll go through the front glass if the steering wheel doesn't catch you. Been on some very very steep terrain with them. I've loaded them a lot with trackhoe. They just don't go like an articulated dump truck.
     
    DMiller likes this.