Like Scrub I'll throw my two cents in.
IMHO you would be wasting your time going for a 9G or 9H. Anything you could find now is going to be 40 years old and pretty well Donald Ducked however well it has been looked after by previous owners. As Scrub says the rippers on the back end of the 9G/H were not Caterpillar's finest effort and hard production ripping will tear the a$$ out of those particular models. That's why back in the day we always hired in a contractor machine if we ever needed a major ripping project undertaken. "Why f**k up your own tractor when you can f**k up a contractor's machine for a very similar cost" was our motto.
My vote would be for an early (as in non-electronic) high drive D8L/N or D9L/N. The high drive has much less in the way of ripper issues than the low drive tractors. Also for the type of work you say you're wanting to do I would have thought that a single-shank fully adjustable parallelogram-type ripper would be more what you need. IMHO you can't get ground penetration with a multi-shank in that type of ground although obviously I haven't seen your ground. In 40 years I can't recall any mining dozer being equipped with a multi-shank ripper apart from coal mining operations.
If you want to know a little more about Certified Rebuilds I suggest to read this thread -
https://www.heavyequipmentforums.com/showthread.php?57973-New-CAT-D6
Despite the thread title this one may also shed some light on rebuilds -
https://www.heavyequipmentforums.com/showthread.php?34295-D5M-Blade-pivot
If you want a copy of the Ripping Handbook drop me a PM with your email address and I'll gladly send it to you.
I greatly respect your opinion, Nige as well as all the others who have shared their thoughts. May I please repeat what needs to be done:
1. I need to rip alluvial which is small rocks, gravel, sand and mud all cemented together. For this, a 3-shank ripper is the most effective and efficient.
2. I need to rip hills comprised of phyllite, quartzite, shale, schist, granodiorite and hard a$$ quartz. For that, a single shank is what I need. Fortunately, with the exception of the quartz, the rest of the country rock on the hills is geologically double-folded and fractured. If it were solid rock or granite, I'd be SOL.
Let me go a step further and discuss #1. I'm sure you gentlemen are familiar with metal detectors. Depending on the brand, they can reach anywhere from 4" down to 15" deep into the ground to detect gold. This ground does have lots of fine "picker" gold that I process through a closed-loop trommel but blessedly, much of the gold is in the form of raw pieces of gold. So the principle is simple. On the alluvial, scrape off 4", triangulate the ground and work the entire scraped surface with metal detectors - something the old timers couldn't do. Take off another 4" and repeat. For this, a 3-shank ripper going down 6-8" in the alluvium is perfect - hence, the need for a 3-shank ripper. Why not just run it all through the trommel? Because several pieces of gold have been found that exceed 10 ounces.
Now, #2. Whole different scenario. Now, we are opening up the hillside and uncovering ore deposits down in the quartz. This stuff occurs n pockets and there is no clue where the next pocket might be. A big mining company would have drilled all the hills and then take them down according to the drill intercepts. It's me, my wife and son. I can't afford the $800-1.2 million investment to drill it out. Accordingly, on goes the single ripper and you take it down 10-15 inches. Now, a similar process. You grade down 4-6 inches. You walk the ground with the metal detector looking for evidence of a pocket. The material scraped off the top goes into the closed-loop wash plant. Rocks are sent to a small primary crusher and taken down to 1-inch size. Then the broken rocks go through a sag mill and finally out onto a shaker table. It sounds far more complicated in writing than it really is in practice.
Hopefully, now you can see why we need both a 3-shank and a single-shank ripper working off a 3-shank ripper bar. Now, back to the subject.
It sounds like a G or an H is not what I need to be finding. First, the issue of the ripper coming detached is a new one on me. Of course my experience is not your experience and that is why I asked for your counsel. I started at age 14 running a gas CAT. Click the magneto, engage the crank, hold the radiator with one hand and jump off the blade onto the crank with your foot and get the ____ out of the way because it liked to kick back like a mule. Later, I ran an old 6 and then a 7 skinning logs off the mountain. They weren't old then but as I look back now - they were old. Pony motor, hand clutch, tiller (which I really liked) frictions off the deck and brakes. A wonderful experience to operate that way. So that is my "limited" experience. Well, out of high school I operated a TD24 which had no business in the woods. After a close call getting a tree fallen across the cage, I turned about, took it back down to the landing, shut 'er down and thus ended my career as a logger! Hah!
So what I've learned is to forget about a G or an H. Look for a D9 of a higher flavor - an L, an N or an R. Same with a D8. Using an excavator? Well, that defeats my purpose of taking it down a few inches at a time. If you're going to mine, I've learned there's two ways to do it. Go after it like Barrick, Newmont, Kinross, Freeport Mac or do it mom and pop. Mom and pop? That's me. One cat, one tracked loader, a backhoe, small wash plant, small mill and onto the shaker table - all done right at the point of extraction so I don't need trucks, drivers, excavator, fuel, rubber and the added capital purchase expense. Heck, the Cat might only work an hour a day - if that. The rest of the time is spent walking the ground with detectors, charging the wash plant and the crusher.
So this dozer is of tremendous importance. It is also the most expensive part of this operation. I don't have $250-400,000 to spend on a dozer and that's why I was looking at the older units. Now, I've had a reality check. I sure don't need a piece of equipment that's perpetually in sick-bay.
So I've never bought used equipment. Our skid steers and loaders were always new. What does a guy do? I can see if the chain is thin or worn uneven. I can look at the sprockets for chipped teeth or thin teeth. I can look for leaks around the finals underneath, the engine and the transmission - and I can see if the stack is blowing black most of the time not burning the fuel. But what about the engine? What about the transmission? What about these units that are covered with rust back east? The chains are rusted, the pins are rusted, the rollers and idlers rusted - how does that affect the viability of a tractor? I also know to look for a loose chain and to see how much the track adjusters are being deployed. Does all that make me an expert? No. Should I hire an expert and let that person do the looking? Probably, but they'd think I was nuts to say, "I need to buy a tractor I'm going to operate but I haven't the intelligence God gave a goose to know what to buy." First of all, the Hobbs means nothing. It may not work or it may be a new meter put in when an engine was changed. How do you know? It's not like the Hobbs in a helicopter which is documented and logged every time there is service. Service records? Duh. Most sellers don't have any. A high-hour machine that was lubed like crazy is better than a low hour machine that was neglected or abused. How do you know? Sorry to vent here but going out looking for a used cat is akin to going down town Reno and putting all my money on red. Who knows? Surely not me and that is why I joined this forum so I can get some sage advice. At least at age 70, if nothing else - I've learned to listen.
