Thumb Plumbing excavator thumb

[JerryCPP]

I recently got an old Komatsu PC05 mini excavator with a two-pump open system. Someone added a thumb, but I don't think the plumbing is right. They capped off the metal 3/4" main return line from the valve bank and took power from that to the thumb valve, and from that valve back to the tank, all with 3/8" hose. Now all flow is through that hose; I don't like that restriction, but it works. The main problem is the thumb is as strong as the bucket - when you curl the bucket it kills the engine. I'm thinking there should be a relief valve in the thumb's upper cylinder hose so the thumb allows the bucket to curl. Comments? Ideas?

 

[ptsg]

If I understand correctly, they used the return line to feed the thumb valve, there the main relief valve won't work properly since it can't dump the fluid directly to the tank. Basically you have no relief protection on the machine, that's why it kills the engine. Don't use the machine like that or you risk blowing the pumps.

 

[JerryCPP]

Yes, that is how it's set up, and exactly my fear. I can remove the welded-on cap that's on the return line, and make the return like it was originally, but that would eliminate the thumb, which was the main reason I bought the thing.

 

[ptsg]

If you could provide some pictures of the valves and lines. Schematic of hydraulics would also help, if you have any.

 

[dfkrug]

Yes, that is how it's set up, and exactly my fear. I can remove the welded-on cap that's on the return line, and make the return like it was originally, but that would eliminate the thumb, which was the main reason I bought the thing.

Welded on? Really?

Is your valve bank a sectional valve, or monoblock? If the former, you need to take off and repair/replace the last section in the stack with the welded-on cap. If you can find out the maker (or go to Komatsu), you should buy a replacement OUT section, and possibly a proper Power-Beyond section or PB plug/sleeve.

Whether you have either of those valve types, it is almost certainly cast steel. Welding of any kind onto that material is likely to be problematic for high pressure.

 

[JerryCPP]

I am 2 months into this thing, and am learning far more than I ever wanted to. There are no manuals, schematics, or diagrams available, and that seems to go for parts too. It was built in the late '80's, and even Komatsu only recognizes the later variants, whose manuals show a different engine, controls, and hydraulic components, so I'm on my own. This has an 8-valve bank. The two pumps feed both ends of it, a common return comes out of the middle, and goes to the tank via a 3/4" steel pipe. This pipe was cut and capped a few inches from the tank. Thumb power is taken from that pipe about 2 feet from the welded end. The thumb valve is brand new, made in Japan, and hangs by itself on the side of the machine. I contacted the thumb valve manufacturer in Japan, and the only information they give is that "Yes, we have that valve in our warehouse. How many would you like to order?" No doubt something was lost in translation. The kicker is that Komatsu uses its own special hydraulic fittings; not JIC, SAE. NPT, or JIS, so tapping in is a bit of a challenge.
Apparently this excavator was found in a swamp, made to run, painted, and, with the thumb added as the bright shiny object, exported to the U.S. and put up for auction. I won the auction, lucky me! I've not yet figured out how to add a photo, but as soon as I do, I'll post some.

 

[Takman]

I've had luck finding both parts and figuring out problems using the parts lookup from this site-> Запчасти Komatsu, бесплатный каталог, Цены online

Edit: I just checked and it does have pc05 diagrams. I couldn't find the anything about the thumb but all the control valve and line stuff is there to look at and it may help?

 

[old and tired]

...I've not yet figured out how to add a photo, but as soon as I do, I'll post some.

It's been a while but I think (since that was your 5th post) you should be able to post photos now!!!

 

[BertZegers]

I am 2 months into this thing, and am learning far more than I ever wanted to. There are no manuals, schematics, or diagrams available, and that seems to go for parts too. It was built in the late '80's, and even Komatsu only recognizes the later variants, whose manuals show a different engine, controls, and hydraulic components, so I'm on my own. This has an 8-valve bank. The two pumps feed both ends of it, a common return comes out of the middle, and goes to the tank via a 3/4" steel pipe. This pipe was cut and capped a few inches from the tank. Thumb power is taken from that pipe about 2 feet from the welded end. The thumb valve is brand new, made in Japan, and hangs by itself on the side of the machine. I contacted the thumb valve manufacturer in Japan, and the only information they give is that "Yes, we have that valve in our warehouse. How many would you like to order?" No doubt something was lost in translation. The kicker is that Komatsu uses its own special hydraulic fittings; not JIC, SAE. NPT, or JIS, so tapping in is a bit of a challenge.
Apparently this excavator was found in a swamp, made to run, painted, and, with the thumb added as the bright shiny object, exported to the U.S. and put up for auction. I won the auction, lucky me! I've not yet figured out how to add a photo, but as soon as I do, I'll post some.

On my mini excavator I have put an Adjustable Relief Valve in the hydraulic line to the thumb cylinder. I did this to restrict the forces on the thumb/bucket bushings. I have adjusted the pressure so that it still (barely) holds what I am lifting. The bucket will push back the thumb. This setup would prevent the destructive dead heading on your machine.

To plumb it in: put the Relief Valve in series with thumb cylinder, than ad a hose from relief valve to tank. Cost about $100

 

[dfkrug]

I am 2 months into this thing, and am learning far more than I ever wanted to.

So, you thought your new mini-X was gonna be turn-key, and not a project? You bought it without a test drive?

Anyway, Komatsu does have their own fittings, but you can get them at larger hyd component sellers. If you are in the US, you might try DiscountHydraulicHose online. With your 2-pump system, you are gonna have a system relief valve for each, plus some work-port RVs (aka shock RVs) associated with some of your work circuits. Your machine is old enough that it may use gear pumps and an open-center system, or it could use HST pumps (variable-piston pumps) and closed center hydraulics. How much electronic or solenoid control you have is going to determine how much you can fix without schematics.

Sounds like a fun project. I recently saw a video on Utube of an excavator being rescued from abandonment in a dense forest. Maybe yours.

 

[JerryCPP]

Thank you! I'd not found this site. I'll try the Repair Manual first, and if it is the real thing, later the Operator Manual. I've been stung in the past with so-called Model Specific manuals that were no more than general repair information, applicable to just about any machine.

 

[ptsg]

Does this make any sense to you? If you could find a serial number, so I could make sure I'm looking at the right stuff on that Russian website.

Diagram pump to valve:



Diagram Valve to Tank:



We need to confirm if the thumb valve have the Power Beyond port and the power beyond adapter for it. If it does have that, the easiest way then, is to use the pressure line of one of the pumps to feed the thumb valve. Then the thumb valve will feed the main valve through the Power beyond port with the power beyond adapter/sleeve installed. The tank line of the thumb valve, will then Tee into the original tank line.

Another solution, is to ditch completely the thumb valve. Instead, you would use a diverter valve hooked to the swing cylinder circuit (since it's not used that frequently) and use that instead.

Either way, you'll need a secondary relief valve for the thumb cylinder, on the extend port of the cylinder.

 

[JerryCPP]

I just checked out that web site. It shows up as "Not Secure" - that is, the padlock in the address line has a red slash through it. Have you used the site and trusted your credit card to it?

 

[ptsg]

I can go there easily. It does show as Insecure but still works fine. Doesn't open weird popups with dodgy stuff like some sites.

I'm just using the site to check the diagrams, I'm not buying nothing, so no, I didn't use my credit card there.

You can browse through pretty much any Komatsu machine there. You don't have to create account or put any personal stuff there, unless you want to buy the manuals.

 

[BertZegers]

A relief valve P-T-P (pressure- tank-pressure, no check valve, only relief) could be plumbed in series into either cylinder port.

On the second picture you see a connector block with plugs where the hoses connect to the pipes. I took out one of the plugs and plumbed in the relief valve. The hose on the relief valve goes to tank.
Had the block not been there, then I would have plumbed the relief valve in series where the hose connects to the pipe. It doesn't make a difference if the relief valve is in the extend or retract line, because the pressure is equal on both ports. Only the flow is opposite for extend or retract.

 

[JerryCPP]

I've had luck finding both parts and figuring out problems using the parts lookup from this site-> Запчасти Komatsu, бесплатный каталог, Цены online

Edit: I just checked and it does have pc05 diagrams. I couldn't find the anything about the thumb but all the control valve and line stuff is there to look at and it may help?

The web page I get only allows me to order shop manual or parts manual, at $99 each, for just about any Komatsu made. How did you get to look up parts without buying the parts book?

 

[ptsg]

Choose from the list on the left:



Scroll down till the PC5 shows up. I happen to choose the first one as it was the earlier ones and I didn't know the serial number.

 

[JerryCPP]

Thank you Takman - I found the site and was able to look at some information, and decided to purchase the repair manual they showed for $99.00 U.S. I ordered, paid via PayPal, and a day later got the money credited back. Apparently they didn't have the manual. I had to sign up with an email, name, and password to order. Now, I can't even look at the site without logging in, and can no longer look at the list on the left side. The directions say I must now subscribe for $99 PER MONTH! It was good while it lasted, and I do appreciate your taking the time to help me. The PC05? With what I was able to glean before the site went pay-to-look, help from you and others on this board, and many hours on line, I have the thumb problem figured out and parts coming to get it working correctly. Some day I'll go to the library or somewhere with a different web address and see if I can peek at some of those pages again.

 

[Takman]

Cool, the thumb is awesome when you need it! Not sure what's up with having to pay? I've always just gone there and used the diagrams without logging in or anything. Sorry it was like that for you.

 

[ericm979]

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