Komatsu PC-400-8 Slow working equipment

[ejuan]

Hy guys. Im experiencing problems with a PC-400-8 working equpiment. It is lacking force and has really slow movement. When the problem started the arm cilinder also started drifting automatically when you let of the leveler. Im guessing problems on the main valve maybe there is a stuck spool or something or the arm relief valve could be letting all the oil go to tank. Any ideas guys? Help will be aprecciated.

Juan

 

[John C.]

Any codes, how many hours and what size bucket or what kind of attachment do are you using?

 

[ejuan]

Machine is displaying no codes... thats why it giving me a headache. I measured pressures today at both of the pumps and they are below standard value indicated by shop manual. Machine is not able to raise a load. It just stays static when you load it. Today I checked both relief valves at the main valve and they looked ok. Also adjusted them the most i could but there was not a change on relief pressure... Only weird thing is that the arm cilynder started drifting when this problem started showing... maybe the arm spool has a problem? As I mentioned before... Help will be really aprecciated.

 

[John C.]

It sounds like the pressure compensated lift check is stuck on the arm cylinder letting load sense pressure bleed off. There were plenty of problems with these on the Dash 6 machines. I haven't worked on the Dash 8 machines and am not familiar with the main control valves. If you have a book for that machine it will explain what those valves do. Basically they are a standard lift check that gets pressure on one side from pump flow when a circuit is run. The other side of check valve gets pressure from all the other circuits. That way any low pressure circuit doesn't rob flow from a high pressure circuit being used at the same time.

At any rate you would probably be ahead with someone from the dealer who has been through this problem before.

Good Luck

 

[ejuan]

Thanks for your help. Shop manual indicates it has 3 of these compensation valves for the arm cylinder. One for arm out, one for arm in and other one for arm HI in (Wich I dont have an idea what it is for). I Should check all of them right John? Are they intercheangeable?

Thanks.

 

[John C.]

There are two spool valves to work the arm and the boom. Arm HI is just the second valve that is fed from the opposite pump. You can try buying one valve and swapping it with each other unit until you find the bad one but there may be more than one bad one. Those valves are expensive so that is why I suggested finding someone with some experience as there could be other problems.

Generally, when the dealer saw a problem like that, they just replaced all the compensators and some times that wasn't the problem at all.

 

[ejuan]

Do you think this might be the problem? Apparently this is the HI Arm compensator valve. Thanks so much for your help, you nailed it. Any other steps I should take beyond replacing the compensator, filtering the oil and changing filters?

 

[John C.]

Wow, I've never seen one break like that. Nice catch. It looks like you got the pieces also. Now I would be a bit suspicious of something wrong in the stick cylinder. You might ask if it was drifting down on its own before the problem.

I would definitely pull the suction strainer out of the tank and look for pieces stuck on the screen. Making sure the load sense lines and fittings going back to the pump probably should be pulled and blown out with air pressure also.

Looks like you are well on your way to being a top line Komatsu wrench.

Congrats!

 

[ejuan]

Thanks John! Your help was more than useful... The mechanic is already cleaning the Hydraulic tank and we are going to change the hydraulic filter. I'm pretty shure it wasnt drifting, but machine started slowing down until one day it wouldnt work no more. Machine is only 4000 hours. Do you think the arm cylinder should be dissasembled for analysis then?

 

[John C.]

I'm thinking that I would probably put the machine back together and try it out for awhile. My thoughts on the stick cylinder are tied with why did that spool breakup so bad. Komatsu isn't known for material or machining failures like that.

Good Luck!

 

[ejuan]

I'll let you know how does this end John. By now we´re waiting for spares.

Thanks for your kind help.

 

[Dr Komatsu]

There is a parts & service news on this subject, you need to check internally that area the compenator seat in in not damaged or ovalized if this is the case then the valve slice needs replaced, if not there is now a one piece compensator assy that replaces the 2 piece one shown in the picture, the part number for this is included in the PSN .

 

[ejuan]

There is a parts & service news on this subject, you need to check internally that area the compenator seat in in not damaged or ovalized if this is the case then the valve slice needs replaced, if not there is now a one piece compensator assy that replaces the 2 piece one shown in the picture, the part number for this is included in the PSN .

Actually the valve seat got damaged. We are looking for the slice but is not sold as a separare part according to spare parts manual :beatsme. Dealer is helping us with that.

 

[jey_c]

Beautifull story, but I think the price is not cheap at all if you want to change all the Hi valve body, anyway good luck

 

[ejuan]

Beautifull story, but I think the price is not cheap at all if you want to change all the Hi valve body, anyway good luck

I know this is not going to be cheap at all. If any of you guys could give me a clue on why this could have happened or the posible causes I would aprecciate it. I'm sure my boss is going to start asking for the reason why this component failed the way it did when he knows the price of the spare parts.

 

[John C.]

The first issue is damage from tramp steel off some other part such as the stick cylinder. The other two issues concern design and manufacturing defect. The fact that Komatsu has a bulletin out on just this topic is more than a coincidence and pretty much confirms defects in design and manufacturing. If you purchased this machine new from the dealer, I would suggest trying to shame the dealer into some kind of help with the parts. Should that not work I would contact the factory sales rep for your area and try to find out if there is some kind of coverage from the factory that the dealer isn't letting you know about. You can always play up how you like the machine and the people but the bottom line will decide what the next purchase will be.

If you bought the machine used, pay up and get it running again as soon as possible. Get to be friends with the dealer and factory people if possible and set them up for a hard campaign when you decide to purchase the next machine. This failure should provide at least a little bit of leverage down the road.

Good Luck!