Komat'su PC60-7 Warm Engine, no Crank

[Mark A Weiss]

I suspect a sticking starter solenoid. Do these machines have a propensity to this problem?
The other day, I was moving some logs and while I was using my chain saw, I shut off the machine to save diesel. Five minutes later, I go back in the machine and try to start it and a faint "click click" and slight dimming of the idiot lights is all I get.
I opened up the engine bay and tried tapping on the solenoid with a small crowbar, but it still would not start. So I figured maybe I can jam the crowbar between the terminals of the solenoid and "jump start" it, but all I got was a big spark and burn craters in the end of my crowbar.
A few minutes later, I was able to start the machine normally.
Is this hot start no crank issue common on these machines? Is solenoid replacement an effective solution?

 

[Welder Dave]

Is it a Nippon Denso starter? They are known for getting arcing on the contacts and being intermittent. Drove me crazy on my skid steer. If it is there is a cover on the solenoid with 3 small screws. Take the cover off and pull the plunger out and you will see the black marks on the contacts and copper ring on the plunger. Use some sand paper or a file and clean the black off the copper. Don't use emery cloth as it could cause arcing and damage to the solenoid. Make sure not to drop the spring or other parts when taking the cover off. Probably best to do with the starter pulled out of the machine.

 

[Mark A Weiss]

This is what I have. Can you identify if it's the starter you mentioned?

 

[Welder Dave]

That looks totally different from a typical Nippon Denso starter. I think your best bet might be to pull the starter/solenoid and take it in to an auto electric shop to have checked out and repaired.

 

[Mark A Weiss]

The two bolts visible in the center photo seem to be holding the solenoid in place. If it continues to act up, I may pull it and disassemble it and see if I can determine the problem. Most likely pitted contacts.

I've had two instances last year where it didn't crank over on the first try, but then started on the second. Long time between reoccurances. I do also recall one time last year where I suspect solenoid stuck on and starter motor was running (the sound of overspeed and bearings making a racket) while the engine was running. It eventually disengaged, so I suspect this solenoid has an intermittent problem.

 

[John C.]

The extra piece of electrical gear is a safety relay. It is powered from one of the terminals on the alternator. When the engine is stopped there is no voltage on that alternator terminal. When the engine starts you get voltage on that terminal which opens the contact in that safety relay and prevents the starter from energizing. A good way to check is if when you turn the key on and the engine oil pressure light comes on in the monitor panel. If you check the terminals on the alternator, only the battery terminal post should show voltage when the key is turned on. All this doesn't mean that the starter isn't bad, it is just to make sure you change the right component.

 

[Mark A Weiss]

Logic would have it that the component with the heavy wires going to it is the solenoid.
There is a safety relay right next to the batteries on this particular machine. It's energized when the ignition is in the on position. Completely disconnects batteries when off (why can't my '05 Silverado have this--dead battery third time this year from sitting), but that's not shown in these photos. I presume you are referring to the smaller device under the larger cylinder shaped (solenoid?) device?

 

[John C.]

The thing in the battery compartment is a battery disconnect, it isn't a safety relay.

On your starter there is a component clamped between the solenoid and the starter itself which is a safety relay. It prevent you trying to start an engine that is already running.

 

[Mark A Weiss]

The little device just below the cylinder shaped object with the large cables going to it, that's the device you're referring to? Okay on the battery disconnect. That's a separate item. But the safety relay appears to be a part of the solenoid. I may be able to remove solenoid with two bolts and inspect. Starter bolt on bottom is inaccessible.