Mark 9: Starting Carb & Cold Idle Solenoid??
 

Okay, I'm stumped.

Background: My mechanic was working on the rich mixture problem on my Mark 9, which is still wired as positive-ground. The starting carb still gets negative power from they key-switched wire, and it gets positive from an under-dash switch. The wire from the switch was disconnected, but while he was balancing the carbs, the starting carb opened up. He presumed that the starting carb must have some sort of internal short that was letting it get to ground, thus opening up. I closely examined the solenoid, and I don't see how that's possible. I noticed the plunger spring was compressed quite a bit, so I stretched the spring out and am now hoping the starting carb won't inadvertently open again. I guess we'll see on that.

But while I was working on it, a wire came off of what *appears to be* a cold idle solenoid: an electrically-operated plunger that, when energized holds the throttle open a bit (see photo). Here's my problem: I'm not aware that this car had such a device. The wire came out of it due to corrosion, and when I tried to energize the thing, it didn't work anyway. But my owner's manual has a photo of the carb setup, and there's no device like this in the picture. I thought perhaps it was aftermarket, but I can see 'LUCAS' faintly embossed in the plastic / bakelite trim, and the negative wire that should energize it is coming from the car's harness.

With the car cold, my meter is showing no voltage between this wire and the positive battery terminal. I'm getting about 9V between this wire and the negative terminal whether the car is on or off, so I figure that voltage is running through some other device and finding its way back to ground.

Can anyone confirm that this is, indeed a cold idle solenoid, whether or not it's factory for a 1960 Mark 9, and what is supposed to energize it? My wiring diagram is on its way from XKs.com, but since the owner's manual doesn't show it, I'm not holding my breath on the wiring diagram.

Thanks,
Doug

Not at my manuals right now but would suggest that is the control for releasing the anti creep device on your car (automatic right). The only other devices I have seen were stepper switches for cars equipped with AC to increase idle with the AC engaged. Since you say it is a Lucas switch I would investigate the anti creep first.

George,

Interesting. I presumed that the device was an actuator to hold the throttle down a bit. Perhaps you're correct, in that this is a passive device that loses connection to earth when the throttle is pressed by the driver, thus informing the anti-creep system to release the brake.

It turns out my rings are smoked and the engine needs to be rebuilt, so at the moment, this feels like I'm worried about carpet stains on the Titanic. But once I stop wallowing in self-pity over my beleaguered engine, I'll get back to the electrical system and see if I can prove you right. Still weird that the device doesn't appear in the owner's manual photos.

Thanks again,
Doug

Before I pulled the engine I would bull the head and inspect. With all the fuel you have been flushing down the cylinders it could be you could have a hone and new rings. Put new bearing shells in at the same time--your mech. can measure and tell.

Yeah, we figured the oil got washed out. We already replaced the valve seals with the head still on the engine, but that didn't fix anything. We then went in and inspected the cylinders through the spark plug hole with a bore camera, and two of them are scored like crazy. I honestly don't know how the compression is so good on those cylinders, why the engine runs so smoothly, and why we're not getting a ton of blow-by.

Anyway, after what we've seen, I don't see any need to pull the head off on the car; we're yanking the engine and tranny and will disassemble on the bench & rebuild the engine with z new piston set and bearings. Add a new rear main seal, new chains, valve job, and I should be good to go for another 100K miles.

Got the engine out and head removed. Oil rings have no spring left in them. Engine was clearly overheated. The block appears to be rebuildable, although there's a visible crack between 4 & 5. On this engine, there's no water jacket between the cylinders, so we're hopeful that the crack can be welded. It'll go to the machine shop in a couple of days.

What size is your engine, 3.4 or 3.8 litres ? The 3.8s had liners, so one option is to fit lipped liners to cover the crack, then skim the block face. This costs more, but the cure is more certain too.

Thanks, Fraser. It is indeed a 3.8, and it clearly has liners. The block is going to the machine shop later today, so I'll be sure to inquire about that. I've never heard of 'lipped liners' before.

DG your machine shop will have although here in the US the most often used term is a "Top Hat" liner as they resemble an old stove pipe hat turned upside down--that will cure your problem.