Engine locking up while vehicle is not running? How can this be???

[meporsche]

Head scratcher:
2010 Honda Pilot, 150K. Vehicle was last driven while everything was normal, oil pressure, temps. no fluids in oil pan that shouldn't be there, just oil. Parked for 1-1/2 weeks, attempted start, battery dead. Charged battery, click click, cables hot. Relaced cables, grounds, starter & battery. Click Click. Pulled starter and it tested fine. Could turn engine with socket wrench on upper pulley bolt, difficult but plugs in. After a month, gave up and had it towed to a shop.
Told me the new starter was bad and he would put in another. He did. Click, click. No surprise. He pulled plugs, turned over engine by hand, turns but very hard. Put PB Blaster in cyliders and let it sit for a few days. No improvement. His diagnosis is that engine is going away/gone, too tight. Timing belt intact or valves would impact pistons when turning by hand.
Says trans/torque converter not the problem. New engine needed he says. Sounds like bullsh*t but the fact is the damn thing won't trun over
How the bloody h*ll does an engine tighten up to the point where it can't be turned with a starter? While it was sitting in the driveway? If I believe this guy, the vehicle is basically trash since the cost of swapping in another engine is prohibitive on a $10K car.
Has anyone EVER heard of such a thing? I haven't and I've been doing my own mechanical work for 40+ years including overhauls.

Keep in mind while reading this that the engine was running normally when shut off, had been idling smoothly while I unhooked my utility trailer then backed up to the garage and shut it off. THE ENGINE HAS NOT TURNED A REVOLUTION SINCE WITHOUT THE AID OF A SOCKET AND BAR.
Tearing my hair out here. I don't want to throw good money after bad but I hate to give up on a really nice, formerly reliable vehicle.
Cross posted on Honda Forum.

Thanks to ANYONE that has ANY ideas.

[Stealthee]

The mechanic is full of shit. It could be something as simple as poor grounds or a poor signal to the starter.

[tomj76]

I wouldn't signoff on a terminal condition without double checking.

Option 1: DIY, take out all the plugs, turn crankshaft by hand wrench while making sure the camshaft is turning (maybe remove the valve cover), This should require less than 20 ftlb of torque.

Remove belts to be sure it isn`t the PS pump, A/C compressor or even a bad pully.

Look for and eliminate any other external drag/friction that could cause this. Consider that a bad pully or other hangup on the serpentine and/or timing belt belt could cause this.

Option 2: Take it to a shop that specializes in engine repair and let them diagnose it. If it's a good shop, they will quickly get to the real cause.

[maxwedge]

I saw this happen on a Toyota, the ac compressor seized.

[tomj76]

I'm wondering if you have made any progress. I saw on your other thread that you have previously turned the crankshaft with a wrench. You might want to measure the torque required to get the crankshaft to turn and post it here.

DC motors (such as starters) have maximum torque when they are stalled that drops as the RPM of the motor increases. I've read that the stalled torque is 3-4x higher than the torque once the engine is cranking, and an engine with plugs might need as much 150 ft-lb of torque on the crankshaft to get it turning, but only 50 ft-lb to keep it turning at 100 rpm (engine). Starters are often geared down by 10:1, so the torque from the motor only needs to be 1/10 of the crankshaft torque.

I've also read that newly rebuilt (still on the bench) turning torque of crankshaft and pistons (without valves) is ~30 ft-lb, but this drops after break in of the rings. Also, adding the camshaft(s) torque is significant (which I forgot to consider when I told you 20 ft-lb) since the camshaft lobes push against the springs, based on the profile of the lobe, tension on the spring...

[meporsche]

Here's the latest, sending out an oil sample for possible vandal contamination. Engine can be turned with a great deal of effort with an 18" ratcheting bar. With plugs out. there is a "hard" spot in the revolution where it is more difficult to turn. Still no idea

[maxwedge]

Pull the pan and look at the bearings and oil contamination, that will tell the story.

[tomj76]

I agree, or take the camshaft out of the test by removing the timing belt and loosen the bearing blocks to allow all the valves to release, then turn the crank without the spark plugs.