300SDL Stuck engine with bad noise and vibration when cranking.
 

1987 300SDL 200,000 miles

Hello everyone. The mighty SDL has suddenly sprung a frightening set of symptoms, out of the blue. The car ran normally on a 15-mile freeway and surface street trip in the morning. When I tried to start it mid day it made a loud unusual grinding noise and vibrated terribly when I started to crank it. It rocked the whole engine severely and sounded like something was grinding itself up. The serpentine belt, which had probably less than 10,000 on it suddenly has shredding on the edge that I had never seen before.

I had someone crank the engine while I looked at the belt. Cranking the starter made the huge noise and vibrated the engine (one or two cranks, then he stopped), but I also saw that the serpentine belt rocked slightly during the cranking, but stayed in place, perhaps getting a bit more edge shredding.

I removed the serpentine belt to see if the AC compressor was seized, but it and all other devices rotated normally. The same cranking symptoms persisted with no serpentine belt installed.

I pulled the starter and tested it in a vise. It seems fine; spins with lots of power and the solenoid pushes the gear out like it should. I don't know if there's anything else to test for, but I could tell from the original symptoms that the starter motor had plenty of torque, because it shook the engine like crazy.

Flywheel teeth looked perfect.

I inched the flywheel around at least a 1/8 of a turn with a screwdriver in the teeth, and it gave about as much resistance as you would expect a big motor to give in that situation.

Does anyone have any ideas about this?

Many thanks
Bruce S

Timing chain or oil pump chain let go causing valve collisions, or vacuum pump?

What if you turn the crank by hand using w/27mm socket wrench?

Strange. Pull the valve cover and turn the engine by hand to check cam timing.

Sixto
87 300D

Turned the crank
 

Hello again,
I turned the crankshaft with the front bolt. It rotates approx. 1 1/2 to to 2 revolutions in either direction; then it's stuck. It doesn't clank to a stop, but rather gets very hard to turn, like a soft but firm stop. Any guesses as to what's seized or broken? It sounds like I might be looking for the pumps or chains, as you suggested. In spite of trying three different digital service manuals, I still don't have a proper exploded view of the engine to ID or r/r the pumps or the chains. I could just drain the oil and start looking. Any ideas what I'd be looking FOR?

Many thanks!
Bruce

never turn the engine backward, you can cause the timing chain to slip...

Well remove the valve pan and have a look. The lower block sounds okay.

While generally a bad idea its not going to slip. Engines are designed to rock backwards a bit, anyone with a stick shift knows that.

Is the noise from the front or back of the engine?

did you perchance have a look at your timing chain? if it's broke you might have some Valves open and the pistons hitting them..

Was the cam turning with the crank?

Your engine has an extension to the oil pan that can be removed without much difficulty (drain the oil first!). Remove the extension and see if there's anything other than a film of oil in the oil pan. Check the drained oil, too.

This is what's going on behind that front cover -

http://www.w124performance.com/image...ront_view1.jpg

Sixto
87 300D

Maybe Vacuum Pump Failure?
 

Might want to pull the vacuum pump. Maybe the bearing case came apart or maybe the bearing arm broke off ---parts in the timing chain area, etc?

Wow! cool pic Sixto, I wondered what in looked like inside there. Keep us posted Audible, I'm curious to find out what happened.

Back to the problem
 

First, many thanks for the replies, and the cool timing chain pic.

Finally just got back to the car after a couple months delay (!).

I drained the oil and removed the oil pan extension; no metal or bits of anything wrong in there.

I also removed the valve cover and tried turning the engine by hand again while looking at the chain and the cam. I swear to God I'm not crazy, and it WAS stuck, but this time I turned the engine about 5 complete revolutions of the bolt on the end of the crankshaft, and nothing stuck! The chain looked perfect as it went around the cam gear, and was snug with very little free play. I didn't check the cam timing yet, mostly because I don't know how and knowing me it will take about two hours for me to figure it out. But the cam timing was fine when I drove the car last, before the engine stuck, and I don't see any damage or anything I'd associate with it slipping.

Since it really WAS stuck, it doesn't seem like a good idea to just put it back together without finding what did it. but with everything looking fine, the only thing I can think of is to pull off all the chain covers and look inside. I suppose I could also put the starter back on and see how that works.

That's my story and I'm sticking to it. Ideas gratefully accepted!

thanks
Bruce S

Does your engine lose coolant or smoke? I had similar problem with my SDL, starter spin but stuck dead. Could not turn the engine by hand with a socket. I removed the injector and turned the motor by hand, coolant squirt out from the injector holes. The engine was hydo locked in my case, coolant leaked thru the head gasket.

Not a bad thing to consider as a possibility. Over the time sitting the coolant could have leaked pass the rings.This would make the engine free again. Check your oil carefully as you do not want to start that engine if there is anti freeze in the oil. If you cannot determine one way or another sending the oil out to find out if there is anti freeze in it might be money well spent. Is your radiator down quite a bit?