Free 1991 420SEL
 

I am not sure whether I should be happy or I am in for a major headache. I got this car free from a co-worker who does not want to spend anymore money on this car.

It is a 1991 420SEL with 171K miles. To date, he'd replaced the computer (4yrs ago) , rebuilt transmission (6 months ago), AC (2yrs), Radiator (2mo), Tires (3mos), sunroof, o2 sensor, battery last month and ect. Also the car was repainted a little more than a year ago. He gets so sick of the car that he does not want to deal with it anymore after recent incident.

Here is the damage. From looking at the pictures, I guess the rail or the tensioner failed and cause the timing chain to get loose and broke a piece off the valve cover. I do not think the chain is brokent because I tried to get it out but I could not. I have removed the engine but have not had the time to open it up to see the extent of the damage.

What can you tell just from looking at the pictures? Any educated guess is much appreciated. Am I better off rebuilding this engine? or just buy a used engine?

Thanks in advance.

Have you tried rotating the engine by the dampner pulley bolt with a ratchet? I too am thinking that perhaps the damage is confined to the rails and the rest of the engine is okay.

On the other hand, since the engine is out and has 171K on it, it may be wise to - at the very least - take the heads off and have them refurbished. With the heads off, you can then make a decision on what further needs to be done on the engine.

That's pretty wild! Never seen one blow out the top of the valve cover. I would guess the chain is very, very loose, How else could a piece of the rail become lodged betwen it and the cam gear which is what it looks like to me. If you are lucky you will get by pulling her all apart, new chain, guides tensioner and possibly a few gears, several new valves and of course, a new valvecover.

That's best case, I remind you. I bought a 450SL once that suffered a similar fate and the engine was ruined, water in the oil, chunks of metal in the cylinders, etc., I suspect it happened at highway speed.

Free, eh??

My bet is on a broken piece of guide rail or tensioner I would pull the valve cover, turn the motor by hand with the plugs out, and look for normal valve movement sound and action.
If the motor is already screwed, you wont make it worse by hand.. If it turns ok, remove the front covers to expose the entire chain & tensioners. If the chain has not slipped, motor might be ok. Replace the chain, rails & tensioner, drain the oil, with full oil pan removal.
Cross the fingers and try it for maybe 5 miles and drain oil again with plug this time. Stay on short intervals 500 miles or so, for a couple times to clean out oil system.
Where did the valve cover bits go...... try to find.
My .02
Ken

thanks for the advise. I will open it up and exam the damage. Xing my fingers. will keep u guys posted

Concur with Bribenz

Pull both valve covers, wiggle rocker arms.
Each one you can move with your fingers==bent valve.
Note --there could be other damage.
Pull the heads, check for cylinder scoring.
Have seen valve head break off, lodge in piston, gouge cylinder wall.
One put the con rod through the side of the block. Ugly.

9 of 10 times, however, valve job on BOTH heads(mileage) and chain and rails
gets you going.
We do them with engine in the car.
Helicoil head bolts if heads are removed(takes special jig-plate)

TxBenz,

I don't think helicoiling is a necessity, didn't have to do it on mine anyhow.

Maybe you're thinking of 3.8's?

We helicoil all cyl head bolts on M116 & M117 aluminum blocks.

Notheing like being down to #31 of 32 and heving the threads chese
when you go to final torque.

Had another one pop a head gasket 6 months after valve job--
3 of 16 bolts on that side were not tight anymore.

Lesson learned, for us,anyway.
I'm glad you have had no problem.

Thanks for the tip about helicoiling the head bolts.

What you mean about "do them with engine in the car"? The engine is already removed from the car.

late add..
 

Just to relate some 420 woes.....I have an 87 with 187000 in 8/03. Was burning qt every 500. Smoking on start up. Went to do a valve job found #1 cylinder scored from bad plug. Bought engine from MB salvage yard from same year with 107 miles. Come to find out had recient valve job. Pulled top end off old eng and dropped in new block with new TC, waterpump, motor mounts, etc. Car was reborn and does not use oil between changes and no smoke. More power all around. Was totally worth the changeout. I invested $5k in total project labor included. Have 206 on body and 110 on new powerplant. Where can you buy a car as nice as this classic for that kind of money.....So you work around your problems even if the worst happens...Take the car and evaluate all suggestions. Your enitial investment is less than mine making it worth putting a little money in to fix it.....
Later...
Dave

Project Update
 

Well, here is the damage.

Turned out that 4 of the 6 guides are either partially or completely broken. As you can see from the pictures, the broken pieces are all over. some small pieces were also found in the oil pump intake openning. Luckily there is a filter screen. Only 2 guides (lower passenger side and tensioner guide) were in tact but you can see the wear.

Driver side exhaust valves are all bent but there is no damage to valve guides, head or piston. All cylinder walls look very good.

The heads were sent out for rebuilt with 4 new exhaust valves, 8 exh. guides & all stem seals and a machine job.

Everything is now ready to be put back together and so far, total cost for parts and head rebuilt is around $1,300.

So far, here is a list of parts that will be going into this engine.
Rebuilt Heads
Timing Chain
Timing Cover O-Rings
All Timing Chain guides
Lower & Upper oil pan gaskets
Front & Rear Crankshaft seals
Intake Plenum gaskets
Throttle body gasket
Water Pump & gasket
Oil filter stand gasket
Oil pump chain rail
Timing chain tensioner and gasket
Oil filter
Upper and lower radiator hoses
Expanion tank cap
Cam oiler kits
Left and Right Head Gasket sets
Valve cover gaskets
Used valve cover

Are there anything else I should replace while I have the engine out?

More progress and pictures to come later.

Thanks for the input.

More Pics

It looks like you have it covered.

Let's see..... $1300 plus some sweat equity, and you get a car with rebuilt heads, transmission, and a/c...... not a bad deal..... and you know the heads were done right! I wish I could find such a deal!

The long, curved timing chain rail in your middle picture is an expensive part.
($40-ish from memory).
The nylon lining portion is available separately(from M-B).
It is the wear component. We replace just the lining "shoe", and re-use the aluminum base.

Saves about $35. Just a drop in the bucket, but you've got a pretty big bucket already.

Other than that, a normal parts list--
Every head gasket set I've ever bought had intake gaskets-
if you are buying sets, no need for intake gaskets.
At 187k, you might consider the rubber boots between the upper and lower intake manifold halves.
Only other suggestion would be trans ft pump seal and o-ring, while you're in there.

Enjoy.

I did purchase all the guide rails including the oil pump rail without knowing that the tensioner rail is made of alluminum base and plastic insert. Oh well.. a new tensioner rail w/insert is about $32. The head gasket sets include intake and exhaust gaskets plus some other stuff. I have quite few extra stuff and will be used on the 560 in the future if needed.

I did not purchase the intake gaskets since I know they head gasket sets include them. I did, however bought the intake plenum gaskets (rubber boots) for the upper and lower intakes.

THanks for the tip about the trans seal and o ring..

Do a good cooling system flush and put in the proper MB stuff instead of green? I second the motion for the big rubber boots between manifold halves. Another idea would be to replace all the rubber hoses around the injectors. All that stuff gets hard and leaks. Bunch of little vacumm leaks. Shame you can't easily test the injectors. When I replaced the injectors on my 560, I replaced all the little rubber hoses, the injector seats and seals, and any other vacumm pieces that looked bad or seemed inflexable. Helps on driveability. Pain to do later.

NEED HELP!!! Running into a road block putting back the cams
 

The manual instructs to turn cylinder 1 to TDC which I did (picture 1). The woodruff key on camshaft should point up (picture 2). I am confusing as to which direction UP it should be? Should it be perpendicular to the ground (pictures 3) or perpendicure to the head (pictures 4). Another question is should both woodruff keys on camshafts point up?

I only put back the chain cover and old water pump temporaty for setting the TDC.

THANKS.

Alu Block
 

I thought only 380 and 560 had Alloy blocks? We never got the 500 motor in the w126 in Oz so I don't know about it.

The 420 blocks are alloy as well.

Maybe you're thinking of the earlier 4.5 litre V8's?

BTW newr,

Looks as if you're doing an in-frame job on yours but if for any reason you end up pulling the engine, don't get the ring gear and flex plate assemblies mis-oriented upon reassembly. The engine will run like ca-ca and you will go nuts trying to figure what you screwed up on. (speaking from experience)

Chas, The engine was pulled out and thanks for the pointer regarding the flexplate and ring gear/plywheel. I removed them as one piece so there will be no mistake putting it back as they have to line up the the dowel.

Anyone else can help me with the camshaft TDC issue? I am very DESPERATE. :confused: :(

I have never paid any mind to where the woodruff key is.

Just get the cam gears on and look for the notch on the first cam tower and the mark on the cam gear, get them lined up and all is well.

sump alignment
 

Also, if you do remove the engine and take the alloy sump off it, make sure you use a straight edge when you refit to line it up with the block or it can cause vibration when it doesn't tension correctly.

Cant tell for sure on the key but if its in the correct position the cam will have no slop pushing on the #1 cyl. I know your question is only about 10-15 deg. but it should be noticable.

Yes like they said and all the vacume lines below the intake too.

The manual got me confused (yeah, blame it on the manual :)) . I think I have figured it out just like Chas had mentioned. It turns out that the timing mark on the cam is the same position as the woodruff key. There is also timing mark on the camshaft first bearing/tower which I did not pay attention. Right now, the cylinder #1 is at TDC and both camshaft timing marks line up with the bearing/tower marks so it should be good to go. I will turn the engine over by hand a few times and see if everything is in sync.

Thanks

Can you please elaborate more on this? Excuse my ignorance of the terminology, but what is the sump alignment? what is the alloy sump?

THANKS

Better to ask and do the job once eh?
When you refit the large alloy sump that allows access to the big end, make sure that the face that meets the bell housing on the transmissin is in line with the face on the engine block that meets the bell housing.
Otherwise the engine tensions incorrectly against the trans and can cause a vibration that is almost impossible to diagnose.

Got it. :thumbsup:

Project update
 

After the timing marks were all lined up (thanks for clarifying), the engine was turned over by hand a few times without interference. :). This was the hicup I had ran into so far that slowed me down waiting for clarification . I am crossing my fingers and knock on wood that I won't run into anymore problems. :). So far every nuts and bolts have been put back exactly where they came from. Thanks for the tip on this board somewhere that mentioned to lable and bag parts and nut/bolts together so reinstallation went pretty quick. Imagine if I had not done that I would be still be figuring out which bolts/nuts go where. :eek:

Attached are couple pics and the 2nd one is where I am at right now.

Update
 

The engine is now ready to go back in the car.. Wish me luck. :)

newr,

Way to go. All the best with the installation and start up!

Let us know how it goes, record an Mpeg clip so we can all hear it :D

Update - THE CAR STARTED!!
 

It was a success!!! :D I am so happy. Well, there are still some fine tunning to do but overall, it's running again. :D . I think you can tell there is a BIG grin on my face right now.. :D :D :D

The car started with only one try!!! I can't be happier. I had done many other things, but this is the first big project that I have ever taken. I spent weekends and after work hours working on this car for the last 2 months. It was a great opportunity to learn!!!.

I have driven the car for the last 2 days and put almost 200 miles on it. There is no oil or coolant leak.. :). I have not had much time to get to try everything but so far, everything seems to work except the AC which will need freon later. The 420SEL is lighter and feel lighter when drive comparing to the 560SEL. THe handling also seems better. However, it does not have the power and TORQUE comparing to the 560. The ride is very smooth. I will save the comparison later for those who are interested.

Final Cost is $1,643.45 for all parts and heads rebuilt. SWEAT not included :)

Anyway, there are 3 issues I am having right now which were not there before.

1) rough idle or engine shakes at idle which I think I've figured it out. There is a leak at the throttle body opening where it meets the air duct housing. When I spray some brake/cab cleaner, it stops and the engine smooths out which indicates a leak. The shaking is less when I put it in D and completely disappear when I step on the gas and drive. I have ordered the air duct housing. The old one is hard as rock for the metal clamp wrap around and tighten it.

2) High idle - It idles at 1000 RPM in Park or Neutral (warm or cold) and does not seem to come down when the engine warms up. It idles at 650-700 when put in Drive. The previous owner said the car did not idle at 1000 RPM when warms up. This is new. I have no idea why it's doing this. I am in the process of searching this site for clues.

3) Hydraulic Lifter noise - There is one lifter (or 2 ) on the driver side making noise at start up and seems to go away when warms up or when step on the gas. I made a mistake by did not lable the order the rocker arms and valve adjust shim (thrust washer) at each cylinder. :o

Any ideas and comments on how to solve these issues are much appreciated.

Stay tune for pictures.

high idle
 

sounds like it might be cold idle solenoid.