Free 1991 420SEL - PeachParts Mercedes-Benz Forum

newr · #1 01-07-2005, 04:43 PM

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.

Kestas · #2 01-07-2005, 08:13 PM

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.

126nut · #3 01-07-2005, 09:07 PM

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??

ken_xman · #4 01-08-2005, 08:16 AM

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

newr · #5 01-09-2005, 03:45 AM

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

Tx Benz · #6 01-09-2005, 01:27 PM

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)

126nut · #7 01-09-2005, 05:55 PM

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?

Tx Benz · #8 01-09-2005, 09:51 PM

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.

newr · #9 01-10-2005, 01:52 AM

Quote:

Originally Posted by Tx Benz

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)

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.

Dave Bunker · #10 01-11-2005, 11:23 AM

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

newr · #11 02-05-2005, 04:15 PM

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.

newr · #12 02-05-2005, 04:20 PM

More Pics

Kestas · #13 02-05-2005, 08:07 PM

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!

Tx Benz · #14 02-05-2005, 09:44 PM

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.

newr · #15 02-06-2005, 11:50 AM

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..

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