A number of things could happen when the chain breaks. First off, when the break happens the camshaft no longer turns which means the valves are stuck in their present position. However, the crankshaft continues to turn which means the pistons come up and hit the valves, bending them and also may punch holes in the piston crowns. Also, that sudden force on the pistions could bend (or break) the connecting rods, transferring that force down to the crankshaft and possibly causing damage there also. So bent valves may be the least amount of damage. There are other chain reactions going on throughout the system that I may not even have touched on here. All of these things may or may not happen. But you did ask for worst case.

 

I've wondered about this also; the way I see it, it could go like this, from best case to worst:

1. The valves don't get bent through absolute luck.
2. The valves get bent.
3. 2, and The cam(s) is/are broken.
4. 2,3, and the cam bearings are pulled out of the heads.
5. 2,3,4 and the pistons get smacked (dented)
6. 2,3,4,5 and one or more gets holed.
7. 2,3,4,5,6 and the connecting rod(s) or crank is damaged.

I suppose if such a car turned up in my driveway, I'd HAVE to get into it to find out if it was fixable. Problem is, I'd have to invest a lot of time and probably low four figures in gaskets and valve jobs alone to find out if there was any damage within the block itself.

Scenario #1 is so rare (but it HAS happened...) but take a look at #2. Are the cams still straight? Are they weakened internally so that they will go unexpectedly in the future? Are they bent just a little so that there will be a future cam bearing failure?

#2 is bad, Then there is the matter of crossing your fingers on getting the heads on again without helicoiling - it would take a special tool and probably a few hundred$ of helicoils to do this job right. Even after all that, that engine might go 200,000 miles well maintained, or 200 - just no way of knowing without a complete tear down and measurements with equipment I don't have, in which case you might as well get a different/rebuilt engine.

If it were as easy to remove/install the intake/exhaust manifolds and heads as with a carburated small-block Chevy, and if a "head set" of gaskets could be had for $50, maybe the story would be different and more people would look into this.

 

Believe me when I tell you there is no such thing as a cheap fix when the timing chain breaks.My neighbor had a 1975 SL and his chain broke and bent some valves,connecting rods and pistons.It cost him about $3500 to fix everything.It would have been much cheaper for him to have had the timing chain and guides and tensioner replaced according to recommended maintenence.He didn't do it and it cost him big time.

 

Believe me when I tell you there is no such thing as a cheap fix when the timing chain breaks.My neighbor had a 1975 SL and his chain broke and bent some valves,connecting rods and pistons.It cost him about $3500 to fix everything.

1. A consensus seems to be building suggestion at least one possibility is bent rods. I can certainly visualize how that 'might' occur. I've been "lucky" enough to see a 380 bent rod and diagnose the cause, so...it's very hard for me to believe this would be an outcome of a chain failure. Obviously the rod is in the direct line of fire, and the neighbor above may have had a rod involved in the repair, but you're sure one actually bent? Thanks.

2. Since you brought up the money question, I'll play devils advocate: Frankly, a $3,500 "rebuild" by a third party doesn't seem that outrageous if one looks at other forum threads and postings discussing the costs of rebuilding. So...an engine with 150,000 miles might be a candidate for a rebuild; and, one with a chain break certainly would...what's the difference in costs?

Thanks, guys. Dave

-engr693: you have a current cylinder index of 37...I think I see, but why an odd #?
-strife2: aha! everyone would EXPECT bent valves but maybe not! Right! Tell me more about the need for helicoils, lots of them...I have a day off today and my brain is obviously elsewhere.

 

Tell me more about the need for helicoils, lots of them...I have a day off today and my brain is obviously elsewhere.

In theory, the aluminum block engines require helicoils to hold the replacement head bolts. Some folks clain they can make do without 'em.

Perhaps this is another reason the old iron block V8 in the 450SL is considered "bulletproof" in comparison to the later engines. (But it will still suffer the same damage in the event of a timing chain failure.)

 

Dave, odd cylinder index count in one word....



Weedwacker

 

In theory, the aluminum block engines require helicoils to hold the replacement head bolts. Some folks clain they can make do without 'em.

Occasionally the guide plates for this are available on eBay (really, really expensive); I seem to recall that the guides are deliberately misaligned by a degree or so! I was interested in this because, well, someday, I'll need a valve job and it's a big gamble to see if the head bolts would hold. If it doesn't work, you are out a lot of $$$$ in gaskets and maybe a lot worse than that.

Apparently, if you are lucky and skilled with a torque wrench and "the touch", head replacement can be done without helicoiling.

 

The timing chain broke on my '84 380SL when the previous owner had it and the damage was so catastrophic (estimate from the MB dealer was $6500) that he decided to bite the bullet and get the entire engine replaced with an MB factory rebuilt engine.

I've never had one break on me and I had a friend that worked on Mercedes-Benz for 40 years and said that he'd never had one break, but I feel like that I just can't take the chance. I have them replaced every 100K. The one on my S500 was $1200 (with guides and tensioner) but a new engine would be upwards of $12,000.

Good insurance for the money I think!

 

Chain break

The engine in my 79SL came from a SLC (I think) and even it has heli-arc weld marks on the left valve cover. Previous oner had guide break and bent valves. He redid the valves and menchioned chain. I read a few mesages in here about the timing chain and did not hesitate.

And now that I have the odometer working again I'll know when to do it again.

 

Here's my 2 experiences:

Mom's POS Mercury Van: Timing belt went out - nothing happened - $135.00 repair

Brother's and my old project: 68 Camero, Just shy of 700 Hp, 9.03 1/4 mile - I was stationed overseas. Came back to 3 screwed valves, broken connecting rod which allowed the Piston to smack straight into the head. He was est. at 165+ when this happened. Never ran the same.

From what my normal mechanic told me, newer cars usually don't have catastrophic outcomes from a belt/chain breaking.

 

Bent Valves

From what my normal mechanic told me, newer cars usually don't have catastrophic outcomes from a belt/chain breaking.

They are called non-conflict engines. Once you get the compression ratio up there then the space between the top of the combustion chamber and the top of the piston gets very small and there is no longer enough room for the valves to be extended and the piston to be top dead center. You get conflict.

 

Well, it depends on the design of the engine, whether or not it is an "interference" or "non-interference" design. A non-interference design has no possible position of crank/timing that can cause a valve and piston to meet. I think it is safe to say that GENERALLY, low-performance engines are more likely to be non-interference. Case in point; the absolute POS 1.8L Brazillian engines in 1980's era GM cars (I had 3). I got so good at changing the timing belts on these after failure that I once did it on the side of a road under extremely trying weather conditions (a tornado wiped out a good part of a city about 8 miles south of where I was while I replaced the belt).

 

??

I thought that was what I said?

Ford Ranger $22.00 timing belt. 30 min change. Non- conflict engine, at least the four cylinder.
Ford Pinto $36.00 belt. 30 min change. Non conflict
450SL $130 chain first time 115 min Change. Conflict
Masda truck
Courier
Chevy 454 in an Airstream Clasic motorhome. That was a monster to work on.

These are the vehicles I have put a timing chain / belt on.

 

Noeljb........Sounds like the story of my life...Never owned a new vehicule...always bought $500-$1500 beaters. I too learned how to change belts/chains......and rads...starters.....waterpumps...etc...etc... Always in the rain or on the coldest day of the year (up here in the great white north).

 

Hey... I'm with you guys. When I was 16 I was told that I had to change the Freeze Plug on the old Monte Carlo if I wanted to borrow the car.

I had no idea what a Freeze Plug was, but with the hormones of a 16 year old, I found out what it was and changed the damn thing within a couple of hours.

(No score, by the way..... but the car got fixed)

 

Freeze Plug

Hey... I'm with you guys. When I was 16 I was told that I had to change the Freeze Plug on the old Monte Carlo if I wanted to borrow the car.

I had no idea what a Freeze Plug was, but with the hormones of a 16 year old, I found out what it was and changed the damn thing within a couple of hours.

(No score, by the way..... but the car got fixed)

And have you see where they put two of them on a dodge truck? Got to pull the transmission just to see them clearly. I like my truck, I don't like working on it.

You should have seen me at 12 fighting rear wheel skirts on a GranPrix.
Mom couldn't change that tire in the rain.

All that a Degree in Entomology and I learned how to use a periscopic sextant at 7 mile a minute.

Won a war too!

BORAH!

Oh and sorry about you not scoring.

 

Thanks for posing this question about timing chain breaks. My 380 SL is my first MB experience and I'm a bit overwhelmed just yet. I'm impressed with the quality and design of these machines but like anything new I worry about the things that I don't understand well. When mine was running I had heard some chain slap during startup and I started worrying (I'm at 110K). This thread has opened my eyes.

Regards

 

If you are hearing slap I'd change everything out yesterday.

More often than not @ this point I see more timing rail failure causing timing to jump then outright chain failure.
Usually piece of a broken rail makes it's way b/w the timing gear and chain..after that it gets ugly.

As for helicoiling, chances are if your car is pre 88/89 it will need it.. If the car has been overheated it will Definitely require HC's.

You can check if your threads will hold prior to R&R'ing the heads by backing the bolts off a touch and re-torquing. Touch or no touch, if the threads won't hold the requisite touch your up a creek.

The guide plate for drilling/tapping runs about 500$ last I checked and is Necessary to get the angle of the bolt holes/threads correct.

On today's docket is a full chain/guiderail/tensioner swap on a 1990 560SEC.. 85K but I Do not trust nearly 20 year old plastic;-)

Jonathan

 

Jonathan is right - if it is slapping, it's about to fail. The primary failure mode here is NOT the chain breaking, it is once of the four plastic upper chain guides getting brittle with age and heat, then failing. As Jonathan said, a piece of that guide will follow the chain up to the cam gear and, thanks to the amount of chain stretch allowed by the chain tensioner mechanism, be pulled through the cam gear for 1/2 of a revolution. That normally allows the cam gear to slip timing, which WILL result in V8 engine valves hitting the pistons. Something will break or bend (or both) at that point and it just got expensive.

If you pull your valve cover, take a look at those plastic chain guides. If they're a deep maroon color rather than the new milky white color, it's time.

 

this just had to be added
Convert Timing Chain to dual – 380SL

 

I know this is an old thread but having heard the fatal slap at start up I know I dodged a bullet. Thanks to members here and internet search.

 

Just aquick comment. I bought a used,one owner ,'84 380sl two years ago. I received all the maintaince records from the date of delivery. It had 148,000 miles on it when I bought it. According to the records a timing chain broke and seized up the engine at 78,000 miles. Total repair cost was over $8000.00 including a new factory short block. I was so afraid the this would happen again that I had the chain replaced at 153,00 miles. Cost was under $900.00 all. New chain,tensioner, guides and labor. Well worth it I should think. Preventative replacement will,hopefully, save me some big bucks in the future. Good luck.

 

I have to agree with the general sentiment that a pre-emptive replacement is a pretty good insurance policy.

Speaking of non-interference (non-conflict) engines, one of the neatest ones has to be Ford's dinosaur 300CID I-6 truck motor, which features neither a chain, nor a belt, but instead the crank and the cam have gears that mesh together. That's also the way most aviation non-radial piston engines are.

 

Amen to that Ford engine. A friend had 300,000 miles on it when he sold the truck.

 

Smooth reliable truck engine. I had one for many years and all I ever (really!) did were oil changes. Company I worked for years ago had an in-house emergency lighting generator that used a city-gas powered Ford 300 I6.

 

I was looking at an 87 560SL the other day. I was really interested in this car until I noticed the spotty maintenance records. When I asked the woman if she ever had the timing chain work done, all I got was a blank stare. So, in addition to the car not starting (even with a jump), and the pool of red fluid on the garage floor, there were enough red flags for me to walk away.

The price was very low, but from what I've heard, a "cheap" Mercedes is the most expensive car you can own. So, the search goes on.

 

When a timing chain fails on an interference engine when, for example, at highway speed, what happens to the car?

In other words, is there a chance of the wheels locking up and the car skidding and perhaps hitting into other cars or whatever?

Would this be different for a manual or an automatic?

 

In other words, is there a chance of the wheels locking up and the car skidding and perhaps hitting into other cars or whatever?

Would this be different for a manual or an automatic?

Not much chance, and yes.

These cars are two tons of inertia. At highway speeds, there isn't anything in the engine (or anywhere else in the driveline) that could realistically do that. If you want to talk theory, then there's probably some way things could jam up with a manual transmission and cause the wheels to lock. In the real world if nothing else gives, the rubber flex discs would let go. And that's with a manual transmission, with a direct link from the engine all the way to the wheels. An automatic transmission, at least in the era these were made, has no direct link from engine to wheels, the torque converter is a hydraulic coupler that relies on fluid pressure. When the engine stops turning, the link is broken, and you'll coast to a stop the same as if you'd just shut off the key.