Timing Chain Failure

[Naj ✝︎]

Anybody here ever experience timing chain failure?
I think I just may have  

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naj

65 230SL
68 280SL

[ja17]

Hello Naj,
Ouch, that is a depressing sight! How many miles on that chain. Failure almost never happens before 100,000 miles or more.

Joe Alexander
Blacklick, Ohio

[Cees Klumper]

That's it. I am replacing my chain ASAP ... Very sorry that happened to you. Only a few years back you warped the head due to overheating?

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[A Dalton]

Originally posted by naj

Anybody here ever experience timing chain failure?
I think I...


 What makes you think it is chain failure???

[A Dalton]

quote:Originally posted by ja17

Hello Naj,
Ouch, that is a depressing sight! How many miles on that chain. Failure almost never happens before 100,000 miles or more.

Joe Alexander
Blacklick, Ohio

 ..unless one has a leaking/bad tensioner....

[Khurram Darugar]

Damn that really sucks! Im really sorry to hear that.
Kay

[Naj ✝︎]

quote:What makes you think it is chain failure???

I was approaching a road junction. Probably dipped the clutch already. There was a sound like something broke. Engine stalled. On cranking, it turned just a bit. On second attempt it was completely locked up. Had it towed to a friend's garage. He could not see the chain from the oil filler. Too late to take valve cover off. Will investigate Monday.

 

quote:..unless one has a leaking/bad tensioner....

Tensioner tightened the chain quite well on reinstall of 250 head.
Chain slackness not audible when engine was running hot in a traffic jam a few weeks ago. Engine temp went up above 180 mark (mormally below) and oil pressure fell to just above 30 psi at idle, (normally pegged at 45psi)

 

quote:Ouch, that is a depressing sight! How many miles on that chain. Failure almost never happens before 100,000 miles or more

Total mileage is 96K. Engine rebuilt by PO and has O/S 020 pistons.
I changed head from 230 to 250 when head gasket blew because head had not been retorqued by PO. Chain looked good and there was a wide gap between the lever on the chain tensioner wheel and oil well on head. Have done <2k miles since head change.


Is it a 'stuck open' exhaust valve that would hit the block/piston top when attempting to turn the crank?

naj


65 230SL
68 280SL

[ja17]

Hello Naj,
If a  chain lets go it will usually fall into the engine and  jamb at the crankshaft sprocket. The sprocket is usually damaged along with some chain rails and the chain of course.

A piston can come in contact with the valves as the valve timing get out of sync. Since the valves are verticle in the head they usually will not bend however the camshaft  or the cam holders can be broken as the piston drives the valves upward.

Since your engine was at low speed your camshaft and valves may be ok.

I would be suspicious that your masterlink on your timing chain may have somehow become uncliped or may not have  been clipped properly during your last head work. These chains and tensioners are exremely durable. Always use original equipment timing chains. I have seen very poor quality aftermarket timing chains which can fail!  

Another possibility is that something like the timing gears jambed causing the chain to snap. Not likely since you recently checked and shimmed these as I recall.

If you have not suffered valve or camshaft damage you can fish a new chain in after replacing the damaged sprockets and chain rails. I can provide details. Let us know what you find.

Joe Alexander
Blacklick, Ohio

[Naj ✝︎]

Thanks, Joe,
Lets see what tomorrow brings.

naj

65 230SL
68 280SL

[Bearcat]

told my mech abut naj's disaster....he has been stripping/rebuilding these engines for the last 30years. He tells me its very bad luck....they rarely let go but when they do it can be pricey...besta luck naj but i think you'll be raiding the savings jar.

[Naj ✝︎]

Joe,

quote:If a chain lets go it will usually fall into the engine and jamb at the crankshaft sprocket. The sprocket is usually damaged along with some chain rails and the chain of course.

Yes, its the chain and its fallen into the cavity.

Can the sprocket on the crank be removed from the oil seal hole or will the engine have to come out? Also, the rails, can they be replaced in-situ? 'ASS'uming there is no valve damage.

naj

65 230SL
68 280SL

[ja17]

Hello Naj,
Yes the sprocket can be removed with the engine installed.
Remove the hood. Remove the camshaft sprocket.  Remove the chain tensioner sprocket and arm so you can get a good view of the inside of the chain gallery (watch the spring does not fall into the engine). Drain the oil and remove the steel oil pan (sub pan).  Remove the oil pump and the front main bearing cap.
At this point you can assess the situation. You should be able to remove the chain and examine the crankshaft sprocket. Examine it closely, if it is worn or damaged at all it must be chainged or the disaster will happen again.

Remove the rocker arms and spark plugs and inject a little air through each spark plug hole. With the rocker arms are off, each cylinder should hold a little pressure. If you get a major leak a valve may be damaged.

If the valves seem ok, remove the radiator, vibration dampner, pull the front counterweight and front seal. Drive the crankshaft sprocket out of the block from below. You will have enough room with the front bearing cap off!

Your injection pump and distributor will be out of time so removal is needed also at some point. Check the to make sure the cahin sprocket driving the injection pump turns, this will tell you that the timing gears are probably ok.

I will go over re-threading a new chain this evening. Good luck and hang in there!

Joe Alexander
Blacklick, Ohio

[Mike Hughes]

quote:Originally posted by naj

Tensioner tightened the chain quite well on reinstall of 250 head.
Chain slackness not audible when engine was running hot in a traffic jam a few weeks ago. Engine temp went up above 180 mark (mormally below) and oil pressure fell to just above 30 psi at idle, (normally pegged at 45psi)

What sort of noise would a slack timing chain make?

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[J. Huber]

From a very un-mechanical type: Is this timing chain and tensioner something that would be replaced if #1 -- the "top end" of an engine was rebuilt? And #2: how about if a new "Short Block" was installed. Thanks. Good luck Naj.

James
63 230SL

[Benz Dr.]

Most likely to be the intake valve that hits first. The exhaust sits much farther up in the head. Very uncommon for chains to break - it's usually something else that makes them break.

Had one once where the lady said her car was making noise. '' Show me, '' I said.
So she starts it up, or trys to before I stopped her. It was making this god awful noise like a jack hammer.

 Once I took it appart it showed a snapped conecting rod with the broken piece flying around hitting the block and bottom of the piston. There was about 1/2 liter of oil in the pan so I think it was run dry. Chain looked good though.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org

[ja17]

Hello Mike,
The chain tensioners will usually last the life of the engine. They are very reliable and durable. It tensions  hydraulically from engine oil which puddles up in a small oil pool built in the chain gallery of the cylinder head. This "oil pool" is situated under the tensioner arm and one of the 6mm allen cap bolts is located in this "pool".
The tensioner also has a spring but the real work is hydraulic. Movements from the tensioner and chain "pump up" the tensioner. As the chain stretches it reaches the point where it will not "pump up" any further.

If the tensioner or the chain is extremely loose you will get a low pitch rattling noise. You may also see rub marks where the chain flops against things in the chain gallery.

It is difficult for a good chain to break or jump even if the tensioner is bad. But if you have a very worn chain, badly worn or damaged chain sprockets, or some other mechanical failure, it can jump or break even with the tensioner working properly. If the washer or bolt  you lost during engine work happens to fall into the crankshaft chain sprocket your chain may jump or the sprocket can be damaged. I always replace the crankshaft sprocket during a rebuild. This sprocket takes a lot of work. Sometimes the key of the crankshaft or its groove wears!

If the master link clip falls or is knocked off or is improperly installed, the chain may separate.

Sudden chain failure is very unusual, I suspect NAJ may find another issue which caused the separation of the chain.

The 100,000 mile rule is good insurance if you are not certain about the history of your timing chain! Change it during major engine work like a valve job or engine rebuild if it has never been changed.

Joe Alexander
Blacklick, Ohio

[Ricardo]

I know this probably doesn't relate exactly, but I have all the service records for my '83 300td wagon from 47,000 miles on.
It still has the original chain, sprockets, tensioner etc. and just turned 250,000 miles (418,000 kms.) last week.
Did I just jinx myself[:0]
Ricardo

[ja17]

Hello Recardo,
Diesel timing chains have a heavier duty timing chain. However they have to handle a lot more strain from very high diesel compression. Naturally if most of the miles on the engine are  long trips and highway miles, much less demand is placed on the engine.

However at a qurter million miles I would definately have the chain checked first chance! I just replaced a broken timing chain on a diesel with about the same miles.

Joe Alexander
Blacklick, Ohio

[German Dude]

Naj,
not much in the way of consolation, but I just took a look at the pic. And may I say this has to be one of the top three color codes for a pagoda.

I think it is extremely helpful when a car looks like this - you know what you are spending your money on.

Good luck

Juergen

Juergen
64 230SL #2933, 4sp, signal red, white hard top
93 Citroen XM station wagon

[ja17]

Hello Naj,
I can't stand the suspense! Any progress yet?

Joe Alexander
Blacklick, Ohio

[Malc]

Naj,
Sorry to hear about your failure. It's sickening I know I had a cam belt let go on a VW diesel engine when the water pump failed.

I'm of cause not sure what cause your failure, but it maybe that your oil pump is worn out or has been damaged, loosing oil pressure would effect the tensioner which in turn may of caused you chain to jump.
Suggest the following, sorry to repeat other's who have said anything before.

1) Remove cylinder head to check for bent valves or damaged pistions.
2) Remove the sump and if possible can you get the oil pump out without removing the engine (somebody will know).
3) check pump is within specs
4) replace all chain components if bits are smashed try and save all the bits you find so you can check that you don't end up with bits of metal floating around your engine.

If there is any evidence of a valve hitting a piston I would strongly recommend that you remove the said valve and roll test it to see if it is bent.
Next once all the chain bits are removed use a dial gauge and check that all the pistons come up to TDC in each bore at the same position. if one was involved in a collision with valves and it does not you could have a bent con rod.

When my VW engine did this I found some "scarring" on the top of some of the pistons but the pistons/block heights came out all right. A little careful work with a file removed the worse of the burrs etc.
I had to replace all the valves, hydraulic tappets and of course the water pump and put the sump back on!
12000 miles later it's still going ok

Hopefully you can do these checks/work without having to remove the engine
Hope this helps and encourages
Good luck
Malc

[Naj ✝︎]

Hello Guys,
The suspense is killing me too.
Instead of taking the hood or valve cover off, the mech went out and bought a car cover, moved the car in a safe spot and covered it up!!
He was too busy last week.
Now, this is a short week because of the holiday on Monday. So, fingers crossed.....
Do appreciate all y'alls kind thoughts and comments which I will certainly take on board.
Thanks
naj

p.s:
 

quote:but it maybe that your oil pump is worn out or has been damaged, loosing oil pressure would effect the tensioner which in turn may of caused you chain to jump.

Oil pressure is normally pegged at 45psi. Only after sitting in traffic for an hour and a half one satruday afternoon, the temp gage headed north to just above the 180 mark, and the oil pressure gage south to just over the 30psi mark. Quite acceptable?
(The pagoda article in the ME quoted 15psi as acceptable when hot  :evil: )

naj

[A Dalton]

<<the temp gage headed north to just above the 180 mark, and the oil pressure gage south to just over the 30psi mark. Quite acceptable?
>>

Quite.

[ja17]

Hello Naj and Malc,

Good advice Malc on finding all the broken parts! I ounce did a top end rebuild on a Datsun engine. It had dropped a valve. I was un aware that a piece of debris had blown into the intake manifold as the engine broke. I rebuilt the top end, fired the engine up........the debris was sucked back into the engine,!!!! I did the job again!

Now the oil pump should not effect the chain tensioner. There is no pressure oil feed to the tensioner. The tensioner is a little hydraulic pump which generates its own pressure by chain movements of its arm. The oil is simply scavenged from a small pool built into the cylinder head chain gallery.

An eventual compression check should give you the status of the valves, pistons etc. Since the valves are verticle in the head they may survive an impact. However check the camstands closely they may not survive the jolt.

Joe Alexander
Blacklick, Ohio

[Malc]

Joe,
As you can tell I have yet to really dive into the old dears engine. How does the chain tensioner "pump" it's self up?? Are there seals in it that can wear out? If it got too hot ie the oil, would that have any bearing on the pressure it applies to the chain??
If not seals does it just rely on a "good" interference fit to stop it loosing both oil and pressure?
Just one more thing to check when I pull it to bits!
Thanks
Malc