380 timing Chain
 

Tow truck just delivered the SL. Wouldn't start while wife was running errands. Looking under the hood I find the left cam cover cracked over the chain. Pulling the cover, I find the a piece of the upper guide stuck between the chain and the cam gear. A few more pieces visible in the chain run. I will get into the Maint CD this weekend. Looking for the best course of action. Hoping I can confirm the timing marks are still aligned. If yes then I am assuming I don't have valve/piston interference and can just repair the chain/guides. Correct? Or do I need to do a compression check before I get it all apart?

Assuming I will have to pull all the front covers to collect all the broken bits. Yes/no?

When I bought the car the PO gave me a receipt showing the chain/guides were replaced about 80K ago. From what I can see, the guides are dark brown and look pretty brittle. Think the PO got ripped off. Was hoping to get several more years before I worried about the timing chain at around the 100K mark.

Any tricks I need to know that aren't in the Maint CD?

Ouch... Hopefully your engine was not destroyed.

That is what worries me about my 85' 380SE. It has 264K and I have NO IDEA when the timing chain/rails or guides were last changed - if ever. I talked to a MB specialist and according to him, if I did not hear my chains rattle when I started it up, then they were likely OK. It does not make any noise up there, but it is not knowing when the guides/rails were changed is what concerns me. The way he was talking is that even if they break, that engine damage is still not certain.

I am hoping that with this high mileage on my car, that they have been changed before, or they would have surely went by now? It is a 21 year old car and I am really not wanting to sink a lot of money into it. I was quoted $525 for the chain replacement and was told it would be "significantly more" to change the rails/guides, as it required even more tearing down of the engine.

No more than I paid for it, I will just drive it until it hits the road, without sinking in a lot of money into it, or else it will all be money out the windows. :rolleyes:

Good luck to you!

BTW- what year is your SL? Does it have the double chains, or the single?

it seems to me
 

that if your timing chain is not broken, then it is unlikely that any valves hit pistons. but a compression test is pretty easy to do. so yes, i would do that. i dont know about the other quesitons but i seem to remember hearing that the front covers must come off.

tom w

Taking the cover off is a big job compared to changing the chain and other things, but I don't think that there's really a choice, assuming that you got "lucky". I wonder if some pieces wound up in the oil pan.

Keep in mind that as far as I know, any 117 engine valve covers will fit. On eBay, 380/560SL valve covers are very expensive. SEL valve covers are cheap! But ask if they are cracked - I got a set (to polish) with - guess what - the left valve cover cracked - seller "didn't notice".

If I were not willing to sink a lot of time and/or money in a car, I'd replace the tensioner (only). It's only about $70-$80, and replacing it really only involves taking off the alternator (maybe), the water bottle (very easy), the valve cover (so you can see what you're doing), and the tensioner itself. Mechanical skill requirements are not very high, but like anything in this area, no mistakes are permissible. I prefilled mine with oil before installing - old MB manuals say to do this, newer ones don't. I couldn't help but notice my tensioner in a box marked THIS SIDE UP (shipped upside down, of course) in a bag full of oil, and the tensioner "piston" loose...

I think that a lot of these catastrophic problems START with the tensioner allowing the chain to slap, because the one-way valve gets old, and it drains back oil and loses tension quickly when the engine is stopped. That's why when this happens, it often happens when a car is started. I'd say that chain stretch would have to get really, really extreme before reaching the limits of what a good tensioner can compensate for.

More info
 

My SL is an '85 with 188K miles on it. I double checked the invoice and it sayed the tensioner was also changed with the chain. It does have the double row chain.

It did occur when trying to start the car. Wife said it did make a funny noise when it happened. Guess I was fortunate that it didn't start. I was concerned about piston/valve interference because of it not starting. I'm now thinking that the friction of the chain on the valve cover wasn't letting it spin fast enough to start. The inside of the cover is very gouged.

the valve cover
 

is probably repairable. i once had a side cover repaired on my 350 harley/ benelli by a local hot rodder with a heliarc. after welding the parts back together he hit it with a grinder and buffer and it was impossible to see the repair from the outside.

tom w

188K. Hmmm. I am thinking that mine has surely been changed since it has 264K on it. It only has had two owners, you would think the original owner would have kept some records. :rolleyes:

I may go with that idea of changing the tensioner only, but may not. :)

I hate to be the messenger, but you have bent valves on the left bank. You can do a compression check starting with the left bank, but you can also pull the left bank valve cover and check for loose rockers. At that mileage I would recommend a complete valve job rather than just doing one side. In 30 years I have never seen an MB V8 with a piece of the inner left bank rail stuck in the chain that didn't have bent valves.:(

Thanks
 

That is just the type of info I was looking for. This is my first time into a MB V8. Is it possible to see a bent valve without removing it? You said look for a loose rocker. Shouldn't all rockers not on a cam lobe be loose?

Curious how the valve would get bent. It does not look like the piece stuck in the gear is large enough to cause the chain to skip a tooth. It happened before the engine started so the RPMs were very low. Even if there was a momentary stoppage of the cam one would think there would be enough clearance. I am a firm believer that experience speaks, I am not doubting it. The backyard engineer/tinkerer in me is just wants to understand it.

Rockers operated by hydraulic lifters are always under slight pressure unlike mechanical lifters that are set with a clearance. That piece of plastic stopped the chain from turning the cam but didn't stop the pistons from going up and down. I'm not saying all the valves are bent. Only the ones that were open when the cam stopped turning are bent.

Before you spend too much money you might go to the local parts supply and pick up a can of valve straightener and pour it in the oil. There are several brands. One is as good as another. I don't think the dealer carries it' They always want to sell you a valve job.:D

valve straightener
 

a joke, right?

tom w

If it were my car and the same thing happened to me, I'd try to pick up a used engine of the same caliber and replace it. It's got to be cheaper and less headache than diagnosing and repairing the "rattler".

Oh, you could buy my entire car for $2k. I just did the timing chain, tensioner and guides. It's a 380SE with 120k miles on the clock. :)