Yesterday I started my car at work (warm start), and noticed a soft birring noise that occurred when I hit the gas. I got on the highway and drove home, and noticed the car felt a little "off". Got a knock sensor code on the way home. Put the car in the driveway and restarted to move it forwards to the garage, and it started rattling. So I figured at least the tensioner had failed (car had the chain replaced by a PO a few thousand miles ago along with the head, and I doubt the tensioner was replaced (too many signs of lost parts not replaced etc to give me faith it was done by someone who cared)

Anyways, I checked spark plugs, which all look good, then removed the valve cover (pic below). The exhaust cam is off a couple of teeth, but look at the crankshaft. Just fyi, I was able to roll the engine over with a socket on the crank, so I don't think anything is hitting internally. Note that I couldn't feel any looseness in the chain before I rolled the engine over, which was unexpected.

I took off the tensioner, expecting the spring to be shot, since the slip seemed to happen on startup. And the plunger moves freely with a little drag, but appears fine otherwise.

Since the tension is off the chain now, I guess I could lock the intake cam, zip tie the chain to the exhaust cam, and rotate the crank to slip on the intake cam to get things lined up again, then install a new tensioner.

Just wondering if this sounds like a reasonable plan, or if there's something else I should be looking for.

BTW, no damage on the cams, no damage on the tensioner guide as far as I can see at this point.

Regardless, I won't know the extent of the damage, or if there is any, until I get everything retimed.

 

There's something wrong for sure either the chain stretched and it jumped a few teeth the harmonic balancer should be at O|T when checking the camshaft and sprockets for timing.

It appears your chain slipped somewhere and your timing is now off... Do you have missing teeth on any of your camshaft actuators/sprockets?

The top guide looks to be the original one if the PO just put a new head on it, it would of been easy to swap out all of the 3 guides up top.

Depending on how much work you wanna do i'd drain the coolant and remove the upper cover your going to need some RTV to reseal once your done.

There's also another chain below for the balancer (Lanchester) and a guide those maybe bad but I don't think it's a common problem like the timing chain and other guides but who knows.

I am currently in the process of removing the lower timing cover and it's a long process fortunately for me I caught the bad tensioner and bad sprockets before things could've gone bad I am going to look at the balancer guide and chains and replace it if there's any indication that it could go in the next 30k miles as I plan to keep the car for will over 250k currently at 189k.

Good luck maybe someone else with more experience will chime in.

 

It's weird since that top guide actually looks unmarked and the chain was tight before I removed the tensioner. I'm going to reinstall the tensioner and verify the crank pulley marks are true for TDC before doing anything else.

​​​​​​That it happened on start then got worse on second start makes me hope it was just the tensioner. Otherwise, as you noted, the project gets a whole lot bigger. Thanks!

 

First things first. Which code(s)?

Your sprockets look fine. If the chain is tight like you say, I think you're looking at the wrong thing. I don't think there is anything wrong with your chain or sprockets. As in you're wasting your money.

What's with the red marks on the sprockets?

I once had the timing chain inspected by a MB specialist indie. The mark you should be lining up for is not the big ones (where your red marks are), but the tiny little one towards the rear of the sprocket. See photo.


Exhaust cam mark

The intake sprocket may not appear lined up, but that's because of the variable timing system in the M271. In other words, if the intake sprocket doesn't have any obvious signs of damage, there isn't any useful information to be gained in this case.

With the exhaust cam lined up, the crankshaft pulley should be at 0 degrees ie TDC, but probably won't be unless the chain is brand new. According to the indie, any deviation below 7 degrees indicates an acceptable amount of stretch. In fact, my indie told me at the time that the job wasn't needed and that I should come back later with more mileage on the car. I'm still on the original chain several years later.

 

@slammer111 I think this could be a case of the tensioner being replaced and not the bracket.

If the PO replaced the chain and tensioner only with the newer version but failed to replace the bracket after re-reading the warning from Febi about only upgrading the tensioner but leaving the bracket as is?

Link to File provided by Slammer on Febi Chain Tensioner

 

This is my hopefully correct interpretation of the tensioner situation.

The original configuration (the way our cars left the factory) has 2 separate one way valves. There is one inside the tensioner bracket, and one inside the tensioner itself. The oil flows through the bracket valve, into the tensioner, through the tensioner valve, then comes out the hole at the end at the tensioner plunger tip.

A few years later, MB decided to remove the one that is internal to the tensioner. Newer tensioners have no valve. Therefore, with the new configuration, the oil now goes through the bracket valve, down through the tensioner, and out the tip.

With the original configuration, as long as either valve functioned properly, the tensioner would have the proper oil pressure. There is a redundancy in the system. Essentially there are 2 check valves in series.

With the new configuration, the bracket valve is the only thing maintaining pressure during operation. There is no redundancy. If the bracket valve fails for any reason, the tensioner system will no longer function properly, relying solely on the spring inside the tensioner. Guessing that the spring doesn't provide enough force.

The PDF addresses this saying that even if the tensioner was replaced, in some cases the chain may still skip from lack of oil pressure. This would happen if a) the new version tensioner is installed, and b) the bracket valve fails (from age for example). To eliminate this possibility, Febi recommends replacing the bracket, so that the bracket valve is new again.

I have a hard time imagining that the chain will have excessive slack as long as the tensioner hasn't reached the end of travel. If I were to guess, Febi just recommends a new bracket to avoid potential liability. The official MB timing chain replacement procedure doesn’t mention the bracket at all.

Here is a video on how a MB chain tensioner works. In fact, the guy in the video shows how the tensioner can be reset and reused.

**update** looks like this locking version doesn't apply to the M271. The M271 one doesn't have the clicky mechanism. It is only spring loaded.

 

Thanks for the responses! I'll get the bracket also. Only code I got was the knock sensor, but that was before I started it again in the driveway and it started rattling. I used to be active on a n English cars forum and they always talked about DPO's, or Dreaded Previous Owners

 

One question, while I wait for parts to come in:. Most every video I saw has the ratcheting tensioner. However, this one seems to be just a spring loaded plunger with a hole for oil. I wonder if they changed designs based on lousy performance.

 

It's the same spring loaded tensioner well at least that's the that came with my kit.

The video shows a totally different tensioner than what we have.
Here's the old tensioner being broken with collar coming out and the new one.

 

Interesting. Yeah I was sort of wondering about that. With that said, a clicky locking one would've made way more sense than a spring loaded one in general.

^ Any chance you can open up the old one and see where the one way valve is located? I suspect it's inside the plunger piece that moves.

 

This looks like it maybe it....

 

Yes that looks like the valve. Where in the tensioner is that located? (Haven’t had a chance to physically look at one on this end)

 

That's a photo of the inside i removed the plunger and spring this is looking into where the bolt is located if that makes sense. It's the part that is actually screwed into the bracket.

 

Based on what you're seeing now, is there any reason why the tensioner cannot be reused? Does anything actually wear out internally, other than possibly the 1 way valve?

Yes I understand the plug is one time use, but a new plug is much cheaper than a new tensioner.

Also can you check if the new tensioner you have contains the 1 way valve? I'm wondering if the Febi kit still contains the old style tensioner. Guessing MB removed the valve in the new tensioners out of cheapness. If this is the case, then the old style tensioner is the way to go.

 

The new tensioner doesn't come apart like the old one lol

Sorry to OP for Hijacking your thread...

The old tensioner if you see in the photo in Post # 9 has that cylinder coming it out its sticking out (silver color) and does not want to go back and I didn't want to waste my time figuring out how to push it in. Theres appears to be another valve on the opposite side on the end that pushing against the chain guide or some mechanism when I push down on it oil squirts out of the hole.

FCP euro has the tensioner/adjuster for $86 with lifetime warranty or the Febi for $80 i'm assuming they are identical and Febi makes this product for MB. Or you can buy the short kit for $126 comes with guide, chain and tensioner...

 

I think Febi is more of a repackager of OEM parts in many cases. For example, Jwis makes the timing chains for MB. Febi is not in the chain manufacturing business. I'm pretty sure a Febi thermostat for the M271 would still be made by Wahler, who also make them for MB.

 

OP here. I got the upper timing cover off, and FWIW aligned the cams by sliding some aluminum thin sheet between chain and sprocket. They weren't that far off. Now both of them are at TDC and locked in with a tool. I say "FWIW", because a) the crank is still 45 degrees before TDC, and b), I still need to get to the tensioner holder/bracket/whatever you call it, and it's obviously under the lower timing chain cover. Lovely.
Looking around, I'm finding nothing regarding a how-to for getting the lower timing chain cover off for the m271 engine. Just looking at it, I'd say "everything you can see on the front of the engine; take it off". That means disconnect power steering pump, take off the water pump pulley and water pump, remove air box and supercharger, disconnect the air conditioner compressor, remove the crank pulley. Then it looks like I need to lower a cross member and the pan. Am I seeing this right?

If someone still has access to the WIS and has the instructions, that would be helpful. I've worked on a lot of cars in my life, and unlike most people, I have no problems with a timing belt; just replace them as needed. They're comparitively easy to replace. When they shifted designs from belts to chains, it seems a lot of manufacturers did almost zero testing, just blindly thinking "this will last the life of the car'. So they buried the chain under so much else that it's a huge effort to fix. The later m271's have a much more robust looking chain.

Someone asked about the red marks I had on my sprockets. Mine lined up with the small marks on the cam side, so it was a nice visual to keep.

 

You are correct all accessories need to be removed power steering steering, water pump, idler pulley, you need the tool to hold the harmonic balancer to remove it. You are going to want to buy new seals and o-rings for the water pump and crankshaft seal in addition to have some black RTV or some of the MB seal. Here's my thread on it New Chain and Sprocket I just removed the timing cover I didn't have to drop the pan but I might have to when I put it back so it seals properly i'll update the thread later I am tired.

 

Thanks! I'll start following your thread. Unlike you I have a failure on a system with new chain, healthy guides, and apparently ok tensioner. So I have to think the tensioner mount valve is stuck. With all the rtv used in place of gaskets on this engine, something getting stuck in a tiny valve wouldn't surprise me. I did get my crank and cams aligned by slipping the cams back so I could roll all forward to TDC at the same time.

 

I would also look at the crankcase pulley (harmonic balancer) to see if there's any damage. The elastomer part (the part that connects the inner and outer sections) can go bad which can cause the outside pulley to rotate/slide against the inside. Not too common but it can happen.

For some reason I still think you're focusing your effort on the wrong part of the engine.

 

Slammer, I saw some posts on the big pulley and did check to make markings were true. I'm all for suggestions for where to look; I don't like being in a situation of not having an obvious cause, and replacing the tensioner and bracket is about all I know to do. I can look at the crank sprocket while I'm in there.

 

You mentioned your car threw a code. Which one was it?

For mechanical parts, my rule is always to confirm something is broken visually before throwing parts at a problem. Saves a pile of money. I am not convinced your chain or sprockets are the problem. The chain looks tight and the sprockets don't look worn at all. I assume you would've mentioned it if you found any slack in the chain.

Have you checked your ignition coils? Sometimes they partially fail before completely dying. My car was occasionally stumbling (it would miss a beat once or twice a day) in the weeks and months leading to a coil failure. When they do die though, they throw a CEL.

 

I now have everything coffee the front and side of the engine. I had forgotten how frustrating getting the supercharger out was. If I hadn’t bought ratcheting etorx wrenches for all the tight spots you can’t get a socket to fit I’d have lost my mind.
The only reason I’m doing this is because the tensioner bracket failing is the only thing explaining why the chain slipped as it did. And to get to that requires the same work as the guides and oil pan.
I have to think that it might require less time to pull the engine and trans than going through all this. Too late now. Next up; pulling the crank pulley, lifting the engine, removing the pan, etc.

 

Off, not coffee. Seriously autocorrect?

 

^ You know you can edit the post instead of posting again right?

And yes removing the supercharger is a pita, especially for the screw closest to the tensioner.