1 second engine rattle on cold start up (M271)

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Off work again now and will keep this job moving. Undertray to come off, power steering pump and alternator to be moved. I have some new coolant so I’ll drain the old. I’ll order the cam solenoids tonight as well.
 
Decided to order a chain crimper to get this job done sooner rather than later. Everything has arrived other than my new thermostat, and cam magnets, which should be here in the next few days. I think I will leave the current guides in place, as I have inspected them and there seems to be no visible wear. All being well I should get this work done over the next two days.
 
Update: New chain has been fed in from the top and now the old chain is delinked and out.

Have a small problem, in that I opted not to get the camshaft locking tool. When I delinked the original chain the sprockets moved slightly, as if they were under tension. I can lever them back in line with the timing marks using a big screwdriver, but they do not stay there, and move back to what appears to be a resting point, half a centimetre away from the timing marks.
 
Update: New chain has been fed in from the top and now the old chain is delinked and out.

Have a small problem, in that I opted not to get the camshaft locking tool. When I delinked the original chain the sprockets moved slightly, as if they were under tension. I can lever them back in line with the timing marks using a big screwdriver, but they do not stay there, and move back to what appears to be a resting point, half a centimetre away from the timing marks.

Surely something can be improvised to lock the sprockets in place.....?
 
Further update: the exhaust side camshaft adjuster is solid when I try to move it with my hand, but the adjuster/gear on the intake side has a few millimetres of lateral play in it, just wondering if this is the norm or if both sides should not move at all.

I believe these gears have a locking pin that is supposed to prevent this and they are prone to wearing.

It was on the intake side that the chain was making contact with the top of the engine cover.
 
I have completed the job successfully 🙂 will post a short piece soon with some notes for anyone attempting this job in the future. Rattle on cold start has gone and it runs well. Very pleased .
I’ll look forward to reading that . Good work buddy .
 
Well done!
 
Hi all,

Apologies for the delayed response on this thread. Due to the help and input everyone gave I have had it in my mind to reply here with my experiences for anyone attempting this job in the future.

Firstly, I did successfully replace the timing chain, camshaft magnets with pigtail extensions (cheap eBay ones, they work fine) and the chain tensioner. However, after a short while I noticed the engine is the same if not a little noisier on startup, so the issue was not resolved!

I am now thinking the issue is with the bottom chain that runs the oil pump, or the pump itself, leading to a slow building up of oil pressure and the tensioner not working as effectively for the first minute or two of the engine running. Just a hunch I have. This job is outside of my ability to complete at the moment. The car is currently parked up SORN as I have a company car, so perhaps one day I’ll get the engine out and do this job, but otherwise the car runs lovely and has had many long trips.

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For those attempting the timing chain replacement, here are my tips (not a guide, just tips to accompany whichever proper guide you are following):

Try to remove the camshaft/rocker cover without removing the air box. Removing the air box adds a lot of extra work and tedium, and you will need flexible long reach hose clamp pliers, without which you will eventually find yourself driving to a shop to get some. I have seen people post saying they removed the cover without touching the air box.

There are some retaining screws at the back right of the engine bay that keep the wiring loom tight to the top of the cover, try to remove this to give yourself enough play in the loom to shuffle the rocker cover out from underneath it.

Once you have inspected the chain and gears, and have decided the chain is to be renewed, I would avoid all the cheap chain splitting and crimping tools around. I tried these and found the crimping tool did not have a sufficient recessed area to crimp the chain without fouling on the next link.

Camshaft locks are a necessity in my experience. I broke the chain without them, and the cams immediately fell to their rest position. I tried to lever them back in line with the timing marks with a screwdriver to no effect. I eventually bought some camshaft locks and was relieved to have everything aligned and secured. You could definitely fashion this out of wood if you have time and are handy with tools, or have low funds, but if not, get a set of camshaft locking tools.

I’d suggest stuffing the front of the engine with rags and breaking the chain with whatever tool does the job.

Needless to say the chain does need securing once broken. It can rest quite happily on the sprockets until you are ready to progress further.

Regarding the crimping of the new chain, use links from the old chain to attach to the new, and put half a crimp on them to keep the chain in place. If you had thin (but strong) enough wire, or very small and thin cable ties, I don’t see why this wouldn’t work, but make sure you do not create anything that will not allow the chain to run along the sprocket. Anything protruding too much, like a thick cable tie, would give rise to the possibility of the chain not seating when you feed it around. I only had thick cable ties and decided against it. Tiny ones would likely be fine.

You can feed the chain around by yourself, but be warned, if you do not keep it under tension it will run into the bottom of the engine. I stopped this from happening twice. Hair raising stuff. You can hold the side of the old chain with you left hand, put your right elbow on the new chain side to keep tension, and use your right hand to ratchet the crankshaft. If you have an assistant that’s a bonus, or if you are not the confident type, just wait until someone can spare 10 minutes to help you.

Once the new chain is fed in you will need to crimp it up.

A poster had suggested using the Sealey motorcycle crimping tool for crimping the new chain crimps. I almost went down this route, but then decided the cheaper eBay tool would suit me better, but the tool turned out to be poor, and fouled on the links next to the new one. If I could do this job again (which I may one day depending on what is involved with the bottom chain), then I would absolutely use the Sealey motorcycle chain crimper.

All you have to do is look very closely at existing crimps from the factory, and aim to replicate these with the Sealey tool. It is much easier than I expected. There is a lot of faffing about with the Mercedes crimper tool that would be avoided with the Sealey.

Your new chain should be the correct length to ensure the right tension. Just ensure you pull the chain tight to the sprockets, but do not force it to the next tooth on the sprocket, and crimp wherever the new link sits. Once the tensioner is back in and the engine is turned a few times, it should be tight and like new, just as mine was.

The cheap eBay tool gave me poor crimps, but I also overtightened it, so a warning to those with this tool, just do it lightly then check it, and apply more pressure until you are happy with the crimps.

Finally, ensure everything is re-fitted correctly before testing driving, or like me you will get a warning light and a panic that your timing was out, when the supercharger cooler pipe was not in place properly. Relief. :)


Thanks all for your help.

Hope this helps anyone attempting this job in the future. It is more than doable by someone with some light experience of using tools, and a bit of confidence.
 
Just started it up to let the engine run up to temperature. No rattle. I think it’s a cold start related issue. Something to ponder.
 
You have a C200k then.
As an aside, what sort of economy do you get on a run of 10-20 miles?
I feel sure mine is not doing that well at around 33mpg.
I dream of getting 33 mph out of my CLK 500
 

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