The small job of changing the O ring seals on the low pressure fuel pipes of a Mercedes diesel has turned into a big one. After changing the seals, I asked SWMBO to start the car while I worked the disconnected throttle lever on the injector pump. When the fuel got through, and the engine fired, it sounded more like something Fred Dibnah would be proud of than the nice smooth 6 cylinder rumble I was expecting to hear as reward for my work.
The engine is an OM606, so, it's a 24 valve, naturally aspirated indirect diesel. With the inlet manifold off, it was obvious that the noise was coming from the rear inlet valve, which wasn't sealing properly, and allowing exhaust gas to be noisily spat out of the inlet port. With the extensive inlet manifold in place, you can't hear the problem at all. The leakage must sound worse than it actually is, because the cylinder is still firing - albeit probably not contributing all it should to the cause of making progress.
Anyway, I'm now starting to get the cylinder head off, and I would like to ask how people tend to deal with the timing chains on these - I think that the main difference on these engines to earlier MB diesels is purely aft of the timing chain, as the cams are geared together, and counter-rotate, rather than both being driven directly by the chain.
I'm intending to mark the chain and sprockets for both the cam and injector pump, cable tie the chain to the sprockets, and rig up a system using welding rod to keep some tension on the chain at all times, to stop it coming off the pump and crack sprockets. I also intend to initially lift the head by an inch or so, and re-secure the chain to the front cover before relaxing my grip on the cam sprocket to all me to remove the head fully. Is my paranoia justified? Or am I just making a fuss, and in reality, there isn't enough clearance for the chain to fall anywhere untoward?
Number_Cruncher
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Sorry NC, other than to say that bungee type luggage straps are good for putting a tension on a chain in such circumstances I cannot help re this engine (must be a 91/92 to 95 E-Class I guess) though you are always forthcoming with support for others so here is a bit of moral support for you. Regards.
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not contributing all it should to the cause of making progress.
That's right up there with 'Non-Start Condition' :^D
Fantastic, N_C!
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"albeit not contributing all it should to the cause....."
That made me smile too!! :-D
Sorry - can't help with the issue of cam belt tensioning whilst working though (although I like the sound of using rubber bungees!)
Turtle
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Yep I use a bungee hung from the workshop roof. Then when the head is a few inches off the block carefully re-attach the bungee so that it is no longer going through the head... if that makes sense.
DW
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Completely unrelated to the Merc I'm afraid but that reminds me of the time I hung a Fiat 126 rear end from the roof when trying to get the seized engine out (it didn't like doing 70mph for 1/2 an hour one day). I tied a rope through the 2 rear windows and around the roof joist - better than car jacks.....
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For a brief while, I was beginning to worry that the backroom didn't have any experience to share - how wrong could I be?. Thanks for bumping the thread Cheddar.
Thanks to all for your input - I really like the idea of a bungee cord to hold the chain - it's probably a better idea than the bodged up welding rod construction I was considering. I've bribed a friend with some beer to help me lift the head off tomorrow evening, so I'll give the bungee cord idea a go.
The car is a '95 W124 E300D, and until this valve problem, I thought I just had a few quick and cheap tidying jobs to do! Oh well!
Number_Cruncher
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I wouldn't worry too much. There is a guide channel between the pump sprocket and the crank sprocket that will stop you totally loosing the chain! You'll be able to hook it out easy enough if you drop it down.
Don't know what you've done so far but you need to remove the tensioner unit (prime it with oil before refitting).
Ideally you should re-time the pump when you've finished the job.
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On the chain driven OHC engines I've rebuilt, my standard method of ensuring that the chain remains fully meshed with the crank sprocket is to use a couple of new, big car sponges. Approprately prodded into the chaincase, they will hold the chain in the correct position on the tensioner wheel and fuel pump/idler wheel and can easily be hooked out later... as long as you bought big ones.
As a general point, you must ensure that the chain tensioner can be reset in-situ. Mecedes and SAAB ones are OK, but on come engines, the tensioner will take up the slack and cannot be released without further dismantling.
If the cam wheel stays on the engine, use several cable ties to hold the chain onto the sprocket via the holes in the wheel web.
659.
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Thanks again for the help and advice - much appreciated.
I decided to take the vacuum pump off - it's driven by a face cam on the front of the injector pump sprocket. Once I did this, I saw the lower chain guide which Aprilia mentioned.
Instead of the sponges, I used some pieces of copper pipe, which I partially flattened, and used as wedges between the chain and housing - so, the chain is held on, and the sprocket is held in place too.
Having got the head off, I can now see that valve seat recession is not something that only affects the Isuzu engines in Vauxhalls. I suspect that its quite temperature dependent, bacause its only the rear cylinder that looks to be at all affected.
Number_Cruncher
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A bit of an update.
After having four new valve seats pressed into the head, I built it all back up last weekend. Priming the chain tensioner went well - an old jam jar full of engine oil, and a valve spring compressor were cobbled together to pump oil into the device. The engine is now running really sweetly, it starts really well, pulls well, and ticks over smoothly from cold - which was the original problem which made me want to fix the leaks in the low pressure fuel lines.
One great bonus of doing the head was that I changed the glow plugs, and could afford to be quite bold in my choice of torque to apply. There were two which were very difficult to get out, and these had carbon sooted up along their slender length. This makes me think that the real danger when fitting glow plugs is in not tightening them engough to get a good seal near the tip. The ones which had sealed correctly cracked off, and then unscrewed by hand, while those which had leaked fought every mm of their way out, and I suspect I was quite close to snapping them in the head - I was applying 50Nm to get them to move!
I also replaced some of the vacuum flexi pipes while the head was off, and this has improved the shifting of the auto gearbox - which is nice.
This vacuum system is something that's a bit new to me. I'm surprised to find that the fuel shut off is vacuum operated, and that vacuum is applied to the injector pump mounted actuator to switch the engine off! For this reason, there's also a valve, a little bit like a tap, on top of the fuel filter to shut the fuel off in case of a failure in the vacuum system. Weird!
Aprilia - is there a simple way to time the injector pump? The information I have suggests that this is done using electronic tools as opposed to spill timing as per the older models.
Anyway - thanks all, a good result! (I'm sure I'll be back with some more MB questions soon!)
Number_Cruncher
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mines a vacum turn off as well [ 5cyl] on mine theres always been a gap of 3 to5 seconds between actually turning key to off and the actual engine stopping, i can watch the "stop" switch o n pump slowly lifting while an assistant turns key , its not a problem but it makes passengers laugh that im nearly out of car before engine stops lol ,
re spill timing ive found this method quite easy , i connect a clear flexible pipe to the metal in jector pipe and run it down to crank marks, if you can put some diesel in pipe before hand by pouring some through this saves cranking and cranking.
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if you ever have the dash out like i have , theres three/ four ? vacum pipes going to ignition switch, the headlights are also vacum controlled to raise/lower , i found this out when after replacing dash the head lights were "on the floor" and found a pipe not clipped on properly [ my fault ] .
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