Well I had read a great deal over the years about major engine problems with the M271 four cylinder petrol engine that had taken over from the slightly older M111 unit. For me it had been just something you read about, until last week when the wife’s C200K (2004) slipped a number of teeth on the cam gear and destroyed itself while attempting a start in the drive at home.
This car had covered 80k miles always been regularly serviced at the correct intervals and to be honest is a cosseted example of the marque! Even so it fails to escape failure of the M271’s achilles heel – the timing gear.
Taking the call from work I new instantly what the issue was and it was only confirmed when arriving home. I coupled up the code reader and sure enough after a read, there were several cam synchronisation errors, only possible if things were not dancing in tune.
Removing the valve cover revealed what I knew was true, moving the flywheel to TDC showed the Inlet cam to be over 30 degrees advanced and the exhaust to be 20 degrees retarded, wow thats done damage!
A quick compression test showed zero compression on any cylinder so we had to put this right.
In many cases where this happens and perhaps the car is not the most shining example of the model, the repair cost is many times that of the value of the vehicle and the owner decides to scrap the vehicle or sell it on ‘spares or repair’. In this case, where the vehicle is a trusted family car in very nice condition, just MOT’d with a good body and leather, I could not imagine sending it to big scrap heap in the sky – it was going to be fixed!
Tearing down the engine and placing all the parts in the boot as I went was the first call to action, not only did I want to see the extent of the valve damage but also the degree to which the pistons may have been damaged.
Once the cam gear was removed and manifolds disconnected, the head could be lifted to reveal what lay beneath. Thankfully this operation revealed a set of undamaged pistons, with just the slightest indentations where they had met the inlet valves, nothing to worry about there as the exhaust valve-train looked totally undamaged. So good to go!
I spent a couple of days researching new parts prices and with a mix of Ebay and Euro Car parts sources all I required for the rebuild for a fantastic £220 inc vat! The two VANOS (variable timing) cam gears were suprisingly not showing any more signs of wear that would be expected for the mileage and close inspection showed little wear either to the profile or contact points where the drive is transmitted to the dog from the chain. If these cogs were damaged or worn the replacement cost for these components alone would be £500. (www.M271.com is among a few others the UK source for these two gear components should you need them).
The list of parts I purchased was as follows:
Febi Cam Chain and Tensioner Kit inc Guides and Tensioner Bung
Timing Chain – Extra link
8x Inlet Valves for Intervalve (Euro Car parts)
16 Valve stem seals
Valve Grinding Paste and Stick
Reinz silicone gasket sealer
Elring Head Gasket
Cylinder Head Bolt Set
Vaico 3 Pipe Breather pipe set and non-return valve (located under supercharger – more on this later!)
2 litres of Antifreeze
2x Rubber bungs for timing chain guide pins/cylinder head
1x 2.5 diameter inch Jubilee Clip to replace the ‘spring type’ one mounted on the rear of the air box/MAF pipe
1x Big bag of ‘Good Luck’
Once all the parts had arrived I removed the old valves from the cylinder head and ground in the new replacements, fitting the new valve stem seals as I went. After a tedious time cleaning off the sealant debris from all mating gasket surfaces it was finished ready to fit.
The block was now going to have the post mortem, as I felt only the chain had stretched and caused this issue because it was no longer able to held in good tension by the hydraulic plunger-type tensioner. Removing the alternator revealed a large bung that gave access to the cam chain tensioner inside the timing cover, once removed the tensioner within simply unscrews out with a 17mm socket (40Nm when it goes back in). In combination with the removal of the right hand chain guide, enough timing chain can be hauled out of the timing cover to safely split a link and attach the new chain to the end of the old one and wind it through. I measured the new chain on a hanging flat surface and comparatively measured it against the old one when it was removed. The old chain had stretched about 12mm – which equates to adding an extra link to the timing chain. This would have resulted in a mechanical 20 degree retarded valve set over TDC. Once elongated to this extent the snatch of the chain in each cycle works the links of the simplex chain doubly hard and the wear simply accelerates.
As a quick check on an engine that has not yet failed, is if you lift the valve cover and set the crank to TDC, you should see the timing marks on the cams-to-carrier align perfectly for a good timing chain, a worn cam chain or gears will exhibit a misalignment in these marks, namely rotating the crank beyond TDC to align the retarded inlet cam, that when aligned with its index will further show a trailing exhaust cam by about one tooth! REPLACE IT QUICK!
The tensioner on my engine had almost extended to the end of the piston, at this point because of the level of extension, hardly any spring pressure was being transferred to the tensioner guide – meaning in a start-up scenario, where low oil pressure would be ‘building’ in the tensioner it would rely pretty much on only the spring to cover the interim time until oil pressure begins to holds things in place. This without doubt is why the majority of failures happen on starting the engine and very rarely when running to road speed.
Mercedes in their wisdom, tried to patch the issue by adding a small non-return valve to a modified tensioner saddle mount, the idea of this was to control oil seeping back from the tensioner during periods of standing, assisting the pressure ‘build up’ speed from a start. It didn’t seem to help the widespread failure issue, just made the engine quieter until it had turned over a few times on start up. It I think was really more a case of the chain wearing beyond the limits of adjustment at the tensioner mechanism, whereby after which its only a matter of time until disaster strikes.
Once the timing chain has been fitted and head replaced the timing can be set perfectly to align with all three marks, confirming all is well. Screwing in the tensioner fully, having secured the guides with their pins, the engine can be turned with a socket on the crank nut to prove your work.
A screwdriver confirms absolute TDC inserted through the plug hole of the frontmost No.1 cylinder. It has been known for the harmonic balancer rubber to delaminate on the crank pulley – shifting/pulling the market TCD position round to an arbitrary point on the circumference as the faulty pieces slip round each other. Obviously this needs to be replaced too if found to be faulty, don’t ever take the factory TDC marking for granted, check and confirm everything is truly relative to No.1 cylinder/piston position.
Build up is a slow process, the job start to finish including the head work is in the order of 20hrs hard labour.
There is one detail to tackle before the rebuild, certainly before the inlet manifold is replaced, and that is to replace the three small rubber breather pipes and non-return valve to one side of the supercharger (Kompressor). These pipes form a valuable part of the crank case/vacuum system and because of their location, heat plays a large part in their failure. Once they become aged they perish and split allowing an imbalance in the sealed crank case to inlet system. It has been challenged that even the slightest leak in these pipes can cause extra stress on the electronic VANOS Variator sprockets constantly trying to compensate for variance in induction air, adding to the impromptu wearing of the valve train mechanism and chain. I have no proof that this is the case, but it sounds most feasible – see here.
Sure enough the upper of the three pipe set was split, so all pipes replaced before the rebuild of covering components took place. Common sense says replace these as a matter of course whilst visible, as they are placed deep under the inlet manifold and supercharger body, never to see the light of day.
Vent Hose: A 271 018 12 82
The 2 hoses below the Kompressor.
Hose: A 271 018 15 82
Check Valve: A 271 018 03 29
Hose: A 271 018 14 82
Eventually the job was completed, key turned with trepidation, but bursting into life and a running engine resulted, actually sounding far better than it had for a few years!
I have not bothered in this case to write a step-by step account of the above job, only you will know if you are competent enough to tackle it! If you are, it is not overly complex, just a very, very time consuming job to do right – I am sure if you do decide to jump in, then you will manage admirably, calling on a set of skills built up over a few years of ‘playing engines’ to this level – its not for the faint hearted!
For the most, to rely on garages, dealers or independents to do this work for you would likely result in a very big bill indeed and it is easy to see why some folk just ‘put it all down to experience’ and scrap the car, never to buy Mercedes again – you can’t really blame them – M271 engine – bit of a lemon by all accounts!