M274 vs M271

[simonjamesturne]

Hi, I'm trying to establish what changes were made when the M271 was superseded by the M274. I know the M274 still has a simplex timing chain, but I understand that it was changed from a roller type to another type to stop the stretching problems?

I'm I correct in this, and did it work?

 

[grober]

There were several significant changes in the M274 compared to its predecessor resulting in a 16% reduction in crank frictional losses and 9% reduction in timing gear frictional loses. This in part due the adoption of a new lanchester balance shaft assembly. Notable also was the adoption of Camtronic on the inlet camshaft best explained as switchable alternate cam profiles AUDI and BMW have similar tech see this treatise:-
http://schmidt-cnc.de/media/files/MTZ-Beitrag-Die-neuen-Ottomotoren-en-EN.pdf
and video

[YOUTUBE]Ks76D_EVfBE[/YOUTUBE]

 

[simonjamesturne]

Timing chain

They certainly mention that timing chain losses have been reduced, but noticeably fail to say if the design of the chain has been changed from a roller bearing chain to a different design. Maybe they didn't want to draw attention to the failures of the previous M271 simplex timing chains.

Some photos of the M274 engine seem to indicate that they moved to an 'inverted tooth' chain with this engine. Does anyone know if this is the case and does it help?

 

[190]

I've only seen the pdf above. One thing you do get from that is the balancers are now gear driven which is one less costly to replace chain. I don't know about the M271 but the V6 M272 did have a bad reputation for problems with the chain driven balancers.

I was quite thankful that the 1.6L version of the M271 in my C180K BE doesn't have balance shafts at all which seemed the best solution to the problem.

 

[190]

Some photos of the M274 engine seem to indicate that they moved to an 'inverted tooth' chain with this engine. Does anyone know if this is the case and does it help?

Looking again at the PDF I'd agree that the sprockets do look as though they might be the inverted tooth chain type. If so, they are much more durable than roller chains and have been used in motorcycle engines for many years as primary drive chains often positioned in the centre of the crankshaft where maintenance is all but impossible.

The double rocker pin type of inverted tooth chain is very efficient which given MB's claim for reduced frictional losses does seem to add up. You'd have to wonder whey they haven't been used more often but I guess the reason is higher cost.

 

[simonjamesturne]

Thanks for that. It seems also that the later versions of the M271 also have an Inverted Tooth chain. (the M271 EVO specifically). All the reports I see about M271 chains appear to show the old roller chains, so I wonder if using Inverted Tooth chains has stopped the chain stretching and sprocket jumping problems?

 

[190]

This describes the M271 EVO as having a newly developed "toothed bush" chain for the camshaft drive and a "simplex bush" chain for the balancer shafts.

I'm reading that as a an inverted tooth chain for the camshaft and normal roller chain for the balancer shaft.

http://autocats.ws/manual/sdmedia/mediadb/mb_Acrobat/einf/m271/2009_05_001_001_en.pdf

 

[markjay]

As far as I know the issue with the M271 engine was not simply that the single chain design allowed the chain to stretch - this in itself is an well known issue with all single-chain engines for many years now, and usually manifests itself as a noticeable rattle from the front of the engine (i.e. from behind the timing chain cover - for engines with the timing chain at the front) long before the chain stretches enough to actually jump a tooth and cause timing issues. Also, this issue is partially mitigated by use of automatic chain tentioners.

Instead, the specific issue with the M271 engine was that the timing gear itself - i.e. the sprocket wheels fitted to the front end of the camshafts - failed due to premature wear, causing significantl timing issues, and in some cases followed by terminal engine damage when valves met with pistons.

There are modified aftermarket sprocket kits avalaible for the M271 engibe, made of tougher metal, that do not suffer from this premature wear issue. It would be interesting to know if the sprocket wheels fitted to later M271 engines such as the EVO have been modified or not, and obviously whether the M274 sprockets suffer from the same issue.

 

[markjay]

As for the M271 engine timing gear failure issue, my understanding is that it was actually caused by a combination of three factors:


1. Stretched single chain causing higher friction with the sprocket wheel.

2. Sprocket wheel inherently prone to wear.

3. Poor maintenance - i.e. too long intervals between regular engine oil and filter changes, or use of low quality or non-MB spec oil, which reduced to lubrication properties of the oil and the point of contact between the chain and sprockets.


So this failure is less likely to occur on cars that have been properly serviced using appropriate engine oil and filter.

The issue is that the M271 engine was available on many entry level Mercs, which would have depreciated quite quickly and were well into banger car economy when passing the 100,000 miles mark.

The potential issue with a car bought for cheap by an owner looking for motoring on a budget is that regular servicing at a reputable specialist using MB-approved oil is in many cases the first causality of budget motoring. And from here it all goes downhill. Including the timing gear on the M271 engine.

 

[simonjamesturne]

Thanks for the info. I'm looking to move from a W211 270CDI, which I've had for 13yrs and 180,000 reliable miles, to a petrol and am concerned about engine longevity.

I wouldn't have considered the earlier M271 but am looking at an E coupe with an M274 to again keep for 10-15yrs. Simplex timing chains are a worry to me over the long term, which is why I won't consider a diesel OM651. If the petrols are still not longterm reliable then I guess I'll stick with a diesel OM642 V6. It's a difficult call for the long haul?

 

[190]

Given the inherent wear problem with the chain and sprockets it's interesting to speculate on best choice of oil to keep it at bay.

Obviously regular oil changes with approved oil but MB are not specific on the oil grade to use. In most climates to meet 229.3 or 229.5 for the M271 it comes down to a choice of XW30 or XW40 oils. I doubt it makes any difference whether X is 0W or 5W but When the oil is hot a 0W40 or 5W40 should provide a better oil film thickness for the chain. Rightly or wrongly I use that logic in my preference for 5W40.

MB are also happy for you to use a low saps 229.31 or 229.51 even though a low saps oil is not needed. Is that better or worse for the M271. I've no idea. I suspect an MB serviced car will only get the low saps version as that is all they will stock in order to have a common oil suitable for cars with DPF's.

 

[simonjamesturne]

Interesting, but I note that the M271 and M271 EVO call for the same spec oil even though they use a totally different type of timing chain. This suggests that the oil is speced for the bearings rather than the chain.

I also noted that although inverted tooth chains are stronger, they are generally used for very short runs where at least part of the run is submerged in oil (as in a motorcycle). Hence I'm beginning to think that the inverted tooth engines may in fact suffer from the same problems as the M271 in time. This doesn't bode well for the future longtivity of the M274 engines?

 

[grober]

Some more technical data on the M274. As a general note, these engines are increasingly complicated. I'm not sure if chain wear at high mileage is going to be the most likely repair required??
http://autocats.ws/manual/sdmedia/mediadb/mb_Acrobat/einf/204/2012_03_001_003_en.pdf

 

[simonjamesturne]

Yes I tend to agree. These engines don't look like they are going to be capable of the 200,000+ miles the old OM647 in my W211 can make.

I think I'll end up with the OM642 diesel V6 instead. I had hoped to get a modern petrol rather than an old tech diesel, but at least I'll know that it can get at least 150,000+ miles.

 

[ernie]

Thanks for that. It seems also that the later versions of the M271 also have an Inverted Tooth chain. (the M271 EVO specifically). All the reports I see about M271 chains appear to show the old roller chains, so I wonder if using Inverted Tooth chains has stopped the chain stretching and sprocket jumping problems?

A couple of 'Indys' on t'other side have recently posted about cam gear wear problems on the Inverted tooth chains on the later M271 204s. One of them has downloaded a picture that shows metallic particles all through the oil filter, so I don't think we've seen the last of these problems.

Ernie

 

[grober]

A couple of 'Indys' on t'other side have recently posted about cam gear wear problems on the Inverted tooth chains on the later M271 204s. One of them has downloaded a picture that shows metallic particles all through the oil filter, so I don't think we've seen the last of these problems.

Ernie

Except that the M274 AND M270 [ transverse orientation] in 2 litre form at least have a different balancer shaft cassette and other timing chain differences which one would hope may have allievated the problem somewhat in the later design engines?

 

[simonjamesturne]

Having read the reports I can't see any reason to think that the M274 engines are going to be any longer lasting than the M271 engines. Such a shame, but then again I guess Mercedes are designing them for a given expected life of around the 120,000 miles that most of these low end cars actually reach before being scrapped off as a banger.

 

[190]

I think there is a great irony in all of this.

Once upon a time engines had duplex timing chain that gave no trouble. Then most manufacturers went to belt drives which were quieter but needed changing at typically 60,000 miles. Replacement was relatively easy and cheap and at least on rear wheel drive cars.

Belt drives became frowned upon and the media encouraged us to look for engines with more durable cam chains. But they still need changing at 60,000 miles and it's not easy and it's not cheap and the engine can still fail expensively.

You have to wonder where the progress is.


It will be disappointing if MB has made a hash of the inverted tooth chain drive because the technology is well proven with many Japanese motorcycles having inverted tooth primary drivers that are very reliable.

Note that the M274 has gear driven balance shafts which is good but an inverted tooth chain driven oil pump. If the oil pump fails it will scrap the engine !

 

[grober]

Recalibrated engine longevity is perhaps an aspect of modern car ownership we have to come to terms with. Increasing demands by the environmental lobby have dictated modern power plants both diesel and petrol have to go to complex lengths to achieve emission levels and better fuel consumption. In the main this has involved complex designs and ancilliary parts tacked on to the basic internal combustion engine. Variable valve timing and cam profiling, variable oil and water circulation in the search for more rapid engine heat build up, exhaust gas recirculation, variable inlet manifold flaps, direct petrol and diesel injection, engine size reduction accompanied by supercharging or turbo charging to maintain power levels, air and water intercooling higher compression ratios , multiple valves, balance shafts, lower friction valve gear including chains, diesel particulate filters, adblue urea injection, catalytic convertors,complex canbus engine management electronics the list goes on and on Its possibly no wonder these engines are requiring work after the 100,000 mile mark or in many cases before that particularly if their servicing schedules are not adhered to.
In the interests of balance it should be pointed out that the other prestige German car manufacturers are similarly afflicted and jumping ship from MB to Audi or BMW is merely going present the owner with a different set of engine problems.

 

[simonjamesturne]

I agree, the OM642 appears to be the last of the "designed to last" engines, with duplex timing chains etc.....

My friends tell me that I'm bit of a dinosaur myself and that no one keeps a car 10-15yrs any more. In fact I'm told that the whole idea of saving up and then buying a car so that you actually own it outright is old fashioned.

Still old habits die hard, so I'll be buying with an OM 642 V6 this time, that will do me for the next 10-15 yrs just as my W211 has for the last 13 yrs.