Cylinder 3 cracked exhaust valve

[MartinVC]

I have a relatively new ( late 2018) A class A250 petrol. It started to develop mis-fire problems recently, then engine management light on and car going into limp mode on occasion. Diagnostics indicated a valve problem in Cylinder 3. After extensive labour it can now be seen that the exhaust valve is cracked. THIS SHOULD NOT HAPPEN IN A CAR THIS OLD AND LOW MILEAGE (UNDER 60K MILES). To compound the issue, Mercedes are out of stock for replacement valves throughout the UK and Germany !!!!
This means I am without a car for who knows how long.

1. This type of breakage shouldn't happen .
2. Mercedes should be able to supply spares.

The specialist diagnostics place I took the car to suggested this was not an isolated occurrence with these engines so I wondered if anyone else out there had any similar experience ?

 

[Uncle Benz]

Cracked pistons are more common on this particular engine. I haven’t heard of valve problems myself

 

[SL63 Mark]

I have a relatively new ( late 2018) A class A250 petrol. It started to develop mis-fire problems recently, then engine management light on and car going into limp mode on occasion. Diagnostics indicated a valve problem in Cylinder 3. After extensive labour it can now be seen that the exhaust valve is cracked. THIS SHOULD NOT HAPPEN IN A CAR THIS OLD AND LOW MILEAGE (UNDER 60K MILES). To compound the issue, Mercedes are out of stock for replacement valves throughout the UK and Germany !!!!
This means I am without a car for who knows how long.

1. This type of breakage shouldn't happen .
2. Mercedes should be able to supply spares.

The specialist diagnostics place I took the car to suggested this was not an isolated occurrence with these engines so I wondered if anyone else out there had any similar experience ?

Others will know far more than me, but I have heard this is a Renault engine, so a suitable valve might be available from them. Alternatively it is not that difficult for a specialist engineering company to make an engine valve, especially if they can have one of yours to copy.

 

[EmilysDad]

isn't there a pattern part available? The last valves I bought were from a local motorfactor

 

[MartinVC]

Others will know far more than me, but I have heard this is a Renault engine, so a suitable valve might be available from them. Alternatively it is not that difficult for a specialist engineering company to make an engine valve, especially if they can have one of yours to copy.

Thanks for the Renault suggestion which I’ll pass on to the mechanic. In terms of getting a copy made, you’d have to think Mercedes would be horrified to hear their customers being forced to do that. I mean why would you ever buy a Mercedes again. Do their customers service teams ever read these threads?

 

[SL63 Mark]

Thanks for the Renault suggestion which I’ll pass on to the mechanic. In terms of getting a copy made, you’d have to think Mercedes would be horrified to hear their customers being forced to do that. I mean why would you ever buy a Mercedes again. Do their customers service teams ever read these threads?

I restore old engines, so getting a piston, valve or liner made is no big deal to me, probably cheaper than a new new one, and much quicker than waiting for out of stock items. I have a lathe, so might even have a go myself.

I appreciate average MB customers may not wish to do this, depends how much you need the car.

 

[ajlsl600]

I restore old engines, so getting a piston, valve or liner made is no big deal to me, probably cheaper than a new new one, and much quicker than waiting for out of stock items. I have a lathe, so might even have a go myself.

I appreciate average MB customers may not wish to do this, depends how much you need the car.

Fair play to you. Someone "made" the origional. It's about material quality, engineering ability, and equipment.

 

[MartinVC]

So my garage are recommending replacing all the valves, using the logic that if one has split they all could go at the same time and so all should be replaced.
I'm not sure ...... Any views please ?

 

[BillyBoy]

Sounds like a reasonable suggestion. I would hazard a guess that the biggest part of the cost by a long way is the removal of the head to access the valves and reassembly after. Once those are done, then the cost of additional valves is not a great difference, and avoids the risk of another big cost. Same logic is often applied when replacing a pre-heater on a diesel engine, may as well do all 4/6 while at it.

 

[SL63 Mark]

Sounds like a reasonable suggestion. I would hazard a guess that the biggest part of the cost by a long way is the removal of the head to access the valves and reassembly after. Once those are done, then the cost of additional valves is not a great difference, and avoids the risk of another big cost. Same logic is often applied when replacing a pre-heater on a diesel engine, may as well do all 4/6 while at it.

If price is reasonable, and they are available, then go for it. Personally I would want the work to be carried out by a Mercedes independent specialist I knew and trusted.

 

[ajlsl600]

Get head off. Throw some petrol in inlet side then exhaust. If fuel runs past valves.,change em, or reseat . If nothing or just a slight spreading stain I wud not bother, it's not a racing engine. Or if not yet in bits(you say prob identified from diagnostics?) do a comp test. Go from there.

 

[alexanderfoti]

We have one in at the moment (M270 engine, A250 26k 2019). With the same issue, burnt exhaust valve cylinder 2.

Heads and valves on backorder globally. Has been sitting here with the head off for a month+. Reading up, the issue is much more common in the USA, possibly issue linked to poor fuel quality? The M271 engine is also susceptible to this when run on bad fuel (or LPG), and its a very similair engine.

We are replacing all valves on no 2 and the fuel injector, as this cylinder is much more carboned up. We are unsure of the history of this partiular car.

 

[ajlsl600]

More hassles.

 

[brandwooddixon]

There seems to be a common issue with these 3 cylinder engines, VW and Nissan have had similar issues with number 2 cylinder being the weak point. Are they the same engine, built under license?

 

[ajlsl600]

So my garage are recommending replacing all the valves, using the logic that if one has split they all could go at the same time and so all should be replaced.
I'm not sure ...... Any views please ?

Wud be interested to know fuel nossle, pointing in direction of cracked valve? If not sounds like heat dissapation issue or, if many cases? poss cyl head design?