New engine required!

[tolsen]

Too much oil burns valves. Just the way it is. Basta!

[Ocracoke]

Too much oil burns valves. Just the way it is. Basta!

OK then, I assume there is too much oil as a result of the rings failing? I assume that would be the case if the wrong oil/oil being too hot/coolant not being flushed (select any from the above) had been used/occurred in the engine? Wouldn't secondary cooling (oil cooler being the most obvious here) be useful? I grant, it is too late at the moment for the OP but would it be a recommended mod then for the 450?

[137699]

I know we have been here before (many times) but it's worth considering the differences between the standard petrol 450 engines and the Brabus 450/roadster engine which rarely suffers the same issues: - oil cooler - different piston rings - different spark plugs - super unleaded perrol - shorter service interval.

[Thrumbleux]

Oil burns, consumes oxygen which the Lambda sensor detects as a rich mixture so leans off fuel. Oil has lower detonation limit than petrol so when detonation detected ECU retards ignition timing delaying expansion (cooling) allied to a slower burning leaner mixture which exposes the piston to greater levels of heat which will expose the oil to a greater possibility of gumming in the ring lands - the probable start of the high oil consumption. A rather vicious spiral that leads to burnt exhaust valves due to the level of heat still contained in the exhaust gasses due to late combustion and expansion.
That's my theory.

I know we have been here before (many times) but it's worth considering the differences between the standard petrol 450 engines and the Brabus 450/roadster engine which rarely suffers the same issues: - oil cooler - different piston rings - different spark plugs - super unleaded perrol - shorter service interval.

The above includes greater resistance to detonation (higher octane fuel), tends to run at higher rpm (reducing time for heat to be absorbed by the piston, and reducing the tendency to detonation), cleaner oil (shorter service interval), and cooler oil (oil cooler) - none of which contradicts my theory.

[markinnz]

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The above includes greater resistance to detonation (higher octane fuel), tends to run at higher rpm (reducing time for heat to be absorbed by the piston, and reducing the tendency to detonation), cleaner oil (shorter service interval), and cooler oil (oil cooler) - none of which contradicts my theory.

So I read that as advise to "drive it like we stole it!" .. I can go along with that!

[Ocracoke]

So I read that as advise to "drive it like we stole it!" .. I can go along with that!

Not sure I read it like that. I read it as the higher octane fuel explodes faster, causing a higher rpm. Still, I know what you mean.

For a 600cc engine, refitting the pistons with Brabus 700cc rings isn't a option (is it?) and the 600cc Brabus engine was identical to the base engine (I think, sure someone here can tell me). Same with the spark plugs but would BKR6EK (not BKR6EKE) be an alternative (it was suggested to me but I had only changed the plugs the week before so not yet done that). An oil cooler is going on the car reasonably soon so that should help.

[Thrumbleux]

The Roadster runs shorter gearing meaning that at any given cruise speed in 6th gear it will be turning higher rpm than a fortwo but at lower load (torque).

Higher octane fuel does not 'explode'. The whole point of octane is to avoid explosions (detonation/knock/pinking).

600 and 700 motors have different bore sizes.

[Ocracoke]

Higher octane fuel does not 'explode'. The whole point of octane is to avoid explosions (detonation/knock/pinking).

Doh. You are, of course, correct. Does rather raise a question that if Smart recommend 95+ Octane fuel for a standard engine, shouldn't the knock sensor help with this? Of course, getting back to original point of this topic, a shorter service schedule with religious oil changes using the correct oil should stave this problem off.

Cheers for all the advice guys. I'll arm myself with all this info and take a trip to the garage that's looked after it for five years and see what they say. Will report back later.

Did the garage do the reconditioning of the refit engine or was it from another source? I guess they do change all 6 spark plugs, use correct oil etc when servicing it?

[Mad smart person]

Greetings Guys, OK, setting aside the causes of burnt valves, does anybody change their spark plugs by taking off the plug lead (with the correct-ish tool) then removing the plug and replacing it? Or, do they replace the plugs in the way I've described? 'Cause it my opinion that's why the valves are burning at a single point. If oil was the cause, they'd be burnt at various points on the valve. Plenty of engines are designed to 'use' oil in the combustion process and the Smart engine is no different. The 600 & 700 engines use different plugs but the 700 engines, 450 or 452, use the same plug. Try burning synthetic oil, no visible smoke but a very SICK smell. Now burn ordinary oil, blue cloud and an unpleasant smell. You'll know what I mean if you've ever been behind an outing of micro / bubble cars - you see the blue cloud long before you need to slow to 45 MPH. Most people I've seen replacing spark plugs are the 'wham-bang-thankyou-mam' types. And, in questioning those that have just had their engine proceeding on 1 or 2 cylinders, their spark plugs were replaced around 1000 - 2000 miles ago. Also, using the wrong oil WON'T help. If you'd like to prove me wrong, next time you replace your spark plugs, biff a hand full of sand down the hole, the engine WILL fail in very short time. Now, if you show me an engine that's failed due burnt valves before the plugs have been changed, at the correct interval, I'll eat my words.
Cheers, Ian.

[Kapt. Q]

My take on these 600cc failures are slightly different, yes the lack of the oil cooler does not help, but actually I think it is a combination of the way the engine is tuned (mapped) and problems with the shape of the combustion chamber. Having recently had the chance to look in a 600 with only 40,000 on it it was clear that although the bores and rings were in perfect condition and oil control was being achieved by the 3rd ring it was well on it's way to being clogged with carbon. Hard carbon of the type that sticks to the slightly porus surface of aluminium is a result of inefficient (poor) combustion. It is interesting that on the 700cc engines they changed the combustion chamber shape significantly (and the plugs).

Cheers!

So rings clog, oil control is lost, oil burns, plugs foul and valves burn. on some engines things are left to the point where plugs are fouled to such a degree that they cause detonation and then parts of the plug damage cylinder walls, pistons and head.

[Thrumbleux]

My take on these 600cc failures are slightly different, yes the lack of the oil cooler does not help, but actually I think it is a combination of the way the engine is tuned (mapped) and problems with the shape of the combustion chamber. Having recently had the chance to look in a 600 with only 40,000 on it it was clear that although the bores and rings were in perfect condition and oil control was being achieved by the 3rd ring it was well on it's way to being clogged with carbon. Hard carbon of the type that sticks to the slightly porus surface of aluminium is a result of inefficient (poor) combustion. It is interesting that on the 700cc engines they changed the combustion chamber shape significantly (and the plugs).

For a long time I have suspected bore washing with petrol on this engine. Entering such a small cylinder it has such a short path to the opposite side cylinder wall that it could arrive there while still liquid where in a larger cylinder it would vaporise.

So rings clog, oil control is lost, oil burns, plugs foul and valves burn. on some engines things are left to the point where plugs are fouled to such a degree that they cause detonation and then parts of the plug damage cylinder walls, pistons and head.

For sure a failed plug is the start of the end w.r.t. to detonation but I still think it is a more gradual process caused by reduction in overall octane rating due to the oil's presence. Not for nothing are the 2-stroke fraternity obsessive about running with as little oil as they can get away with. They want as high a CR as possible and no detonation.

Interesting all the talk of the 'correct' oil. Mine has run since its first service on a mineral oil that has never been assessed to be given an MB approval number. It passed its MOT with a 'clean' (MOT tester's word) emissions pass a fortnight ago and has just clocked 70,000 miles. While it uses some oil it has never misfired, lost power, or shown any other sign of needing a rebuild right now. If synthetics were everything what chance of my engine reaching 70,000 miles without rebuild when most running on synthetics have required a rebuild considerably earlier? This engine has fundamental problems. Mechanical and control strategy failings IMO.

[Thrumbleux]

Doh. You are, of course, correct. Does rather raise a question that if Smart recommend 95+ Octane fuel for a standard engine, shouldn't the knock sensor help with this? ?

Yes, the detonation sensor will retard the ignition timing if it detects detonation - but the delayed combustion leaves a considerable amount of heat in the exhaust gases (that had combustion commenced at the correct time would have been deployed in expansion (thus cooling) to drive the piston), a well known cause of exhaust valve burning.
The additional heat in the exhaust of a late burned charge should not be overlooked. It (high rpm retarding in ignition timing) is a technique employed by the 2-stroke fraternity as the speed of sound increases with increasing temperature thus a hotter exhaust extends their upper rpm power output. (Conversely - where possible - they cool the exhaust for lower rpm power).