[Mcp Dude]

Smart 451 Piston collision with spark plug?


I have Smart 2008 451. It all started with a blown engine. My mechanic replaced the engine with a used engine. It failed in under 100 km due to a bent valve. They feel the piston hit the valve. Maybe the engine was defective? The engine was replaced again with another used engine. Within 50km I got a check engine light. Misfire. The mechanic is telling me it is once again the piston hitting the spark plug. So now he is saying it is my driving style to blame. He says at the point of the misfire the engine was revving at 5500rpm which he feels is too high. For my part I just step on the gas!

Has anyone experienced something like this?
Any ideas?

 

[Gearhead]

In my experience, the only time I've had pistons hitting valves was when there was pinging or detonation (on other vehicles -- so far, not Smarts thankfully). A misguided ECU could lean-out the mixtures too much... You might check the O2 sensors, the IAT sensor (intake air temp) and the ECU itself. If you've replaced the engine twice and have the same issues -- it's sounding more like it's a control or fuel problem.

I rev my Smart to the limiter routinely -- it's boosted to 1Bar and has well over 60K miles of hard boosting. The gas engine in the Smart fortwo 451 is a high-stress engine, it's got piston cooling oil jets, forged rods and Kolbenschmidt pistons in it. It's pretty tough. I've almost tripled it's HP and it still runs like a clock... Hope this helps...

 

[Sensei Grant]

Piston to valve impact could happen (with a timing chain I wouldn't expect it to happen unless a valve is stuck open) but it should be impossible for the piston to hit the spark plug. The plug would have to be too long or the piston travel too high in the cylinder or there is something in the cylinder between the piston and the plug. I guess you could have carbon buildup on the top of the piston but whatever the case if your piston hit the spark plug, you have got something seriously wrong.

 

[Mcp Dude]

Piston to valve impact could happen (with a timing chain I wouldn't expect it to happen unless a valve is stuck open) but it should be impossible for the piston to hit the spark plug. The plug would have to be too long or the piston travel too high in the cylinder or there is something in the cylinder between the piston and the plug. I guess you could have carbon buildup on the top of the piston but whatever the case if your piston hit the spark plug, you have got something seriously wrong.

The mech it say it is not a timing belt problem and probably that is true as the engine is running smoothly. I guess that it is not impossible as it is happening; the question is why?? You bring up a good point though... It doesn't really make sense that the piston can move that extra distance and only under hard acceleration. ???

 

[Gearhead]

Damage to spark plugs is a sign of detonation/pinging. Valves impacting the piston can also be caused by detonation -- high gas pressures caused by pre-ignition behind a valve may prevent it's closing. Also, if the fuel mix is too lean, very high temperatures may cause the valves to "stick" in their valve guides with the same results (collision with the piston). Check your O2 sensors and ECU.

 

[Sensei Grant]

You said both valve and spark plug is it actually both or was it valve in the first replacement and spark plug in the second? If it is spark plug that would eliminate timing as it doesn't move. As I said, unless it's carbon buildup, (or something else in the chamber) the piston travel is too great. I can see if you had just enough wear maybe at the wrist pin or the rod cap that at high rev the piston could travel further than it would at lower revs. If that is the case it's just a matter of time till catastrophic failure. Do you know the sound of a rod that is knocking? I would hope that your mechanic does and has checked that. One last though did they rebuild the replacement engines or just pull them out of another car and put them in yours. Any salvaged engine could have been damaged internally but not show any external signs of the damage. If it was rebuilt and the head was resurfaced it is possible that it has valves and spark plugs too close to the pistons but that should not happen if it was done right. Also on a rebuild the rod bolts should always be new as the old ones can be stretched but again that is not an issue if it was done right. I would hope that it is carbon as that would be a fuel issue not a major mechanical problem resulting in yet another engine replacement. Have you seen what your spark plugs look like when you take them out? That could let you know about carbon buildup in the chamber.

 

[Sensei Grant]

I think someone has posted the pictures showing what spark plugs look like under given conditions. Anybody remember where that was. I'm on my tablet so I don't have search ability to look for it.

 

[Rustedwrench]

In my experience, the only time I've had pistons hitting valves was when there was pinging or detonation (on other vehicles -- so far, not Smarts thankfully).

I am sorry, but this makes no sense. Pinging or detonation is uncontrolled combustion event. Valves hitting pistons is a physical collision between the two parts due to a mechanical malfunction. One has nothing to do with the other.

 

[Rustedwrench]

Something fishy here. I do not think your pistons have been hitting anything. I think your mechanic has been hitting the bottle.

Three failed engines in a short period of time is not a coincedence, it is the effect of some external cause with some diagnostic shortcomings thrown in to heighten the experience.

 

[Sensei Grant]

Something fishy here. I do not think your pistons have been hitting anything. I think your mechanic has been hitting the bottle.

Three failed engines in a short period of time is not a coincedence, it is the effect of some external cause with some diagnostic shortcomings thrown in to heighten the experience.

I didn't want to go there with out all the details, but that thought occurred to me as well.

 

[Mcp Dude]

Something fishy here. I do not think your pistons have been hitting anything. I think your mechanic has been hitting the bottle.

Three failed engines in a short period of time is not a coincedence, it is the effect of some external cause with some diagnostic shortcomings thrown in to heighten the experience.

I think my mechanic is competent but is not a specialist in Smart cars.
The more I think about it the stranger it seems... As someone pointed out spark plugs don't move so what could be causing this? Surely there is really no scenario in which the piston should be able to hit the spark plug???

As I said before they feel it is over revving but that too doesn't sound that reasonable? As far as I know the computer will not let you over rev??

 

[jwight]

FWIW, the smart's computer will not let the engine over rev. Going to 5,500 rpm as mentioned in your initial post is still under the 6,000 rpm red line.

 

[jetfuel]

...even at 6500 rpm I'm not hitting anything.....

Jetfuel....no rev...

 

[GoFaster]

There is no chance of the piston hitting the (correct) spark plug on these engines. It's impossible. The spark plug is dead center in the deepest part of the combustion chamber. It should be several millimeters from piston contact.