Reaching 97,000kms (around 60,000 miles), I take my R56s from the airport and drive via highway to my place. I am speeding (a little bit) and suddenly I feel a hickup and after a couple of minutes the engine lamp goes on.
I stop immediately and I notice that the engine is bumpy, like one cylinder is not working. Idling is also hard. Restart the car and everything is fine. Some days after that, the engine lights comes in again, this time it doesn't go off after restart. Hard idling and not smooth operation as well. Plugged it in my OBD and I read misfires in cylinders 3 and 4.
The next day, the car is being towed to my mechanic:
- Melted spark plug
- no compression at cylinder 2, caused from either a burnt valve or a burnt piston. I don't know yet, tomorrow he will start stripping the engine down.
He told me that there was a lot of carbon deposits and given that I had the valves cleaned 30,000km ago, he suggested not to drive the car so calmly, as this could have been the source of the problem.
What do you reckon?
Spark plugs were 5,000km old. Car properly maintained (oil change every 5,000km with top quality liqui moly top tec oil). Oil consumption has been minimal (200-300ml per 1,000km). Use of high octane gas.

If it's a burnt valve, my technician will repair all valves and valve seats and will do some work on the engine cover as well. If the piston is burnt, then he suggested a full engine rebuilt with material of higher tolerances...
I will repair it under any case, however, the question is whether I will have to proceed with other expensive repairs in the next 3-4 years that I intended to keep the car.

 

Most likely a valve, a somewhat common problem on these cars..

 

Burnt valve is common, I rebuilt one two years ago, not your average job, but the outcome can be quite rewarding if the job is done clean. It's like a brand new motor because I've also cleaned out the piston's top side during the rebuild. With new timing components and new valves, it warms me to know this build can go for a long while down the hatch.

Or you can look for an alternative where you locate a low mileage motor from a junk yard and swap it in. Cost will be similar either way. If you can manage the work on your own, then you'll be able to save half the cost. You mentioned you're wanting to keep this for 3-4 more year, that's enough reason to repair and keep it going in my book. After all, these cars are fun and rewarding to drive with, I would make such an investment.

If you don't repair, you'll likely need to rid it at a big loss where as no one will pay more than a thou to buy a mechanically inoperable vehicle. And if you repair then sell it right off, you'll come upside down quite easily given the age and the generation latency of this car. So I think it's worth it to repair and keep driving it for few more years, you can get more out of the whole ordeal that way.

 

Whats the typical cause of a burnt valve?

 

Carbon build-up from engine oil aggregating onto the valves. Once the carbon build-up gets inside the chamber and get on the chamber facet of the valve, it'll likely create a hot spot there and eventually lead to burnt valve due to excessive heating profile localized at the carbon-built up location.

Carbon build-up is inevitable on direct injection engines unless there's an added injector on the port side of the intake valves to keep it clean. Many manufacturers have mitigation features either by adding that extra injector or by lessening the amount of oil entering the intake manifold from crank-case ventilation. So far, no one can escape the eventuality, still. It's a curse of direct injection engines, but these engines do bring better power and fuel efficiency to the table.

 

Thanks Yupetc,
Very clear response.
Indeed the mechanic told me that there was a lot of carbon deposits in the engine. The problem is that I had the engine cleaned with nutblasting and the BMW equipment 35,000km ago. Since then, I use only premium fuel.
Indeed the mechanic said that the cause of failure is me driving the car in low revs and not periodically stepping on it.
I guess I will need advice on how to do this once the car is repaired. Should I go with high rpms for a long time (i.e. on the highway for X kms), or is it a matter of doing constant and repeated accelerations?

The rest of the valves are OK and will not be changed.

**using top-tec liqui moly oil, changes every 5,000km.

 

No type of oil or fuel will help you mitigate this problem and for our N14 engines, it's very quick to aggregate oil onto those valves. I have my own walnut blaster kit and I do this for MINI, BMW, VW, and Audi vehicles as a weekend garage work. On my own MCS, I basically blast the valves clean every 10,000 miles (16,000kms) and every time I do it in those intervals, those valves are all "wet" with oil, not gunked, but just wet with a slight carbon build up on the stems. The valve flap itself looks oily, not gunked. So if you do this walnut blast every 30,000 km, then I would suspect to at least see a slight bit of build up.

One common mod for our N14 engines is to install an oil catch can between the crank case ventilation and our intake tube. Doing so will minimize the oil entrance, it will not eliminate, but will lessen it by a great amount if you manage to install a good oil catch can. There are plenty of those talked about here in this forum, please go look them up.

Lastly, yes, if you drive spiritly on the high way you can help blow those carbon deposit off, but that'll require you to keep your engine speed above 4k rpms intermittently. There are many schools of thoughts on how to do this, but I myself like to drive fast, so when I go up the ramp, I floor it. When I need to pass other cars, I floor it too.

 

Italian tune up! A redline (or two) a day...

 

Once you get the valves cleaned, consider adding a Water / Methanol Injection system. This'll help keep the valve stems clean while adding a little bit of extra power. WMI will NOT clean up a set of dirty valve stems, it only helps prevent carbon build-up. Definitely add an OCC to the VC / Manifold port, preferably a dual OCC.

 

I also had #2 cylinder go out and it was in fact the exhaust valves. Did the top end rebuild myself.

 

Where's the Delete function for posts?

 

So... why own a car that requires this amount of bullshìt?

 

Great question. Probably because it is an oversized go kart that is fun to drive. Thats why i keep mine!