Quote:

Walnut shell blasting to remove carbon buildup on valves was used extensively by BMW a couple of decades ago.

The walnut shells are organic and burn. They are softer than the metal so they can't damage it, but harder than the carbon deposits. Anything that doesn't burn when the engine starts up again, gets blown out of the chamber.

There isn't a downside to doing this. The upside is depending on engine controls, it may result in increased mileage. It will for sure increase power to pre-buildup levels.

R.



BMW still uses it. Still have problems. Valve stems leak oil.

Just saw techs at a BMW dealership using one today.