Q&A

Misfiring

My Mini has a problem with a misfire on both cylinders nearest the radiator. Replacing the spark plugs produces an instant cure but only for a while, the misfire soon returns. The plugs from both cylinders become oily very quickly. Cleaning or replacing the plug cures the misfire temporarily. A friend of mine has suggested that there could be a problem with the piston rings or the valve guides and stem seals on the cylinder head. Should I remove the engine and have it rebuilt?

Jake Davey

Before removing the engine I would carry out a compression check to see if there is a big difference in compression between the pairs of cylinders 1 and 2 and 3 and 4 (1 is closest to the Mini's side radiator). If there is a difference it could indicate bore wear or a ring problem. You then need to