VALVE TAPPING SOUND IF ENGINE IS COLD, RUNS SMOOTH WHEN HOT
December, 4, 2007 AT 1:41 PM
1990 BMW 525 V6 Two Wheel Drive Automatic 197000 miles
hi, I am very thankful for your good website. I could find lots of my questions answered. But this problem I have is kinda strange. I am pretty new with bmw cars. I recently have the valves clearance adjusted, and spark plugs, distributor and rotor replaced. In the morning, when I first started the car while engine is cold, I notice that the valve tapping noise is very distinct, and the car accelerates not as fast. But, when the car is warmed up after 20 mins of driving, the acceleration is great and tapping noise is hardly noticeable. Why is this so? Would changing the oil pump help? What can we do to improve the cold starting conditions?
Without being there with you it is difficult to speculate what the noise is that you are hearing. If after the car is warmed up and the noise is greatly reduced, I might speculate the noise as being something internal. My experience with the M-20 inline six motor in your car is that they are very robust and long lived if you maintain them correctly. As far as the performance matter, internal combustion engines are, from an engineering standpoint, heat pumps. The hotter they are, the more power produced, to a point. I feel your concern and since I sit in cyberspace, I am limited as to the advice I can give. Is the noise coming from the top end of the motor or do you feel it is deeper in the engine? It is not unusual for higher mileage motors to rattle a bit and if this is an internal engine noise, you have two choices,
1. Drive it and maybe use a higher viscosity oil(20w-50 is recommended)
2. Replace the worn components. If it were mine, I would drive the car and not worry about the noise.
Repost if you have further questions Dr. Hagerty
December, 7, 2007 AT 4:59 PM
I definitely agree that the hotter the engine gets, the more power the engine delivers. Yes, the noise is coming from the top end of the engine. It is the valve tapping noise. Initially, I had loud valve tapping noises all the time before I have the valve clearances adjusted. After the adjustment, the same tapping noises is gone only when the engine gets hot. If it is cold, I had to drive for at least 20 minutes before the valve tapping noise igoes away. During the first 20 mins, the engine does not have power when accelerating. It is like you step on the gas pedal, and find the engine struggling to increase speed. What problem could this be?
December, 7, 2007 AT 5:46 PM
If the technician that performed the valve adjustment has integrity and is good at working on BMW cars, return to them and state your concerns. If not then I would advise you that the valve adjustment was not performed correctly and that adjusting valves on an M-20 motor takes a fair amount of experience and is best not trusted to a non-BMW specific technician. Other issues that can affect power are throttle plate adjustment and it's state of cleanliness, the correct spark plugs(not platinum!)Properly gapped, fuel grade, fuel injector condition (are they spraying correctly), deposits that accumulate over time.