MG Car Repair: rod bearings, piston slap, rod bearings

Question
Howard;   On cold start-ups my 1970 mgb has noisy rod bearings for the first few seconds. Will a 20-30% addition of Lucas to the engine oil or the addition of ZDDP help this matter out or should I be looking at a rebuild and if so how far should I go with the rebuild?  Car works great. good compression and oil pressure otherwise.  Thanks Terry

Answer
Hi Terry,
First look at the oil pressure after driving for a while and the oil is hot. It takes a little longer for the oil to heat up then it does the coolant so get the oil hot. Note the oil pressure at idle and at 2000 RPM. If you have 30+ PSI at idle and 55 to 75 PSI at 2000, you don't have a bearing problem. (with 10 or 20W 40 oil)

As for the noise you should let a experienced MG mechanic listen to it too. Because piston slap can make noise at the same time sequence. (cold engine)

Here is a major possible. BLM in their infinite wisdom (or lack of) put a filter system on MGBs with the filter loaded from the top. Even though they had a tube sticking up into the filter to prevent all of the oil from draining back, you still got a cold start knocking EVERY time you cold started the car.

If your oil pressure is ok or even marginal, and you have this "UPSIDE-DOWN" filter system find a local British car specialist and find the filter block that loads the filter from below.

I am not familiar with ZDDP but I do know that STP Oil Treatment works some.

Howard