Today, i heard this scary knocking noise again from my engine ( A15 )..it goes.."tong tong tong" whenever i rev the engine. This happened about 4 months back, just to find out that the piston rings were blown. I changed it to a good material' ring, and took good care not to over rev..
Now, its back again...and i noticed white smoke from my breather ( on rocker cover ), just like before...

Anyone knows why this is happening.

p.s : The rings are of good quality, the engine never overheats, engine oil maintenance is every 5k...and im running a good A/F ratio....

Are you putting them in right ?I'd say you are.

I'd say to little oil on the walls is doing this with would be from bearing clearance or rod side clearance.

I guess im sure the rings were placed in well. I didnt do it though. My 40 years experienced mechanic did it. Im confident of him. The engine has run about 20,000km already before the rings gave way.

**My prime suspect is that im still running lean...errmm, but plugs are ok, temperature is great too...what could it be then?...

detonation/pinging/pinking may be the cause. Do your spark plug ends look white? They should be tan. If they are white you are running lean, especially shiny white or with blisters is proof of detonation.

could be a combination of the clearnaces not right with lean running conditions. could also be too rich washing the bores with petrol and the rings binding in to bores.

Are the rings still intact when you take them out or missing or broken?

any lip on the bore?

The core of the spark plug is white, but not shiny. No blisters are visible.

By the way, i have not opened the engine yet. So, im not sure of the rings' condition.

hmmmm, dude, the sound you mensioned, is that piston slap?

Im takin a wild guess here, is the oil pressure ok? is the lubrication flowing well?
Maybe its excess wear. Im just takin a guess here.

if you havenot opened the engine up yet, do compression test, get some readings. sounds like worn bores and blowby to me.

Not sure of piston slap...

**I have another concern here.

All this while, my PCV ( positive crankcase valve ) breather - the air is directed to the atmosphere ( engine bay )...and the rocker cover breather is not connected at all.

Can this cause any problem?