Hi Cuong,
Glad that trick worked. At least it's only rings and a base gasket you'll need, and nothing more drastic!
When was the engine last apart? It may just be that the rings are gummed up, and not expanding to fill the gap. Only way to check is to remove the barrel (leave the head attached - it'll save the price of a head gasket).
Let us know how ya get on...
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