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I don't know if CW will read my response to you, but I hope he does.
The B230 engines are very untolerant of excessive piston to cylinder clearance. This is due to the short piston design and how the piston clearance (or lack thereof) keeps the connecting rod centered on the rod throw of the crankshaft. Have you ever looked at the connecting rods installed on a B230 engine? There is considerable clearance between the sides of the connecting rod and the crankshaft. This is the big difference between the B230 engines and the earlier B23/B21/etc. The B23/B21/etc engines have a precision fit between the sides of the connecting rod and the crankshaft.
One of the mechanics at my favorite independant Volvo shop, MVP, had an engine overbored for use in his wife's car. The engine has piston slap noise. The mechanic told me the piston to cylinder wall clearance is within limits, but at the maximum allowed. That is probably the cause of the noise in CW's car.
The noise is not from the synthetic lube. Two of our B230FTs use synthetic lube (Amsoil) and have no piston slap noise. It is possible some noise is generated at under cold start comditions because the synthetic lube is thinner than dino oil at the cold temperatures when piston to cylinder wall clearance is greatest.
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