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Re: Cold engine noisy[700/1990] posted by abe crombie on
Tuesday, 29 December 1998, at 6:57 p.m.
B230F engines are built to have low internal friction.
One of the ways to accomplish this is to control the fit of the parts so as to lower contact friction.
An area where this contact friction is typically high on any engine is the skirt of the piston. As the piston goes up and down, the piston sides below the wrist pin will scrub the cyl walls creating friction and wearing the skirt area. To remedy this the pistons are made somewhat oval in the skirt area at room temp and then the piston expands unevenly as it reaches normal temp. Since the piston is more narrow in the axis where it will expand the most, the piston ends up almost perfectly round and the contact on the cyl wall is spread over a larger area and friction and wear is minimized.
Okay, what this means is that the piston is looser when cold in one direction and the piston will knock a bit. In 1990 they made the rods heavier and this made the noise louder.
IF it goes away after engine reaches normal operating temp then there is nothing wrong whatsoever.
Some tolerances were adjusted on later motors and then tend to not have this noise.