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It really depends on how or who did the rebuild. If Volvo did it, and the cylinders were honed in the factory cross-hatch pattern, no break-in should be required. It is also important that the rings get seated in the cylinders before assembly to minimize an initial break-in. Volvo uses closely matched piston clearances so the seating of the pistons/rings in the cylinders are well fit before any friction takes place. A good crank balance will help a lot.
I have a nice video tape from Volvo on exactly how they do their engine rebuilds. It tells a lot and explains why the engines last a long time compared to other rebuilders.
If you did a cylinder hone with conventional methods and loose fitting pistons, the break-in could take some gentle miles before the rings seat properly. A good start to break-in is take the engine from idle to ~2500 rpm slowly through the gears up to about 50 mph for the first 500 miles. Change the oil then repeat the smooth rev's to 4000 rpm up to highway speeds to 1500 miles then change the oil again.
The initial break-in will set how the engine likes to rev, and depends on how it's set-up and how you want to drive it. For a hotter cam you may want to keep the break-in rev's up to the cam peak rpm's where max hp is achieved. For a stock M cam, you may want to keep the break-in rev's lower to drive at a constant 1600-2200 rpm and just toodle around.
Good Luck!
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'89 245 Sportwagon, '04 V70 2.5T Sportwagon
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