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This point is not specific to RWD.
However RWD Volvo is one of only a very few cars still available that has a non-interference engine in most models. (Exceptions: B230E engine type was sold outside North America and is an interference engine, as was the 16-valve red block used in a few 740s.)
Most engines today are an interference engine. If the timing belt breaks there is usually damage to the head (valves) and possibly to pistons. The red block motors in the RWD Volvos have a non-interference design and if the timing belt breaks all you need is a tow off the road and a new belt installed.
A non-interference engine has piston travel and valve mechanisms such that the highest point the piston reaches is not high enough to reach the valve's lowest point when it is fully open. So even if the belt breaks and the piston goes up when valve is fully open, they don't touch.
Most modern designs use an interference design to get more power from the engine.
In any case, for all cars you replace the belt at specified mileage intervals so it does not break (50K miles for most 240s).
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DAMHIK: Don't Ask Me How I Know! - - - Sven: '89 245, IPD sways, electric rad. fan conversion, e-codes, 28+ mpg - auto tranny. 850 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).
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