do you have the 16 valve version of the engine? i believe the B230(8 valve) engine is non-interference should something relating to the timing and stuff go, but the B234 (16 valve) is not.

so, yes, if you have the 16 valve engine, it is dangerous to drive like that i think. i hope someone else confirms. but i think 1987 you have an 8 valve.

a harmonic balance (or crankshaft pulley), if you purchase from a place like www.fcpgroton.com (call them if it's not listed) will run you around $70 for just the part. it is basically a big metal wheel type pulley thing, as shown by www.newandusedvolvoparts.com in the included picture.

labor will probably run you about the same as or more than a timing belt job.

p.s. you might as well do the belts while they're down there. the belts themselves are cheap. may want to consider replacing the crankshaft (both the intermediate and normal one) as well as the camshaft seals.

expect to pay upwards of $250 give or take, not including parts. heavily dependent on your mechanic.
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Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'