info on gears:
The oil pump pulley bolts have a reputation for shearing off usually resulting in a broken belt and consequent top end damage. Whether this is due to an over-tensioned belt or to an under-rated or over-torqued bolt is open to debate. In any case, they should be replaced with new bolts at each timing belt change. [Karl-Dieter Haugk] The replacement bolt is Volvo p/n 948472, an extra strong metric 10.9 class M10 x 1.5 mm (standard thread) x 30 mm long bolt including a flat washer (Volvo p/n 960148). This appears to be an upgrade from the original class 8.8 25.4 mm long bolt which should reduce or eliminate the incidence of failure. Use the new, higher grade bolt as this is a critical engine part.
B234 Oil Pump Pulley Backside
Oil Pump Bolts. [Erwin Yu] When you order the oil pump pulley bolt from your Volvo dealer with the correct (according to FAQ AND dealer part guy)part number 946472, thinking that you will pick up a class 10.9 M10x1.5x30 bolt, you're wrong. What you will get is the same old class 8.8 bolt everyone is warning you not to use. The invoice that come with your bolt will say part number 982817 for only 98 cents.
What options do you have? Luckily, Fastenal ordered me the good quality bolt. While I'm there, I decided to order and replace all the other bolts too (2 cam pulley bolts, two idler bolts, all class 10.9): you can order them from their website. [Dave Stevens] You should be a bit concerned about that bolt. First off, we're talking about the serious M10 bolt that holds the oil pump pulley in a 16-valve engine, not the wimpy little bolts that hold the water pump. The torque spec for the oil pump pulley bolt at 40 ft-lbs (actually 15 ft-lbs plus a further 60 degrees) is basically torque to yield. Over-torqued or re-torqued and a standard grade bolt (class 8.8 metric) would be prone to sheering from metal fatigue. That's why a class 10.9 metric bolt is now called for. Thread locking compound (red Loctite) is also called for as the pulley turns in the direction that would tend to loosen the bolt, but it's hard to imagine that happening if the bolt is anywhere near properly torqued. Although having that oil pump pulley bolt sheer was not a common problem in the first place, it was something to be avoided as expensive top end damage was the result if it ever failed (remember that the B234F is an interference engine). Furthermore, the problem was likely more prevalent in the original 1989 (and possibly early 1990) B234Fs with a manual T-belt tensioner rather than the later B234Fs that used the automatic (hydraulic) tensioner that Erwin has where the belt is not easily over-tensioned.
Remove the oil pump pulley itself and carefully inspect for any signs of damage. You can make a special tool to assist in removing and reinstalling the pulley and bolt. These pulleys have been known to self-destruct, again, probably where the belts have been over-tensioned. In particular, look for signs of stress fractures on the back inside of the casting where the sidewall meets the face. Replace the oil pump pulley at the first sign of a problem.
Re-install the oil pump pulley with the new bolt and washer. Use a little Loc-tite and torque to 15 ft-lbs (20 Nm) then angle tighten a further 60 deg. A one step torque to 40 ft-lbs (55 Nm) should also be adequate, just don't over-torque. You can restrain the pulley using the Allen key method described above.
6.Loosen the balance belt tensioner pulley (lower left -exhaust side). Turn the hub to loosen the belt and remove it. Clean, spin and check all idlers for bearing wear.
https://www.volvoclub.org.uk/faq/B234Ftimingbelts.htm