As Dingov70 says, the worry is that something has altered the timing by allowing the camshaft timing to alter relative to the crankshaft. This will take the pump timing with it. If the camshaft timing gets too far out, the valves will hit the pistons which gets expensive.
The crank bolt which secures the vibration damper to the crankshaft is a single use bolt and must never be reused. A new bolt MUST be fitted whenever it is disturbed. A genuine Volvo bolt, or one from any reputable aftermarket supplier will come with the diamond washer already fitted. Should you or your mechanic find this bolt is loose you can't just tighten it up again; it must be replaced. It's also VERY tight; 160NM + 180 degrees
If all is well on the cambelt side of things, then the problem is likely to be that the pump timing has shifted relative to the camshaft. This is much less serious since there's no great risk of damaging anything.
The main thing people sometimes find difficult about setting the camshaft timing is that there are no timing marks as such. It's not actually too difficult to do and there are a few good guides on how to do it and some useful videos on Youtube.
Something that may help your mechanic is that the D5252T engine is basically an Audi AEL engine with some Volvo specific modifications but setting the camshaft timing is the same process for both.
Assuming the camshaft timing is correct or has been put right then it comes down to setting the pump timing relative to the camshaft. Fine adjustments are made by altering the idler and tensioner positions on the injection pump belt and coarse adjustment is made by moving the injection pump drive belt pulley relative to the camshaft.
The pump timing is usually measured dynamically with suitable software but it can also be done with a dial gauge. If your mechanic has software that will read the pump timing it should be a straightforward operation.
If I as an average amateur can manage to do it, then a trained experienced mechanic shouldn't have any great difficulty. However he's wise to be cautious since there are one or two potential pitfalls for the unwary.
Hope this is of some help
Martin
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