Received a call from a panic stricken friend of my youngest son. He thinks he may have moved the crank gear with the TB off on his 97 850 and might be 180 degrees off. I think there would be interference preventing the rotation to 180 degrees out, but I'm not 100% certain

Common sense would dictate that if piston #1 is at TDC and all timing marks are lined up, you're safe, BUT I need to be 100% sure that I'm correct before I call.

Are my assumptions correct? Thank you

Easy answer. Have him remove the spark plugs. Then with the Tbelt on, rotate the engine 720 degrees. If there is no resistance, then he is good to go.

If there is any resistance - STOP. Rotate the crank back to where the marks line up. Take the belt off and reposition the crank.

I hope he painted the mark on the crank to make it easy to align.

Klaus
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Volvos should be saved from the junk yards, not donated.

I believe that's why the index marks on the cams and crank aren't exactly at TDC. That way, during setup, none of the pistons are at the very top of their stroke, so the cams can be turned freely without fear of interference. At least that's what I've read over on MVS.

It matters not that the crank mark is not at true TDC, that is for timing and those that race these engines on a track. Us mere mortals just line things up and hope the engineers are correct.

The only way to check the possible movement of the crank with the belt off, is to rotate the engine with the belt on. Remember, if either of the cams is off by 3 or more cogs, valve damage will happen. If the crank is 180 off and the starter is engaged, you are looking at valve replacement.

Klaus
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Volvos should be saved from the junk yards, not donated.

Thanks Klaus,

I passed the info on and it turns out the crank was rotated 180 degrees. The young man felt resistance while hand turning the crankshaft bolt and immediately stopped, loosened the timing belt, rotated the crank another 180 degrees, put the timing belt on and rotated 3 full rotations without resistance. Everything was put back together and worked out OK. Thanks for your assistance.