To change the pump timer on a 617, you need to mark the chain and timer with a paint marker. Make SURE the marks are wipe-proof, you don't want to loose them. I assumer you still have the vac pump off. Collapse the chain tensioner (large rail on the right side) completely to get some slack in the chain. Transfer the slack to the IP side by rotating the cam sprocket with the bolt.

Hold cam timer against engine rotation and loosen the nut in the center, the slip a piece of sheet metal between the timer and the chain. As noted, you may need to remove another slide rail to get enough slack, but probably only on a new chain. Pull timer gently out, making sure you don't disturb the IP shaft too much.

On the bench, transfer the paint mark to the new timer by locating the Woodruff key slot and counting sprocket teeth so that the mark is in exactly the same relative position on the new timer.

Slide new timer onto the pump drive (have a care not to push the key out and into the chain case!) using the pit of sheet metal to hold the chain away from the sprocket. Align marks and pull the sheet metal out to drop chain onto the sprocket and pull the chain tight with the cam sprocket.

You should return the IP timing to exactly where ti was with this procedure, but it may not be a bad idea to check anyway.

Check the chain stretch, too, and if it is more than 8 degrees, pull a new chain after replacing the timer, THEN check IP timing.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!