A while back I replaced my water pump and that pesky indicator/pointer for the timing marks on the shaft pulley was in the way. So of course I looked at it real close and removed it thinking that I could get it back in the same place no problem and anyways I wasn't going to want to use it till way later.

Well its later . I was pretty confident I got it back in position at the time but now that fuzzy memory is making me wonder.

I saw some posts about using a tool in the #1 pre-combustion chamber hole with a dial indicator to tell you when the piston stops moving (at the top) and some clever descriptions of doing the same thing with a sight glass and some oil in place of the tool and dial indicator (without having to remove the chamber!?)

When I was looking at 603.970 start-of-delivery documents using a digital tester I realized there must be a TDC nub/pin on the shaft pulley of my 603.971. Is there any way I could use that nub/pin to validate the pointer?

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1992 300SD 140.134 Sold

Is the nub pin located across from the OT= Top Dead Center on the degree wheel?

Member stretch suggested another way of checking for TDC but it takes more courage. In your case you would get the Piston close to TDC say 5-10 degrees before top dead center (you inaccurate point ought accurate enough for that) on the compression stroke.

Then you remove the valve spring retainer and valve springs and let the valve go down till it contacts the top of the Piston Head then you set up your Dial indicator so the plunger is on top of the Valve Stem.
As you rotate the engine in the direction of rotation the Piston + Valve rises the indicator needle moves and right when the needle stops would be TDC.

Member Stretch posted on the above long ago if you can find the thread he posted in.

Lining up the camshaft timing marks also gives you a rough estimate of TDC.

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84 300D, 82 Volvo 244Gl Diesel

Soon as I get a full weekend I'm gonna check... working dark to dark right now.

I'd have to remove the camshaft for that? Does the valve go straight down towards the piston or at an angle?

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1992 300SD 140.134 Sold

As far as the camshaft issue I am not familiar with models newer then 1985. I have never seen a Diesel Engine with anything but a flat cylinder head deck but that does not mean it is impossible for one to have angled valves.

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84 300D, 82 Volvo 244Gl Diesel

A couple of alternative methods from the gasser world.
https://dannysengineportal.com/top-dead-center-tdc/

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022