Checking Top Dead Center - PeachParts Mercedes-Benz Forum

eastthop · #1 10-17-2007, 06:29 PM

I've just been thru the exercise of retrieving a broken glow plug from a 1983 300SD. After pulling the head, it was necessary to pull the threaded ring and pre-ignition chamber. Pictures will be available soon! Now I'm putting back together, and have the head on with bolts in, but not tight. I've returned the engine hoist to the wonderful neighbor who let me borrow it, but cannot now remember if the #1 cylinder is at TDC. I've read about the TDC whistles, but have only seen them in reference to gassers. Can one be used for a diesel? I'd like anything not to have to remove the head again.

pawoSD · #2 10-17-2007, 09:21 PM

If a glow plug breaks off in the pre-chamber can't you just pull the pre-chamber to retrieve it? Or did it break off in the head? I thought there were several ways of getting them out?

P.E.Haiges · #3 10-18-2007, 02:17 AM

eastthop,

Can't U check for TDC on the crankshaft pulley?

P E H

Ken300D · #4 10-18-2007, 10:46 AM

You have to get the right one of two different Top Dead Centers in order to time the camshaft.

I presume the camshaft was removed without lining up the timing marks first.....

Ken300D

Stevo · #5 10-18-2007, 11:03 AM

If you installed the head with # 1 piston at the top, and set the cam to its marks, you wouldn't know if that is the compression or not. It wouldn't make any difference except you'd have a 50/50 chance of the IP being 180 degrees off. So at that point the only way to know would be too pull the IP and set it at its marks, rotate the engine to (my 616 is 24 degrees BTDC), what ever yours is, on the compression stroke (cam lobes more or less up) and reinstall the IP. I just did this

eastthop · #6 10-19-2007, 02:35 PM

Initially the glow plug was wedged into the head, where I could not get at it. When I took off the timing gear, the timing marks on the camshaft were lined up. When pulling the head, I remembered the chain moving the pistons some. Now I can't remember if I moved them back. I'll try setting up on the crankshaft, and have retrieved the TDC signal calibration instructions.

eastthop · #7 10-19-2007, 02:41 PM

To PawoSD, yes there are multiple ways of getting a broken glow plug out without removing the head. You can search this site for them. It concerend me - I'm not that mechanically inclined, but inspiration and perspiration overcame my fears. Also a little Jack Daniel's. I didn't have the $2600 set to extract teh plugs, but I was able to get the plug out with a lot of work. Most of the work was because I was unfamiliar with the particular engine I was working with. But now that I've done it, little else with this machine will scare me.

P.E.Haiges · #8 10-19-2007, 02:48 PM

eastthop,

If haven't rotated the engine more than about 45 degrees, U should be OK in bringing the crank back to 0 degrees and the IP will be in the correct position.

Always turn the engine 720 degrees by hand after timing chain is split and replaced to make sure none of the pistons hit the valves. Best way to do this is to put a deep 27mm (1 1/16 in.) socket on the crankshaft pulley and turn with a ratchet wrench.

P E H

eastthop · #9 10-22-2007, 11:57 AM

From PEH's response, and additional searching of the forum, it looks like I need to line up the mark between the pin and 'zero' on the crankshaft, and line up the camshaft marks to get top dead zero, TDC. I'll remove the rest of the injectors, marking them, and setting them up for cleaning. I'll turn the crankshaft via the 27MM deep socket, while having a helper old the chain. After that, I'll set teh chain on the sprocket, put the sprocket on, tighten the bolt to 90n-m torque, and set the rocker arms back on. Or should the rocker arms be set before?

winmutt · #10 10-22-2007, 04:14 PM

My solution was max revving the engine until the tip went out the end

.... Easier to pull PC's and use a vac.

P.E.Haiges · #11 10-24-2007, 10:50 PM

easthop,

Probably best to line up the cam first, install the chain and then install the Cam followers (there are no rocker arms in a MB overhead cam engine). Have the cam lobes pointing up when U install the followers.

P E H