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Old 08-01-2005, 07:31 PM
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Join Date: May 2005
Posts: 992
need help finding top dead center....

m103/w124 88 300e

1. we broke the plastic timing chain guide so i had to tear down the front of the motor....

2. we have replaced it and now with everything disassembled i am looking for top dead center.... is it the dot on the vavle cam or is it the notch...

also is it the notch pointing up on the crank....
Is TDC the number one pistion at the very top?

I am just checking myself.... thanks...

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Old 08-02-2005, 09:04 AM
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TDC is indeed number one piston at the top. This is true on any engine. The mark on the harmonic balancer should be very clear as to TDC. There is a small line cut into a washer or the cam itself that aligns with a mark on the front cam bearing cap.

So, there are two TDC positions for number one. One of them will cause the notch on the cam to align with the mark on the cam bearing cap and the other TDC position will not allow you to see the cam mark.

You really should find a book with some pictures. This is far too important to not have exactly correct and I meand EXACTLY correct. If the cam is advanced by only one tooth you can bend valves.

The way to put it together is to put the number one piston at TDC and then turn the cam so it will be in proper position for TDC and then slowly start tightening the cam bearing caps a little at a time. In other words, don't tighten down one cap all the way before touching the others. Start the bolts for all of them and turn the bolts on each one a little, then go to the next one and so on. If you don't bring the cam down in the correct position and gradually you can break the cam, strip cam bearing bolts or contact pistons with valves.

Good luck,
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Old 08-02-2005, 06:55 PM
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Join Date: May 2004
Location: New Zealand
Posts: 160
find it

A simple but not very accurate way is to put your finger in number one cylinder spark plug hole and turn over the engine by hand. When you stop feeling compression and start feeling suction, the piston has just gone past TDC. You can also sit a length of stiff wire on top of the piston and use the same idea.
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Old 08-02-2005, 08:12 PM
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Join Date: May 2005
Posts: 992

i was not going to remove the timing chain or any thing on the front of the engine so i did not place at tdc on tear down... but i had to remove everything because of that plastic chain guide.... haynes does not sell a manual for 300e and so i bought a cd which had very few drawings and they were confusing....and hard to read... most of the info said to take tdc off of the timing mark which lines up with the sensor... well we had already disassembled the whole front of the after that point marks are few.... there is a couple of marks on the cam and the quesiton is which one... the drawings all seem to indicate a notch but the real tdc appears to be a dot... and on the bottom crank there is a notch that goes to 12 oclock.

so the top was all i was having problems with....

we started it but did not let it run but a second.... i need to put water and air filter on.. and tighten exhaust... so i will report again tomorrow...

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