Question about finding top dead center. - PeachParts Mercedes-Benz Forum

dka-66 · #1 06-13-2009, 07:35 PM

I wrote this and it is kinda long because of the story and me being ticked off, The question is at the end of my post so you can skip the middle garbage if you want.

OK, I am so close to choking a relative but thank god only by marriage.... This person had offered to help put the 300TE (1989 with the M103) together and I was trying to keep him from touching it because even though he claims he used to work at a shop he manages to break everything and messing stuff up, Well I put the head on and torqued it down the other day and I had the crank set at top dead center and I had the cam set up in the correct position that was shown in WIS..... I did not the timing chain on yet and my brother in law decided he was going to turn the crank, I am sure he did this to screw with me (yes, he would do this).

So now I have a crank that I am not sure were it is set, can I use the old school method of a small diameter wood dowel through the spark plug hole and turn the crank until it is as TDC (or the whistle deal to find it).
These methods do not bother me if I am working on a my Mustang or my Air Cooled Volkswagen (1965 Sunroof beetle, just saying) but working on the Mercedes is a bit of a different experience, The WIS program shows a method were you have to bolt on a unit to the head with a meter and long needle like extension that you can confirm TDC.

Can I find TDC with the whistle tool or the old school dowel down the spark plug hole? would the results be close enough or do I really need the meter goofy looking thing so I can get it right to within a width of a hair correct?

JonL · #2 06-13-2009, 08:26 PM

Yes, you can use a dowel. Do you not have the crankshaft damper with degree marks on the engine?

ehopkins · #3 06-13-2009, 08:42 PM

Your OK!!!
Step 1:

Kick your relatives’ ASS then maybe he will get the hint to stay away. You can do this by yourself now that the head is on.

Is the chain on or off? If on I would take it off and start from scratch again.

I used a long thin screwdriver in the #1 cylinder. Again, may not be to spec but it worked for me. LOL A long wooden dowel should work fine.

Did you mark the rotor tip and the orange base behind it. I believe I mentioned it to you in an earlier post. That way you can turn the crank from up top and see exactly where you need to be. If not make sure you mark the balancer and turn it from the bottom. Once you start getting close switch to the top and do the final adjustment. If you go past your mark just make another full turn in a clockwise motion. DO NOT GO COUNTER CLOCKWISE. After you get to TDC go ahead and mark the rotor tip and that orange base behind it, then that way you have a reliable reference from the top.

dka-66 · #4 06-13-2009, 09:11 PM

I am ok on the head since I did not have the chain connected and I have a new rotor and orange thing and some other stuff because that is the stuff that he broke during disassembly...... I told him to wait because I was gonna run in side and do a search for a couple things to find out why things were being difficult to get off... I came out and he said "dude I already got it" I said cool and then I got the "yeah it ended up breaking but their out and those parts should not cost that much" That is when I got pissed and starting telling him off and that the "orange thing" that he thought was cheap is actually around 60 to 75 dollars, He gave me the "oh man, I'm sorry" no I'll pay for 'em or anything..... So I do not have those parts to check against.

JonL, I do have the crank shaft damper with degrees on it, but what do I line the degrees up to because I had to removed the TDC sensor which is adjustable so there is no reference mark to line it up against (or is there).

my main worry is the wood dowel or screw driver trick might not get it dead on, of course this is because I see the detailed way they do it in the WIS program and I am thinking that it better be spot on with no degree of error.

ehopkins, do live in Texas (maybe close to Dallas) because this person is my brother in law and even though my wife won't mind, heck even his Mom and Dad are pissed because some stuff that he had been doing so they would probably say he deserved it........ But I have a wonderful Nephew and Niece that my Wife and I love spending time with and if I kick his ass it will be a long time before we see them again.

cliffmac · #5 06-13-2009, 09:43 PM

so, take the chain off and reset the things (crank cam). If you can't do that then ....Oh Oh......good luck

JonL · #6 06-13-2009, 10:03 PM

If you are extremely careful, the dowel can probably get you close enough to put the cam sprocket on the right tooth. It would not be accurate enough to find TDC within around 3 or 4 degrees. There are ways to find TDC accurately without expensive tools, but a dial indicator is pretty much a requirement. On the other hand, I know a guy who can do it with a slip of paper.

I'm not familiar enough with your engine to know if the cam timing is adjusted with offset keys, and if that is part of what you are trying to accomplish. For that the dowel by itself will be inadequate.

You will also need to rotate the crank to TDC on the stroke that lines up the rotor with the number one ignition wire. You could be out 180 degrees on the rotor, in which case you have to rotate the crank another full revolution.

Again, not knowing your engine, I would think that there is still a reference mark on the timing cover someplace to align with the damper degree markings. The TDC pickup should be looking for a little pin or something, the degree marks are there for humans to look at, not sensors.

ehopkins · #7 06-13-2009, 10:17 PM

Quote:

Originally Posted by JonL

If you are extremely careful, the dowel can probably get you close enough to put the cam sprocket on the right tooth. It would not be accurate enough to find TDC within around 3 or 4 degrees. There are ways to find TDC accurately without expensive tools, but a dial indicator is pretty much a requirement. On the other hand, I know a guy who can do it with a slip of paper.

Haven't heard of the slip of paper to find TDC but, I have used a 2X4.

ehopkins · #8 06-13-2009, 10:36 PM

Quote:

Originally Posted by dka-66

ehopkins, do live in Texas (maybe close to Dallas) because this person is my brother in law and even though my wife won't mind, heck even his Mom and Dad are pissed because some stuff that he had been doing so they would probably say he deserved it........ But I have a wonderful Nephew and Niece that my Wife and I love spending time with and if I kick his ass it will be a long time before we see them again.

No, sorry I'm in Arizona. Maybe you can have a wrench slip out of you hand or something.

LOL

Yea, pricing all of the ignition parts on these cars are extremely expensive compared to domestic parts.

Best prices I seen are:
Cap - 91.43
Orange thing-a-ma-gig - couldn't find
Distributor Cap O-Ring Seal - 3.85
Rotor - 38.87
Wires - 142.00
Plugs - 1.58 ea
Coil - 74.82

dka-66 · #9 06-14-2009, 09:49 AM

Quote:

Originally Posted by ehopkins

Haven't heard of the slip of paper to find TDC but, I have used a 2X4.

A 2x4, please do tell......if your using these types of tools that is probably why you have that nasty gap on your head

getting the cam in the right position is not an issue since there is a tiny hole in the cam to line up against a cast mark and if the chain was on it would have been no problem at all.
I might research what I need and how much the cost is for the dial indicator setup that I need to do it properly, I can probably finf a bunch of other fun things to use the dial indicator for.

As far as a wrench or something slipping out of my hands and hitting my brother in law.... I will just say that I have a lot of experience with things slipping (or odd things happening) and hitting me that ends up with me in the emergency room, I have not managed to focus this amazing power on hitting other people though...... So that plan has a 99.44% chance of backfiring and harming me. The last time something odd happened I ended up at one of the best Ophthalmic Surgeons in Houston.

I would like to hear about this finding TDC with a piece of paper.

I could call my Dad in NY since he use to own a shop and is a great mechanic but he will give me a speech on how I should have taken extra precautions so that this could not have happened, I'll tell him it's not my fault and then he will say "yes it is because I did not take the extra precautions and take an extra 10 seconds to make an extra mark"

dka-66 · #10 06-14-2009, 05:04 PM

I found what I was thinking of and have two different examples which you are basically doing the same thing. This should get me really close to TDC.

Quote:

1. Make an indicator from some clear plastic tubing, a jar of light oil, and an old sparkplug.
2. Break up an old sparkplug and attach a length of clear plastic tubing to it (make it airtight).
3. Remove all the spark plugs.
4. Stick your thumb OVER the #1 cylinder spark plug hole. Rotate the engine (see note below on tricks for this) until you feel pressure on your thumb. That's the compression stroke. TDC is at the top of this stroke.
5. Screw in the sparkplug with plastic tubing attached and insert the other end of the tube into a jar of light oil. Continue rotating the engine. Bubbles will appear until the piston reaches the top of its travel. When it starts down on the next stroke, the bubbles will stop and oil will begin traveling up the tube. Stop at a convenient point and mark the tube. Then mark the crank pulley and the engine body at a convenient spot.
6. Rotate the engine backwards and watch the oil recede into the jar. Continue rotating. As the piston continues past tdc and downward it will again suck oil into the tube. Rotate the engine till the oil again reaches the mark. STOP! Mark the crankshaft pulley where it lines up with the mark you made previously on the engine. You should now have two marks on the crankshaft pulley. The midpoint of these two marks lined up with the mark on the engine is tdc. Whoa! Almost like finding South with a wristwatch. Boy and girl scouts listen up.

and this one

Quote:

Take an old spark plug and remove the guts (porcelain and middle electrode), then create an internal thread through the middle of the hollow spark plug or weld a nut (about 5/16 or 8mm) to the spark plug shell so you can thread a long bolt through it. Now install this new TDC tool into No. 1 cylinder (with bolt backed off).

This procedure works best if the chains are off. Loosen the rocker arm adjusters fully (you don't want to introduce valve head to piston), as you will rotate the engine around without the valves in synch.

Install the crank pulley and rotate the engine (CC or CCW) so the crank pulley TDC notch is about 1/2" or so from the TDC line on the crankcase (for No. 1 cylinder). Thread the bolt in by hand until the bolt stops against the piston. A nut snugged on the bolt helps hold this position. Place a temporary mark on the pulley opposite the TDC mark on the crankcase. Now rotate the engine (by hand) again in the opposite direction. As you approach TDC, slow down, then gently continue until the piston stops against the TDC bolt. You'll feel the resistance. STOP and again mark the pulley opposite the TDC mark on the crankcase. You now have two marks on the pulley. True, absolute TDC is exactly halfway between the two marks. Repeat as often as you like to validate. If halfway between marks happens to land on the factory notch, great. If not, create a new notch as this is your new TDC reference point for accurate cam and ignition timing. Paint it with white paint for visibility and don't forget to remove your TDC tool.

any comments are more then welcome.

JonL · #11 06-14-2009, 06:42 PM

I've used the liquid method on rotary engines that have no well-defined TDC (as in a true dead spot where the piston stops and reverses direction). You have to work quickly because there may be a tiny bit of leakage past the rings. There's also air that gets trapped, and the oil sticks to the tubing, and all sorts of things conspire to make you less than 100% certain about accuracy.

The bolt method seems like it would be very accurate and easy, provided the spark plug hole gives a good angle to the piston. Do this method only when your relative is in another state. Otherwise he WILL use the starter to crank the engine while the bolt is in there. Even if he has to hook up the battery to do it.

dka-66 · #12 06-14-2009, 07:09 PM

Quote:

Originally Posted by JonL

I've used the liquid method on rotary engines that have no well-defined TDC (as in a true dead spot where the piston stops and reverses direction). You have to work quickly because there may be a tiny bit of leakage past the rings. There's also air that gets trapped, and the oil sticks to the tubing, and all sorts of things conspire to make you less than 100% certain about accuracy.

The bolt method seems like it would be very accurate and easy, provided the spark plug hole gives a good angle to the piston. Do this method only when your relative is in another state. Otherwise he WILL use the starter to crank the engine while the bolt is in there. Even if he has to hook up the battery to do it.

thanks for the info about making sure to do it quick, I might try to bolt method first and just make sure I am very gentle while turning it.

As far as the brother in law not being in state, That is a big check! He used my Dremel last year that I have owned for 7 years and taken good care of (like all my tools), the next time I went to use it I opened the case and the wheel he was using was jambed into the Dremel so hard I needed pliers to get it out and then I plug it in and turn it on and it is completely dead. He borrowed an older extremely heavy duty Milwaukee 7 inch grinder, I figured there was nothing he could do to this thing to mess it up (I was wrong) I am right handed (so is he) and the handle that screws into the side was on the wrong side so I go to switch it.... He stripped out the threads, no big deal since it was just a drill, tap, and heli-coil but I had to drive to the hardware store to get the heli-coil and the tool to install them.

We live in a nice neighbor hood and I should not have to lock all my stuff up but that is what I have to do..... I have to make sure that the garage doors are locked and anything of value it put up where he can't find them.

OK, enough venting for now.

Ferdman · #13 06-15-2009, 05:45 AM

dka-66, MB crankshafts should only be turned CW. Disregard the portion of the instructions for finding TDC of Piston 1 that mention turning the crankshaft CCW.