#1 cam lobe position - PeachParts Mercedes-Benz Forum

jarbojack · #1 03-29-2011, 10:38 AM

I have a dump question...what do the cam lobes look like atdc on cylinder #1 and at the beginning of compression stroke for #1 cylinder. A photo would be great or an explaination or both.
Many thanks
Jack

SD Blue · #2 03-29-2011, 11:08 AM

What year/model is your car? The later models don't require valve adjustment. (Edit User CP on blue header bar above.)

Here is information from the DIY section of the forum:http://www.peachparts.com/shopforum/showthread.php?t=107729

vstech · #3 03-29-2011, 11:16 AM

ATDC the lobes should have just closed the intake, and the exhaust should be on it's way to the valve.
looking at the front of the motor on a 617/616 the closest lobe to you should be pointing almost straight up I'd think, and the intake should be about the 9oclock position.

Stretch · #4 03-29-2011, 02:12 PM

Quote:

Originally Posted by vstech

ATDC the lobes should have just closed the intake, and the exhaust should be on it's way to the valve.
looking at the front of the motor on a 617/616 the closest lobe to you should be pointing almost straight up I'd think, and the intake should be about the 9oclock position.

This is right for the intake valve if you have the crank at TDC and the mark on the first camshaft tower aligned with the one on the ring that fits onto the front of the camshaft...

...If you were doing the 2mm lift method you'd have to turn the crank again for almost a complete revolution (so about half a revolution on the camshaft) to put the cam lobe above the intake valve at about 3 or 4 o'clock to get the desired crankshaft position to measure your timing chain elongation.

So don't forget that for one complete revolution of the camshaft, the crankshaft rotates twice in a four stroke engine. (Alternatively one rev of the crankshaft gives half a rev of a camshaft)

leathermang · #5 03-29-2011, 04:44 PM

Quote:

Originally Posted by jarbojack

I have a dump question...what do the cam lobes look like atdc on cylinder #1 and at the beginning of compression stroke for #1 cylinder. A photo would be great or an explaination or both.
Many thanks
Jack

There is a lot of squishyness in this thread...

what is atdc ?

Did you mean At TDC ?

I do not know of an ' atdc '... unless you mean ' after top dead center'.. which is a less than exact place.

leathermang · #6 03-29-2011, 04:50 PM

Quote:

Originally Posted by Army

This is right for the intake valve if you have the crank at TDC and the mark on the first camshaft tower aligned with the one on the ring that fits onto the front of the camshaft...

...If you were doing the 2mm lift method you'd have to turn the crank again for almost a complete revolution (so about half a revolution on the camshaft) to put the intake valve at about 3 or 4 o'clock to get the desired crankshaft position to measure your timing chain elongation.

More squishness... the OP did not say what he wanted to find this thing for..
if for chain elongation purposes.. then the use of the cam mark is specifically forbidden by the FSM.. because it is simply not accurate enough to be of service.

Army, could you rewrite the part about the 2mm lift method..
' put the intake valve at about 3 or 4 o'clock' will make no sense to you when you reread it... I know you are talking about the cam lobe..
BUT the deciding factor is the movement of the valve... so ' eyeballing ' the position of the cam lobe is less than useful in understanding the process.. which we actually have not determined from the OP... as far as I can figure...
and it should be the ' movement' of the number one valve.... since it is not being lifted.. but in fact pushed downwards... unless the engine is upside down...

jarbojack · #7 03-29-2011, 05:52 PM

Thanks Leathermang
I was just following up on a reply that you made on a previous post of mine...

"Ok.. so in setting the cam position...
you did not check it by using the movement of the number one intake valve of the number one cylinder ?
You used the Cam mark... which is described in the FSM as only for setting the engine when it is being built ?
And without the drip tube in your possession you have not set the timing with reference to the movement of the number one valve....
So basically you are not sure ( since you were not using FSM procedure) that your fuel is being inserted at some trustworthy relationship to the crank or the cam lobes (?).....

I think you need to back up to as basic as you are able...and see that all things are to specs coming up from there..."

I was going back to basics and rechecking my steps. I used the cam mark to check my at top dead center (sorry my fault for trying to use acronyms to which you correctly stated that the FSM warns against. I am trying to confirm that I have the cam lobes positioned correctly so that I can time the injection pump.
Jack

leathermang · #8 03-29-2011, 06:48 PM

Jack, have you found the excellent descriptions in the archives about how to determine if the engine is in the correct place for timing the injection pump ? Long detailed threads by people who have done it correctly many times... I only needed to do it once and TCane was here to show me and TxBill how to do it.... otherwise I am relating what the FSM says about these things... particularly the WARNINGS..which are often absent in forum discussions.. but which are all over the pages in the FSM...

Stretch · #9 03-30-2011, 03:25 AM

Quote:

Originally Posted by leathermang

More squishness... the OP did not say what he wanted to find this thing for..
if for chain elongation purposes.. then the use of the cam mark is specifically forbidden by the FSM.. because it is simply not accurate enough to be of service.

Army, could you rewrite the part about the 2mm lift method..
' put the intake valve at about 3 or 4 o'clock' will make no sense to you when you reread it... I know you are talking about the cam lobe..
BUT the deciding factor is the movement of the valve... so ' eyeballing ' the position of the cam lobe is less than useful in understanding the process.. which we actually have not determined from the OP... as far as I can figure...
and it should be the ' movement' of the number one valve.... since it is not being lifted.. but in fact pushed downwards... unless the engine is upside down...

I'm sorry to upset you Greg - I've edited my post and put it in bold for you. Can I get off of the naughty stool now?

I was trying to point out that you could position the crank at TDC but the camshaft could be in one of two positions - I used a rough description of the 2mm lift method to demonstrate my point and to put the position of the cam lobe in the context that John started (i.e. 3 o'clock etc)