Valve Timing - Entry into Service Guide

[Jim]

Am I correct in thinking the headings in this picture taken from Section 5 of the Introduction into Service (Model year 1992 (USA) are wrong?

The column headings on the right should read

Inlet Opens Before TDC
Inlet Closes After BDC
Exhaust Opens Before BDC
Exhaust Closes After TDC

 

[gsxr]

No, the headings are correct. They are the same in the FSM. And I've measured the timing on my engine with a dial gauge, everything matched the factory docs.

 

[Jim]

Thanks Dave..

I did some comparisons and the results are attached.



Later...I need to confess that the table I posted does not use consistent valve lift figures; e.g. MB seem to use 2mm while others use something else. This make the cam angle possibly vary by tens of degrees.

On the Lunati Site

http://www.lunatipower.com/Tech/Cams/CamSpecTerms.aspx

I read the SAE standard is 0.006" off of its seat.

Duration measurements are commonly quoted @.050" lift.

Sorry guys.

 

[500AMM]

Am I correct in thinking the headings in this picture taken from Section 5 of the Introduction into Service (Model year 1992 (USA) are wrong?

The column headings on the right should read

Inlet Opens Before TDC
Inlet Closes After BDC
Exhaust Opens Before BDC
Exhaust Closes After TDC

Hi Jim.

Your interpretetion above is wrong - you must think underpressure versus overpressure with regard to the function of each camshaft. The inlet cam cannot open before TDC, it needs to build a certain vacuum to accellerate the inlet airflow into the cylinder when the valve opens. The same with the exhaust cam cannot close after TDC, if so it will such some air into the cylinder.

The table in your last post was interesting, that gives a good picture of the cam lifts, where shorter duration means higher lifts. Compare the 5.0 M119 with the 55 AMG engines, they have quite different camshaft charateristics.

Great info, thanks for posting!

 

[jouniu]

Of course inlet cam opes before TDC, outgoing exhaust gas suck fresh charge inside, and in optimum system all way to exhaust channel, and when piston starts to go down it sucks charge back to cylinder, and then exhaust valve closes.

 

[gsxr]

The intake valve opens AFTER top dead center. Not before.

Remember these values are at 2mm valve lift!!! The factory specs are correct. See what I already stated in my previous post. I've measured the cam timing via dial gauge and the specs match at ATDC, not BTDC. Same with the exhaust cams, btw.

 

[jouniu]

The intake valve opens AFTER top dead center. Not before.

Remember these values are at 2mm valve lift!!! The factory specs are correct. See what I already stated in my previous post. I've measured the cam timing via dial gauge and the specs match at ATDC, not BTDC. Same with the exhaust cams, btw.

Yes 2mm is after TDC, but common cam spec valve opening is measured @0.3mm and in normal 4-stroke engine that happens before TDC.

 

[gsxr]

At 0mm or 0.3mm the MB intake cams may indeed be opening before TDC.

At the risk of repeating myself, the MB specs are correct, and at 2.0mm lift, they open AFTER TDC... just like it says in the FSM.

There are other errors in the FSM, but this isn't one of them.

 

[036/199]

At 0mm or 0.3mm the MB intake cams may indeed be opening before TDC.

They do,however very slightly.
Otherwise there would be no sense in overlap to use the speed of the exhaust gas to draw more mixture into the combustion chamber.

A crude explanation,but good enough for that case:

http://en.wikipedia.org/wiki/Valve_timing

The only difference is with this engine that the cam timing is measure with more lift,hence the after TDC spec.
I assume MB did give that spec to make measuring the timing easier.

I do not think that on a stock engine anything noticeable is gained changing the static timing.
Would need cams,modified heads,proper exhaust and intake system to advantage of timing changes.



It would be way more interesting to have a real variable dynamic valve timing on the intake cam instead of the two position system and play with the static timing.
Something that might be even possible with re-designing the existing system by variations of the strength of magnetic field.
Would require a stand alone ECU,though.

Then while at it,it would be possible to add with some machining and fabricating involved the intake camshaft system to the exhaust cam.
Need to run a stand alone ECU anyway,so replacing the ignition system with a coil on spark system is easy anyway.

And there you have a proper variable intake and exhaust cam timing M119 with individual coils.

Duck and out...