offset key for stretched chain - Page 2 - PeachParts Mercedes-Benz Forum

Stretch · #16 03-15-2014, 07:01 AM

Quote:

Originally Posted by Diesel911

I still do not get part or the 2mm Method.
Since the Dial Indicator was set at Zero I am not getting how this happens: "Dial Gauge has gone back by 2mm (valve lift) to 1mm.

I will likely have to read someoned DIY to understand it.

In the Offset Key Selection Chart it looka like if you did the Camshaft Alignment you could use that to select an Offset Key. However, the camshaft Alignment is not a precision as the 2mm Method.

And, then there is the Chart on the first page of the PDF. It has a New Chain and used chain if I remember with 20,000 miles on it specs. I don't recall the instructions saying which of the 2 to use to selecte the offset Key.

People have suggested that the 20,000 Miles is sort of the expected stretch; sort of a break in stretch that was calculated on at the Factory. So you would think that if you were installing a Offset woodruff Key on an Used Chain you would use the Used Chain you would use the Used Chain specs.

So for Me there is a few unknowns.

The procedure is this

You turn the crank until the cam lobe on the intake valve (2nd one in!) over #1 cylinder is pointing upwards

This means two things

a) the valve is closed
b) you are close to the TDC before the intake stroke

The clearance between the rocker arm and the cap on the valve stem needs to be removed. So you set the valve clearance to zero - if you like no feeler gauge fits.

You now set up your DTI (clock gauge) by putting the probe on the valve spring retainer

You push the DTI downwards so that you have a 3mm pre-load.

You need this pre-load because although this method is called the 2mm "lift" method - the valve will drop downwards into the cylinder {but the valve "lifts" from the valve seat}

If you don't have any pre-load, the needle on the DTI stays in the same position

With the 3mm pre-load set you continue to rotate the crank in its normal direction of rotation until the DTI shows a drop of 2mm - so it will be reading 1mm

This is the point at which you read off the graduations at the crank

############

Please note this is NOT the elongation

############

You now have to find the camshaft code on the back of the camshaft (near to cylinder #5) and compare the measurement you have made with the data in the FSM

Diesel911 · #17 03-15-2014, 11:05 AM

Quote:

Originally Posted by Stretch

The procedure is this

You turn the crank until the cam lobe on the intake valve (2nd one in!) over #1 cylinder is pointing upwards

This means two things

a) the valve is closed
b) you are close to the TDC before the intake stroke

The clearance between the rocker arm and the cap on the valve stem needs to be removed. So you set the valve clearance to zero - if you like no feeler gauge fits.

You now set up your DTI (clock gauge) by putting the probe on the valve spring retainer

You push the DTI downwards so that you have a 3mm pre-load.

You need this pre-load because although this method is called the 2mm "lift" method - the valve will drop downwards into the cylinder {but the valve "lifts" from the valve seat}

If you don't have any pre-load, the needle on the DTI stays in the same position

With the 3mm pre-load set you continue to rotate the crank in its normal direction of rotation until the DTI shows a drop of 2mm - so it will be reading 1mm

This is the point at which you read off the graduations at the crank

############

Please note this is NOT the elongation

############

You now have to find the camshaft code on the back of the camshaft (near to cylinder #5) and compare the measurement you have made with the data in the FSM

What is confusing to Me is that in the Manual after you set the Prelaod of 3mm you are ask to set the Dial Dial Indicator at Zero.
If I start at Zero and I rotate the engiine till the Valve is pushed down 2mm I get a 2mm reading not 1mm.
If you have time would you read the German Instructions you have and see if it is not an error in the Engilish Translation.

Stretch · #18 03-15-2014, 11:46 AM

Quote:

Originally Posted by Diesel911

What is confusing to Me is that in the Manual after you set the Prelaod of 3mm you are ask to set the Dial Dial Indicator at Zero.
...

It is actually saying move the outer part of the DTI - move the scale - so that the number zero on the scale is under the large pointer. The small pointer within the larger part of the gauge is still meant to be pointing at three.

Quote:

Originally Posted by Diesel911

...

If I start at Zero and I rotate the engiine till the Valve is pushed down 2mm I get a 2mm reading not 1mm.
If you have time would you read the German Instructions you have and see if it is not an error in the Engilish Translation.

Most DTIs work in a direction that is opposite to the drop of the valve. So if you push on the probe of the DTI the numbers on the gauge increase. However the valve direction is going down - think of it as valve "drop" for the sense of this direction.

If you start with the DTI set at zero the valve drops down - the probe stays at the same height. The DTI is still at zero because it doesn't measure negative displacement. You need to apply enough pre-load on these DTIs to make sure you have enough distance within the gauge to allow for the 2mm measurement. Because as far as the gauge is concerned you have to measure backwards.

You could in principle pre-load your DTI to 10mm and then drop the measurement on the little needle within the large scale to 8mm

You could start at 6.5 and drop down to 4.5 on the little scale

etc etc etc

Each time you do this however it helps to "zero" the big needle so that you can easily see each whole mm change.

Sorry to go on!

Another way of thinking about it => The big needle sweeps round twice for a 2mm change in distance at the probe. The little needle within the gauge just moves a bit...

Diesel911 · #19 03-15-2014, 05:22 PM

Quote:

Originally Posted by Stretch

It is actually saying move the outer part of the DTI - move the scale - so that the number zero on the scale is under the large pointer. The small pointer within the larger part of the gauge is still meant to be pointing at three.

Most DTIs work in a direction that is opposite to the drop of the valve. So if you push on the probe of the DTI the numbers on the gauge increase. However the valve direction is going down - think of it as valve "drop" for the sense of this direction.

If you start with the DTI set at zero the valve drops down - the probe stays at the same height. The DTI is still at zero because it doesn't measure negative displacement. You need to apply enough pre-load on these DTIs to make sure you have enough distance within the gauge to allow for the 2mm measurement. Because as far as the gauge is concerned you have to measure backwards.

You could in principle pre-load your DTI to 10mm and then drop the measurement on the little needle within the large scale to 8mm

You could start at 6.5 and drop down to 4.5 on the little scale

etc etc etc

Each time you do this however it helps to "zero" the big needle so that you can easily see each whole mm change.

Sorry to go on!

Another way of thinking about it => The big needle sweeps round twice for a 2mm change in distance at the probe. The little needle within the gauge just moves a bit...

That explains it.
I am used to only looking at the big Pointer and counting the revolutions or where the big Pointer moves to.

I generally don't pay attention to the smaller dial and pointer because the amount I normally measure is in thousands of an inch (not used to the Metric stuff) so I am not used to the Large Pointer Moving much.

The Dial Indicators I have for this sort of thing have a minimum of 1 inch or more of plunger travel.

If I did this job I would normally have the Plunger pushed up into the Indicator/preloaded randomly just slightly past 3mm of preload (I would watch the large Pointer to see I got 3mm+ of preload movement) and I would zero the Indicator and watch the Large Pointer movement as the Valve goes down till I saw the large Pointer reached 2mm of movement.

One of the Dial Indicators I have has a 1/4" (6.35mm) total plunger range and it does not have the smaller Dial on it; see the pic.
I can do the Job with that dial Indicator but I cannot follow the Instructions with it because there is no smaller dial on it.

Stretch · #20 03-16-2014, 02:15 AM

Quote:

Originally Posted by Diesel911

...I can do the Job with that dial Indicator but I cannot follow the Instructions with it because there is no smaller dial on it.

All you have to do is find a way of measuring the 2mm of travel on that valve

As I mentioned in post #4

Quote:

Originally Posted by Stretch

...

A well respected member suggested that if no clock gauge is available you can lean your chin on say the front of the engine or the front of the engine bay and estimate the drop of the valve spring by placing a ruler behind. This of course is not as accurate as a clock gauge but because the off set keys only come in set sizes the error in your measurement is likely to be within the sizes that are available.

...

I hope this helps

Diesel911 · #21 03-16-2014, 01:05 PM

Quote:

Originally Posted by Stretch

All you have to do is find a way of measuring the 2mm of travel on that valve

As I mentioned in post #4

I hope this helps

Thanks to your explination I undersand it.

But, I tried to explain why I did not undersand the Instructions in the Manual. Mercedes assumes you are using the same Special Tool Dial Indicator in their Tool List. And, the instrctions are for that particular Dial Indicatorn.
If you have a Dial Indicator that lacks the 2nd small Dial the Instructions are confusing because you cannot follow them with that type of Indicator.