Chain stretch method 2mm VS lineup - PeachParts Mercedes-Benz Forum

cho · #1 05-16-2013, 06:44 AM

.

just wondering

has anyone ever done comparison measurement of the chain
stretch using both methods on the same chain.

line up marks VS 2mm method.

most of us do the "ball park" check - line up marks.

I wonder what is the real-world difference in those two.

cheers
ChO

.

Diesel911 · #2 05-16-2013, 12:28 PM

Back in the past there is some Threads and Posts on this.

It has been a long time since I read info on that subject but I believe Brian Carlton spoke about that and maybe Hunter about 4-5 years ago but I don't want to speak for them.

On a 617.
The main problem with the ball park one is lining up the marks accurately. If you stand above the Marks and look down at them and line them up you can be several degrees off due to the Angle you are looking at.
If you use the Marks try to get your Face as close to the marks as you can and look straight on the marks. If needed use a Magnifying Glass.

When I did that I got 2.5 degrees past OT (top dead center). So even with a couple of degrees of error I know nothing bad is going to happen to the Engine from that.
Also the Offset Woodruff Keys don't go that low.

If I had gotten something like 4 or more degrees when I did the ball park test I would be seriously thinking of doing the 2mm Method. And, when you do that you get info that determines what Offset Woodruff key to use; if you want to do that.

Even though I have the Dial Indicator and accessories to do the 2mm Method I have so far not been curious enough to do both checks to see how close they are.

Something that can throw the results of either test off is if there is already an Offset Woodruff Key Installed. The only way to know is to pull the Camshaft Gear fare enough forward to get a clear view of the Woodruff Key. I have had no interest in doing that either.

While People have said the Ball Park test is not accurate when you are rebuilding an Engine the Manual has you useing the same Timing Marks during the rebuild.
So the Marks are sufficient for rebuilding the Engine but not for checking the Timing Chain Stretch or Gear wear/

cho · #3 05-17-2013, 03:37 AM

.

thanks DnineEleven

I examined old posts but no info regarding real world data measured
on the same chain using both methods.

What you described is exactly what I take a line up method for.
During the lining-up my eyes are closest "device" and the head is almost
chin mounted to fuel filter holder

so little or no room at all for error.

but... it will be good to know how much is ball park actually off
given that all is aligned properly. I dont have a 2mm dial or else I would
give it a try.

the question you posted on the end of your previous post
bothers me also..

cheers
ChO

.

Stretch · #4 05-17-2013, 04:12 AM

Here's my take on the situation.

With a new chain and new guide rails and the timing chain tensioner correctly installed the lining up of the 0 degree mark at the crank and the little notch on the cam shaft works every time. It becomes apparent very quickly that one tooth to the left or one tooth to the right is totally wrong!

Note about timing chain tensioners =>

The turbo OM617 has just a spring - it is either good or bad

The non turbo 61X engines have this engine oil filled contraption that needs to be properly primed before it is fitted.

I can imagine that if, for whatever reason, the tensioner is not doing its job properly that strange occurrences in the measurement could be made.

Another possible source of error is that people miss the point they want and they just "back it off a bit" - this could account for a large error in the measurement.

The other point worth making is that if you are aligning the cam shaft mark; any small change in the position at which you stop "at the top" is magnified "at the bottom". One degree of motion at the top is two degrees at the bottom - it is a four stroke engine.

As for the 2mm lift method - I've been told by an honorable reliable forum member (yes there is one!) that you can get a rough idea by resting your chin on a particular part of the engine / radiator and setting a ruler behind the inlet valve. A drop in 2mm is easily seen with the naked eye. Now this isn't as good as using a DTI but it gives you a pretty good idea - especially when you realise that Mercedes only supply off set keys in certain sizes.

Things that can go wrong with the 2mm lift method

1) People measure the wrong valve! It is the second valve from the front you need to measure!
2) People think that the reading at the crank equals the amount of elongation <= wrong! You need to consider your cam shaft type and look up the results in the FSM
3) People fail to align their DTI in a vertical manner - measuring at an angle isn't helpful.
4) People miss their point and just "back it off a bit"
5) People try and do this measurement with the glow plugs still in place! {Actually I've never heard of that one before - I've made it up - could be fun; just imagine!}

Comments about the offset keys =>

You can easily see if one is fitted by removing the bolt that holds the camshaft cog in position. You don't actually need to remove anything else. It is visible behind the washer behind the bolt head. No stress - easy check.

I reckon the offset keys made by Mercedes are little bit out any way see =>

OM617 (non turbo) cam profile specs, piston height specs etc

OM617 (non turbo) cam profile specs, piston height specs etc

cho · #5 05-17-2013, 05:10 AM

Quote:

Originally Posted by Stretch

....any small change in the position at which you stop "at the top" is magnified "at the bottom".

.

well...being a boy I can easily grasp this info ... just hope that my wife
does not call it 2 mm method

just kiddin 'course,great info as always Stretch.. has someone pic
with position of the bolt Stretch talks about (offset keys inspect.) ...red arrow pointer for me noob is also fine

edit: found it

thanks

.

.

Stretch · #6 05-17-2013, 08:03 AM

^^
Nutter!

Here's another link for you

PeachPartsWiki: Measuring Timing Chain Stretch

cho · #7 05-17-2013, 09:07 AM

.

yeah... that's the one that introduced me to all this chain wear mess

.

Diesel911 · #8 05-17-2013, 10:22 AM

It is possible to do the 2mm Method wrong.
You are required to use the Valve Adjusting Nuts to remove the Valve clearence. It is possible for someone to over do that and depress the Valve a little. To prevent that you should have the Dial Indicator already set up on the Valve Spring Retainer so you can see if it moves while you are removing the clearence.

The other probem is if you don't have an extension to screw into the Dial Indicator to make it longer some Indicators will end up and an angle. I the Dial Indictor needs to be straight up and down to be accurate.

I was wishing Brian or Hunter would chime in. What remember being said is that the Ball Park is extremely close to the 2mm Method. I think it is close enough to tell if you need to do the 2mm Method or not

MY Question on Timing Chain Failure
Who has or knows someone that has experienced a timing chain breakage/failure? - PeachParts Mercedes ShopForum

My question What in particular causes vacuum pump failure?
What in particular causes vacuum pump failure?

cho · #9 05-20-2013, 03:34 AM

Quote:

Originally Posted by Diesel911

I think it is close enough to tell if you need to do the 2mm Method or not

I also think that this is safe and proper conclusion considering the
differences between 2 tests.

Thanks D911.

...but,if anyone in the future gonna have means and opportunity to
compare the 2 on same chain please post results.

thanks guys

cheers
ChO

.

vstech · #10 05-20-2013, 08:17 AM

I'll try to get both done on an engine soon... I've got several needing valve adjustment, and several on stands needing work... I'll take plenty of pics as well.
not soon mind you, but I will get to it in my free time...