The proper way to measure chain stretch

[dannym]

There are two ways to determine chain stretch. The first method is commonly called the 2mm valve lift method. This is the method that Mercedes Benz specifies. It will give you a highly accurate reading.
The second method consists of aligning marks on the front cam bearing tower and the sprocket thrust washer. This method can give you an accurate reading but it all depends on how accurate the marks are aligned.
It's not necessary to bring out the dial indicator every time you have the valve cover off. Aligning the cam marks is a good way to see where the chain is at.
I like to check with the dial indicator once maybe twice a year to get an accurate reading.
Ok lets get started.

1-The first thing to do is remove valve cover. It will help putting things back together if you take pictures.



2-Setup intake valve #1 pointing up in relation to rocker arm. Intake #1 is the second valve from the front.



3-Just remove valve lash.



4-Remove magnetic base from dial indicator post holder and install as shown. Use channel locks to gently make sure it's tight.



5-Setup your dial indicator. It will take some finagling but it will work.

[dannym]

6-Dial indicator post should be on the valve keeper. Make it as straight up and down as you can. This dial has a 1" travel. If you are going to purchase a dial indicator buy one with a 2" or more travel. This will allow you to get it straight vertical.



7-Note that the cam lobe has moved 90 degrees and there is no movement on the dial indicator.



8-Crank engine at crankshaft until dial indicator shows 2mm lift. 2mm = 0.080 inches. No it's not reading 0.020 inches it spun around counter clockwise.



9-Read degrees at balancer. This reading is 11 degrees.



That is not our chain stretch. to determine chain stretch we have to go to the Factory Shop Manual and get specifications.

For engine(s) 615.912/913, 615.940 (40kw), 615.941, 616.916, 616.912 (48kw); Camshaft code(s) 02 & 06, specs are:
With new chain 11.5 degrees ATDC.
With used chain (from approx. 20,000 Km) 13.5 degrees ATDC.

For Engine(s) 615.940 (44kw), 616.912 (53kw); Camshaft code 10, specs are:
With new chain 9 degrees ATDC.
With used chain (from approx. 20,000 Km) 11 degrees ATDC.

For engines 617.910, 617.912 (59kw); Camshaft code(s) 00 & 08, specs are:
With new chain 11.5 degrees ATDC.
With used chain (from approx. 20,000 Km) 13.5 degrees ATDC.

For engines 617.950 (up to year 1979); Camshaft codes 00 & 08, specs are:
With new chain, 11.5 degrees ATDC.
With used chain (from approx. 20,000 Km), 13.5 degrees ATDC.

For engines 617.950 (1980 and after), 617.951, 617.952; Camshaft code 05, specs are:
With new chain, 9 degrees ATDC.
With used chain (from approx. 20,000 Km), 11 degrees ATDC.

Verify engine number by reading the stamp on the engine block. It is located under glow plug #5 near the oil filter.

Note: Cam codes are stamped on the rear of the cam.

You take your reading off the balancer, compare it to the proper specifications for your engine. The difference is the actual chain stretch.

Mercedes Benz makes 4 woodruff keys for the correction of cam timing:
Part # 621 991 04 67, Offset 0.7 mm, For correction of about 4 degrees.
Part # 621 991 02 67, Offset 0.9 mm, For correction of about 6.5 degrees.
Part # 621 991 01 67, Offset 1.1 mm, For correction of about 8 degrees.
Part # 621 991 00 67, Offset 1.3 mm, For correction of about 10 degrees.
Choose and install appropriate key.

For this engine, 617.951 the chain is right on at 11 degrees. I installed a 4 degree woodruff key on June 11, 2005. Almost 8 months later the chain is still in great shape.

[rg2098]

You photos are a bit small to see. Can you up the size? This can be put into the DIY forum.

[dannym]

10-Trying again with cam timing marks.
Align the marks as shown. They have to be PERFECTLY centered! Even a little off will throw off your reading.



Read chain stretch at balancer. Looking at the specifications we see that Mercedes Benz builds their chains to wear in 2 degrees at roughly 20,000 Km. Using this method you should see 2 degrees at the balancer. What we see her is an accurate reading.



11- Reset valve lash back to spec then put it all back together.



Checking and correcting chain stretch is an integral part of maintaining your engine. However you also want to make sure your tensioner, guides and rails are in good shape. Failure of any of these parts can lead to catastrophic failure of your chain and engine.

Also don't leave your ratchet on the crank bolt.

[TheDon]

Originally Posted by dannym

Hold on this is a work in progress I'm not done yet

That's the limit for attachments. I'll host hem later and repost them for now I want to finish up this way.

www.photobucket.com

[jbaj007]

Nice.

Might edit #8) 2mm. = .80" (should be .08" )

Edited: .08" done.

[Brian Carlton]

An excellent writeup and fantastic photos..........however.............

There is a problem with the execution of both procedures.

The spec for a used timing chain is 11° ATDC using the dial indicator. You have 7° ATDC. This means the timing is 4° early. Possible, but highly unlikely.

Furthermore, you have a reading of 10° ATDC when you align the marks on the tower. With a brand new chain, this reading would be 0°.

So, you deviate from your readings taken with the dial indicator by 14°. It's inconceivable that the engine is 10° late when the mark on the tower is utilized.

We'd like to put this in the DIY forum........but.........the aforementioned discrepancies need resolution.

[dannym]

Originally Posted by Brian Carlton

An excellent writeup and fantastic photos..........however.............

There is a problem with the execution of both procedures.

The spec for a used timing chain is 11° ATDC using the dial indicator. You have 7° ATDC. This means the timing is 4° early. Possible, but highly unlikely.

Furthermore, you have a reading of 10° ATDC when you align the marks on the tower. With a brand new chain, this reading would be 0°.

So, you deviate from your readings taken with the dial indicator by 14°. It's inconceivable that the engine is 10° late when the mark on the tower is utilized.

Hmmm...you make a good point. Now I wish I still had that picture of the timing mark with the cam marks aligned.

Too bad it's dark out. I'm goint to have to put this on hold for a while until I have time to investigate. The problem I have is my cam code is not listed but 11 degrees should be good specs for vehicles later than 1980.
I'll get back to this when I can.

Danny

[whunter]

When it is edited for content, Please send the completed DIY to Bill = webmaster@peachparts.com
with a note giving explicit written permission to add it to the DIY wickka page.

This has great photos + data, and needs the protection that adding to the DIY Wikka page will give.

Thank you.

[dannym]

Ok I got it right I think.

I believe the post moved on the dial indicator when I was turning the crank. Which only gave me a reading of 7 degrees at the crank. I made sure everything was real tight and it worked right.
As far as the cam timing marks I think I mixed up the 0/0 with the 1/0 mark.

Anyway the tutorial is complete. I will leave it open for remarks and comments before I submit it to Bill.

Danny

[Brian Carlton]

Originally Posted by dannym

Ok I got it right I think.

I believe the post moved on the dial indicator when I was turning the crank. Which only gave me a reading of 7 degrees at the crank. I made sure everything was real tight and it worked right.
As far as the cam timing marks I think I mixed up the 0/0 with the 1/0 mark.

Anyway the tutorial is complete. I will leave it open for remarks and comments before I submit it to Bill.

Danny

Excellent job.

My only concern is the rather large error when the marks on the tower are utilized. In your specific case, the deviation was approx. 6° when compared to the measurement obtained from the valve lift. While the method using the marks is not perfect, it should normally be closer than 6°. As a comparison, the SD shows a reading of 2.5° on the crank damper when the marks on the tower are utilized. I cannot believe that an engine with 180K would have no stretch in its chain, so, the 2.5° reading is probably close to the actual chain stretch.

My feeling is that the marks on the tower are adequate for most users in the forum, especially due to the lack of a dial indicator in most cases. However, the conclusion to be drawn from the procedure above would be quite the opposite. You might consider editing to note that your result may be atypical. Note, however, that we probably don't have sufficient data to judge.

[Pete Burton]

This was so well written I feel compelled to add: http://www.peachparts.com/shopforum/showthread.php?t=96572&highlight=Stuttgart

..explains why the cam and tower marks don't always line up.

[dannym]

Originally Posted by Brian Carlton

Excellent job.

My only concern is the rather large error when the marks on the tower are utilized. In your specific case, the deviation was approx. 6° when compared to the measurement obtained from the valve lift. While the method using the marks is not perfect, it should normally be closer than 6°. As a comparison, the SD shows a reading of 2.5° on the crank damper when the marks on the tower are utilized. I cannot believe that an engine with 180K would have no stretch in its chain, so, the 2.5° reading is probably close to the actual chain stretch.

My feeling is that the marks on the tower are adequate for most users in the forum, especially due to the lack of a dial indicator in most cases. However, the conclusion to be drawn from the procedure above would be quite the opposite. You might consider editing to note that your result may be atypical. Note, however, that we probably don't have sufficient data to judge.

Thanks Brian, I appreciate all your input.

At 6 degrees the mark was actually past on the camshaft. I tried multiple times to get it to line up and I gave up. Lined up perfectly it would have been around 4, no lower than 3, I estimate.
It does have stretch. I mentioned I installed a woodruff key last June.

I agree about the cam marks. I don't break out the dial indicator every time I have the valve cover off. The purpose of the write up was to explain the right way to do it.
I wouldn't pick out a woodruff key using the cam marks as a reference.

Danny

[Brian Carlton]

Originally Posted by dannym

Thanks Brian, I appreciate all your input.

At 6 degrees the mark was actually past on the camshaft. I tried multiple times to get it to line up and I gave up. Lined up perfectly it would have been around 4, no lower than 3, I estimate.
It does have stretch. I mentioned I installed a woodruff key last June.

Since you and I both agree that the degree marking at the crank would probably be about 3 or 4 degrees, if the procedure was done perfectly, my suggestion would be to go and photograph the crank damper with the mark right at 3.5°.

Of course, this is a fabricated result, however, I think we agree that it would be more meaningful for all concerned if the photo did not show 6°.

You currently have a Woodruff key that brings you back to perfect cam timing, as if you had a brand new chain. The procedure using the cam tower should result in 0° on the damper, yet it results in 3.5° or so due to the limitations of using the cam tower. This would be a valid conclusion and you should so state it in the writeup.

[dannym]

Originally Posted by Brian Carlton

Since you and I both agree that the degree marking at the crank would probably be about 3 or 4 degrees, if the procedure was done perfectly, my suggestion would be to go and photograph the crank damper with the mark right at 3.5°.

Of course, this is a fabricated result, however, I think we agree that it would be more meaningful for all concerned if the photo did not show 6°.

You currently have a Woodruff key that brings you back to perfect cam timing, as if you had a brand new chain. The procedure using the cam tower should result in 0° on the damper, yet it results in 3.5° or so due to the limitations of using the cam tower. This would be a valid conclusion and you should so state it in the writeup.

OK i made changes and added a 2.5 degree picture. Not so much fabricated, it was definitely past zero when the marks were almost aligned.

Also, didn't bring it back to brand new specs. I brought it back to used chain specs with the woodruff key.

Danny