I agree with Bonehead. Replace the chain before it wears out, especially if you plan on keeping the car for a long time.

An engine will probably only need one or two timing chain replacements during its life. So, what's the benefit in wringing every last mile out of the original chain? It's going to be replaced eventually. Why not do it at, say, 200,000 miles? That way you get peace of mind and maybe your engine runs better because the chain will stay within spec for many miles to come. The only thing you have lost by doing it early is the interest you would have made on that $100 or so that it cost to get the timing chain.

Those of you who want to rush to replace that timing chain so you can feel better, you might want to check the following thread first:
http://www.peachparts.com/shopforum/showthread.php?t=96572

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

While I can't say for sure, I feel pretty confident that my chain was not replaced and was original equipment. The above linked thread refers to chains breaking due to other factors, including aftermarket chains or poor installation and poor oil change history. We also know that chains break because the tensioners and slides wear out and fail. I can't understand why it isn't worth the piece of mind to inspect your sprockets and replace the chain, tensioner and slides at 200k miles or so (and then at 400k). The fact is my chain broke at highway speed and the conventional wisdom on the board is my engine is not worth saving (maybe this is the same paranoia as chain replacement). Regardless it will cost me at least as much to replace some valves, have the head done, replace head gasket and also replace all of the timing chain components. Maybe its wishful thinking but I think I could have saved myself some money if I had replaced the chain before it broke, a fairly unpredictable occurance within a 5 year, 50000 mile confidence interval.

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Rich Mason
Chapel Hill, NC
1990 300D 285k miles
1993 VW Cabriolet converted to 1.6 TD
1985 VW Westfalia 1.6 TD

Having just purchased a new chain and a used peening tool, I am having a hard time being objective about this issue. I must say, the thread linked by DieselAddict is persuasive. I am especially concerned about the failures caused by improper installation, which is why I bought the fancy peening tool.

The problem I have with Beagle's recommendations is that I don't have the equipment or skill to do the measurements described in his post. I also don't know a mechanic who I would trust to do it.

Part of me is tempted to check the elongation using the dial indicator method described in the FSM and then replace the chain when I see some elongation. My reservation with doing it that way is that I don't have a baseline measurement. I would have to assume that the motor started out right at spec.

Why can't life be simple?

I look at it as the same as paying $25 for an oil analysis that tells you you can extend your oild change 1,500 miles....its easier and cheaper to do the frequent schedulaed changes.

Same with TIming chain....you might go through 2 maybe 3 of these in the life of the motor...finding out when its going to be time is going to cost you almost as much as a preemptive replacement...if you pay to have it checked just a couple times..................another case of being penny wise and pound foolish....

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I'm doing the chain in my 603 this summer, it should have about 250k on it. It is due and only costs about $125 money well spent in my book. Besides my mileage is off a bit and I want to ring every mile out of the $2.50 diesel fuel.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

One item that Beagle mentioned that most people don't talk about or do... putting new sprockets on to match the new chain....
This is a LOT more work than rolling in a new chain....due to the position of the lowest sprocket...
But it is the 'proper' way to do it.

he says it here:
A chain worn in excess of 6º should be replaced not because it is in imminent danger of breaking, it isn’t, but because the difference between the pitch of the chain and the pitch of the sprocket teeth is now excessive. Instead of the load being spread evenly between all the engaged sprocket teeth (25 at the cam.) the entire load is now on the leading 2 or 3 teeth causing sprocket and chain wear to increase rapidly and exponentially.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

I think some of you are still missing the point. From the other thread it's apparent to me that the chain is one of the strongest parts of the car. If it's not significantly stretched I see absolutely no point in "rolling in a new chain". If something is going to fail, it's more likely going to be the vacuum pump that will throw its bearings into the timing chain cavity, or it might be one of the timing chain guides that fails (less likely), both of which can rip the chain regardless of whether it's new or old.

Leathermang, I don't think Beagle meant to put in a new sprocket as part of regular maintenance when a new chain is being installed. He meant to replace it only if it has visible damage.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Hatterasguy:
After changing the timing chains on both of my MB's, the fuel economy improved by less than 1 mpg on the 81 SD, and over 3 mpg on the 78 300D. The 300D also lost its nagging idle miss.
The 81 was showing somewhere near 3 deg of stretch, the 78 was showing over 7 deg.
Since the 78 had very high miles when I changed the timing chain, I would guess that it was stretched over the limit to run properly. Three mpg improvement is significant. So was losing that idle miss.

A good place to start is to measure the timing chain stretch the simple and less accurate way. Line up the TDC marks on the cam and read the number of degrees off the crank. It is generally accepted that this will tell you whether the stretch is something to worry about, it will not however tell you the precise amount of stretch. This is what I did and I got 2-3 degrees. I'm not worried.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

" I don't think Beagle meant to put in a new sprocket as part of regular maintenance when a new chain is being installed. He meant to replace it only if it has visible damage."

He was referring obliquely to it when he told about a certain amount of stretch in a chain causing the load to be on very few of the sprocket teeth...
And of course many of us do not know if others have already rolled in new chains in the past... meaning the wear on the sprocket will tend to accelerate the wear on the new chain being put in...
The top sprocket would be easy to change out... on the camshaft end... and would be better than nothing with regards to longivity.

I didn't realize how much was already written and explored on this subject. It seems that if Beagle is right about a worn chain accelerating the wear on the sprockets, it would be prudent to replace a chain on a 617 at 5 degrees. That could preserve the sprockets, assuming they are ok to start. Whether or not the chain can be used to the full extent of the offset keys should be irrelevant.

Another thought I had on using offset keys...once you retime the cam with one, you lose your original reference to chain wear. If you forget, or sell the vehicle, you may check cam timing in the future and mistakenly assume the chain is not extensively worn, when it could get beyond spec.

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'83 240D with 617.952 and 2.88
'01 VW Beetle TDI
'05 Jeep Liberty CRD
'89 Toyota 4x4, needs 2L-T
'78 280Z with L28ET - 12.86@110
Oil Burner Kartel #35

http://i16.photobucket.com/albums/b1...oD/bioclip.jpg

Anyone who has ever ridden a dirt bike knows about sprocket wear.....

if you trie to get that last mile out of the chain your sprockkets are gonna pay for it.

But sprockets on a bike are far easier to replace.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Old300d,
You have missed an overall concept in this chain stretch checking equation.
The factory shop manual gives you a ' performance objective' to meet which has to do with Valve Timing. A 2 mm movement of the intake valve of the number one cylinder.
The relationship between the valve timing and the crank position is important... the point in the cycle at which the injection pump gives the engine fuel is important... but can be set independantly.
The relationship between the cam sprocket position and the sprocket on the crank are determined by the wear on the slide rail on the drivers side of the engine and the number of links in the chain and the amount of wear on each pin and link added together.
The Mercedes people gave you four offset keys to change the cam position relative to the cam in order for you to get within running specs... until you run out of bigger offset keys.. at which point the factory specifies that you need a new chain installed.
Putting a new chain on a worn sprocket will also accelerate wear.. because the old ones have been ' worn in to match each other' .....
Only great solution is new chain and sprockets...

BoneheadedDoctor, from one old dirt biker to another... AMEN....