Larry, why don't you pick some criteria which you think would come closest to accurate .... and do the math for us... ? Average rpms at the average speed which you drove it.... etc... How many times do you think the chain went past the crank in that number of miles ?

While running the car long enough to heat it most everytime it is started is certainly good for long life... it does not negate the fact that the vast majority of wear happens in the first few seconds of start up, when the metals are not expanded to their designed size and clearances......

And the importance you attribute to hot,overnight oil changes seems to call into question the effectiveness of the oil filters we use...do you have any thoughts on that ?

What oil were you using ? And what was the stretch which you measured at 300k ?

Yes, you are reiterating my point. Because most wear happens during the first few seconds of start up, my engine saw very few cold startups during its life.

As I indicated it was rare when it didn't run less than 89 miles per start up, and many, many times, it ran 300 to 700 miles per start up. If you do the math on this with an average of 150 miles per startup, that means there were only about 20 starts per oil change. Compare that to someone who drives ten miles to the office and changes their oil every 3,000 miles. That means they have 300 cold starts per oil change.

Additionally, the number of cold starts per oil change has another effect, the one I was eluding to in my previous post. That is that the lack of thorough warm up cycles, inhibits the ability to boil out the condensated moisture. This leads to acid build up in the crankcase that causes microscopic corrosion particles to circulate in the oil.

I changed the oil religiously every 3,000 miles, and the engine never saw anything except Delo 400 multigrade. The filters were whatever I found at the foreign auto parts store where I usually buy parts, usually MANN.

Regardless of oil filter, if you run oil very long there is microscopic grit in the oil that the filter will not catch. It is not terribly damaging, but it will gradually shorten engine life.

As far as how many times it turned, I don't know. Even as an anally retentive engineer, I don't give this much thought. If a timing chain or anything else is properly lubricated with CLEAN oil, the number of times it rotates has little to do with wear. It's the RATE of wear that factors into all this. If you have a low rate of wear, then there will be many miles driven, if the rate of wear is accelerated, then you will enjoy fewer miles from that part. To me it's as simple as that.

Oh yes, the amount of stretch. When the engine was relatively young, less than 100,000 miles, I started "checking" chain stretch whenever I had the timing cover off for valve adjustment. I never checked it with a dial indicator, I only turned the harmonic balancer slowly until the cam and stand marks lined up then read the harmonic balancer location. Every time I did this during the life of the engine, the harmonic balancer was always at TDC or a degree or two past. I agree this is not the accurate way to check it, but since I checked it the same way every time, I believe it was a good indication of near zero chain wear.

Happy New Year,

I agree with the cold startup theory. My car was driven about 17,000 miles per year before I owned it and i'm sure it saw 5 cold starts per 100 miles. On average my car sees maybe 1 cold start per 100 miles now.

My dad was a Benz Tech and I always remember him bragging about certain things about Mercedes cars. His favorite motor was the 617 diesel and I remeber him talking about the timing chains and the worst thing for it was to accellerate like a bat out of hell. The Italian tune up, whiule good to clear stuff out on occassion, was the worst thing to do for the chains.
have a great new year,
Adam

Since I first read Larry's recommendation "Change it hot, change it often". I started doing just that. Let it sit overnight and drain.
This has not been my best year with the old beasts, but I can tell you with having taken off the valve covers and working in there, the appearance and 'feel' of the engines have improved to a great extent. Just a lot cleaner. Lots less dirt. Wish I would have thought of that a long time ago. May have saved a few repair$.
So have a Happy New Year Larry Bible, and keep changing it hot!

I have same question as XN6Guy ... while clean oil is obviously important when friction is the major issue, strikes me that issue with timing chain is that is simply stretches as stress and tension occurs over the years ... i.e. no matter how slick the bearing surfaces are or how well lubed the cam or crank sprockets are, that the forces are still at play on the chain .... am having, as you can see, some difficulty in figuring out the physics on this one ...

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

Think about what is actually oiling the chain links. There isn't an oil pump that is forcing lube into the chain. I think the majority of the wear occurs when the oil is cold and thick. It can be squeezed out of the links but is too thick to flow back in effectively. The oil film thickness is probably less than a few microns in the links. When oil is in this situation it is the additives in the oil that help prevent wear. In these tight places clean oil is very important.
The first things that seems to go bad on these cars when exposed to neglect is the timing chain and rings. The main bearing an rods seem to take quite a bit of abuse. The oil film thickness there is large enough to handle more dirt in the oil.

Clean oil is very important! My paper deliver guy changes the oil in his VR Rabbit diesel every 2 months with Delo400. With over 400,000 on it the engine still sounds very good.

I have a centrifugal filter on my 240D and it removes about 3 ounces of dirt in 10000 miles.

stephenson,

I expect that it is the terminology that is confusing you. Most everyone refers to timing chain wear as "stretch." The chain does not really stretch as in the steeling links stretching to become longer. The "stretch" of the chain is due to slight wear in each of the individual rollers and pins. A slight amount of wear in all rollers and pins allows the chain to become longer.

I don't know how many links there are in one of these chains. For the sake of explanation, let's say there are 100 links. If each of the pins and rollers wore .001", that would add up to .100" overall "stretch." This would make the chain almost 1/8" longer when under tension.

Such a slight amount of wear per pin can add up fast. This is why the microscopic particulate in the oil has a dramatic effect with chain wear.

Hope this helps,

I still think for grins that you should choose parameters which you think are close to what your car went through during that 300k miles.... to get a good estimate of the number of times that chain went around those crank and cam sprokets...

What "parameters" are you looking for? All I know is how long it lasted and how I took care of the car.

As far as parameters go, hum the tune and I'll try to pick it up.

I can certainly calculate how many revs the engine made in 380,000 miles if that's what you're looking for, but I see that as a totally pointless calculation.

Happy New Year,

It is my understanding that your engine did not need to be rebuilt at 380k, it just needed a rear seal, right?

Okay, I "get it" now... I interpreted the term "stretch" literally--as in the steel actually stretching, making the chain longer (which would affect valve and injection timing).

A similar thing occurs to Peugeot's old 2.0 liter gas engine. The chain tensioner is hydraulic. When the filter screen on the inlet of the tensioner gets clogged (happens to most of them because of poor maintanence), the chain is no longer tensioned correctly. The teeth on the timing gears now exert a tugging force on the chain--this causes the little rollers to wear abnormally, and it can cause the timing gear teeth to wear into a sharp sawtooth shape.

I respectfully submit to you the actual answer.
The timing chain, while in fact does wear to a small extent at each individual roller, does in fact "stretch" by the fact that the pins wear by elongating the perfect circles they are initially machined into the form of an ellipse, and can be seen in a very simple way.
You can lay a new chain beside an old chain, centering up the initial link and see clearly the elongation of the chain along the length of it. or, you can count links at center-point, and measure between these set number of links between a new and used chain and the difference is stretch.
Also, the stretch would not be magnified as Mr Bible suggested because not every link rides on a sprocket at the same given time. Therefore, only the few links riding on the sprockets would be multiplied to get the sum of the alledged chain stretch.

Thanks, Adam

Adamb, I am not sure what you are saying in the top portion of your last post... but the last paragraph is not correct.... the difference in where the cam should be will be the wear on individual units in the longitudinal construction of the chain... but will be " cumulated"... for the number of links between the crank (power input) and the cam sprockets ( load )....

Larry, I can do the math, but I would have to make some assumptions... I figured you probably knew the rpms you were turning on those 100 mile trips... so you could estimate the number of revolutions your engine made in that time... if I just picked some I could just hear such things as " I had a ______ differential ratio. therefor your numbers are way off.... etc,etc... " So I thought I would suggest you give the parameters... so it would be as close as possible...