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  #1  
Old 12-23-2002, 07:41 AM
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300k and no T/C Stretch ??

Is this normal? Finally got to the 150k valve adjustment on Saturday and now it starts beautifully when cold once more..did a double take and checked it twice but with 290k on the odometer, the timing is right on the mark. Its the original chain..am I just plain lucky or do they actually last this long? Based on all of the related posts, I had expected to have to replace it.

On another note, the vaccuum switch gizmo on the top of the valve cover..what does it do? The two piston pins on the actual valve/switch..it looks like the little plastic "flappers" used to extend under the pins when new and acted as part of the actuator. These look like they just plain wore off (there's just thin little plastic stubs left) so now the pins just ride on the plastic cam (which is starting to develop grooves). If so, it means the pins don't get pushed up as far. Is my hunch correct and would such wear affect anything?

Thanks and Happy Holidays..

MikeL

84 300 CDT

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  #2  
Old 12-23-2002, 08:35 AM
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Would you describe the procedure you went through to check the chain stretch ?
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  #3  
Old 12-23-2002, 12:39 PM
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MIkeL,

To to be negative, but I find it unlikely that you have zero stretch. Even later models (601,602,603,606) engines which tend to show lower TC wear, still have 3-4 degrees.

It's more likely that it has had a chain put on the car. Of course, someone could have used offset keys on the camshaft to offset the wear. Are there witness marks on the IP bolts??


Michael
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  #4  
Old 12-23-2002, 12:43 PM
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Your vacuum questions=)

First, if you have not much damage on the cam, replace those plastic thingys. I've heard you can get them instead of the whole valves for $1 or so.
I believe they help fake a vacuum curve for the transmission modulator.
oh, I don't think you are suppose to use grease on those parts. Dry. Keep the linkages lubed.


Michael
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  #5  
Old 12-23-2002, 01:08 PM
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Samiam4, my post was another way of saying that.. perhaps the method of checking the stretch is what caused this impression...
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  #6  
Old 12-23-2002, 02:02 PM
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timing chain check

Rotate clockwise and the notch on the camshaft washer lines up with the mark on the tower..the pulley/damper crank line mark at 0 (just to the left of the pin when looking down) lines up with the pointer.
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  #7  
Old 12-23-2002, 03:16 PM
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So you did not use the position of a valve , like 2 mm travel from rest, after you had decreased the valve to cam distance to zero ?
I am not for SURE on your car.... but I suspect you are not using the proper method for checking stretch, thus got the impression you have none even at 300k..
Someone will post telling the proper way....I hope...

Last edited by leathermang; 12-23-2002 at 03:59 PM.
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  #8  
Old 12-23-2002, 05:04 PM
LarryBible
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Leathermang is indeed describing the correct timing chain test method, and if you want to be sure, you should follow his instructions. However, if you are turning the harmonic balancer slowly and stop exactly when the cam and cam stand marks line up, then you check the harmonic balancer mark and it is right on, you are probably okay.

It is entirely possible that your chain has no stretch at this mileage if you have been religious about FREQUENT oil and filter changes.

My 240D was very close to zero stretch at 380,000 miles, so I know that it is possible.

Merry Christmas,
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  #9  
Old 12-23-2002, 05:07 PM
turbodiesel
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My car had religous oil and filter changes every 3000 to 5000 miles, yet it had over 13 degrees of stretch at 272,000 miles.
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  #10  
Old 12-23-2002, 05:20 PM
LarryBible
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My response was not very thorough. The point I'm trying to make is that it is POSSIBLE to have minimal timing stretch with VERY FREQUENT oil change intervals. In this case, frequent would be a MAXIMUM of 3,000 for highway driven cars, and less if driven short hops. Anything further than that could allow excessive microscopic particulate matter to take its toll.

Additionally, draining the oil while hot, and draining for an extended period goes a long way toward getting the last drops of nasty sludge from the bottom. Those last nasty drops that come out are the nastiest, sludgiest, particulate filled portions of all the oil that comes out.

This is why I believe in hot, overnight drains.

Merry Christmas,
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  #11  
Old 12-25-2002, 05:59 AM
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Larry, ...Naw, I don't believe it. I know you know what you are talking about in ALL things ...but, no stretch in that many miles? Naw, I don't believe it. Someone snuck into your garage when you were away and put a chain on. Had to be. :p
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1988 Cadillac Eldorado (better car than you might think!)
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1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
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"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"
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  #12  
Old 12-25-2002, 08:33 AM
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I think it would be interesting to do the math on the number of times that chain would travel through the cycle in that many miles ......
I did the math on my Volkswagon just going on one five hour drive from Dallas to Houston.... and it was about 2,000,000 revolutions.... yes two Million....
So I think that going 300k without a reasonable amount of wear would be very hard...
How many turns of the crank does it take for one cycle of the chain ? I may have phrased that wrong to help visualize it .. but it is early in the morning...
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  #13  
Old 12-25-2002, 04:49 PM
XN6guy
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Quote:
Originally posted by 240 Ed
...but, no stretch in that many miles?

Actually he said "very close to zero stretch", which implies a few degrees. I think this is believeable.
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  #14  
Old 12-26-2002, 09:21 AM
LarryBible
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Whether one chooses to believe what I say is their business. Many people on this forum have questioned and even ridiculed my obsession with frequent, hot, overnight oil drains with a fresh filter every time.

Couple my oil change fanaticism with the fact that the 240D very rarely ran 20 miles or less after startup, with 90 miles after startup being the more typical minimum, and you have the ideal situation for maximum engine life.

How many people drive their cars 100 miles minimum almost every time the engine is started. This makes for very few cold starts per mile driven as well as minimal engine oil contamination. Add to that the use of Universal grade oil that is designed to deal with soot dispersal.

All this adds up to the absolute minimum particulate matter circulation in the oil, leading to maximum chain life.

Again, if one wishes to imply that I am a liar, that is their own business.

Happy New Year,
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  #15  
Old 12-26-2002, 09:51 AM
XN6guy
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Speaking of chain stretch... How exactly does clean oil affect timing chain stretch? It would seem to me that oil cleanliness would be a secondary issue in that particular department.

It seems like the density and tempering of the chain's steel would be the primary consideration. Has anyway formulated a theory on this, or is there an official explanation somewhere?

It seems to me that the few cases of minimal stretch are probably due to fluctuating manufacturing tolerances at Mercedes-Benz... some chains are made from a better chunk of steel OR they are tempered better.

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