Could anyone please kindly look up some information for me?

I'm trying to accurately check the timing chain stretch because the car has 204,000 miles on it & I don't know if the previous owner (the proverbial little old lady from Pasadena) ever had the chain replaced. When I measured using the crude method of looking at the alignment marks, it lines up perfectly. It just seems too good to be true at this mileage, so…

This weekend I checked the amount of timing chain stretch using the dial gauge method. What I came up with was a measurement of 22 degrees BTDC (measured at the crankshaft) at 2 millimeters of valve lift on the intake valve. I rotated the engine through four complete cycles and came up with the same result each time. (Yes, I did remove all valve lash prior to making the measurement.)

According to the service CD as well as prior posts here, specifications call for 11 degrees. This of course *would* equate to 22 degrees at the crankshaft, but unless I'm mistaken the specification calls for 11 degrees *at* the crankshaft. Can anyone confirm what the proper specs are for this car? It is a 1984 300D, California version. It seems pretty far-fetched, but does the California version have a different camshaft than the Federal cars? (To meet pollution regs?)

ANY input from you guys out there in cyberspace is greatly appreciated, as always!

Book says "value on balancing disk" whatever that is.

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I'm sure that value on balancing disk means at the crankshaft damper pointer.

Good luck,

I recently went thru this process when I was re-assmebling my OM616 engine... I agree with Larry the specs refer to the crank pointer.

I have never understood how you can guage the amount of chain stretch by looking at the crank pointer and the assembly mark on the camshaft. Evertime I have checked an OM61X the two marks appear to be in perfect alignment... its only by using the dial guage method that I can tell how much stretch exists.

That said I've never seen an engine with 11 degrees of stretch. The most I've ever seen is 7-8 with 2-3 being more typical.

I guess what I'm trying to say is that I don't think the 'lining up the marks' approach to measuring chain stretch is a reliable way to determine if, or how much a chain is stretched.

Good luck - Tim

The chain is probably not stretched 11 degrees, if at all. The 11 degrees is the point at which that valve has the lift according to specifications. If the chart says 11 degrees, and instead you see 8 degrees, this would indicate 3 degrees of stretch.

Good luck,

The *really* odd thing about this is that the reading I’m getting is 22 BTDC. This would indicate that the cam is *advanced*, not retarded (?!). Maybe I’m just being a bit retarded for not being able to figure this out?

RTH

Well I'm really confused now....

In your first post I saw that you said 22 BTDC but I thought you have misspoke and meant 22 AFTER....

If you had 2mm of valve lift at 22 before TDC its seems like you would not have much compression in the cylinder when the piston reached TDC since the intake valve would be pretty open....Seems like you would also have pistion/valve collision issues to address.

Is it possible you are making the crank reading using the wrong side of the TDC pointer??? The reading should be made using the left side of the pointer... Another thought -- are you turning the engine in the correct direction?(clockwise, as viewed from the front)

Very odd, I'm baffled.

Larry

I was under the impression that as the chain stretched it would take more crank angle to produce a 2mm lift. This is why the specs for a new chain call for 9 degrees of crank rotation for a 2mm lift and 11 degrees for a chain with 20Km miles.

Am I missing something or are we mis-communicating??

Thanks, this is a great place to share expericences and seek clarification.

Tim

Yes, the reading I got was 22 degrees Before Top Dead Center & it was read off of the proper (left) side of the pointer. I eliminated the valve lash per the instructions on the CD. I set up the dial indicator properly & I was turning the engine in the appropriate direction. I haven't been banging valves & the engine compression is good.

If the cam lobe were worn, (which it isn't) it would only retard the action further. The only thing I can think of is that perhaps the valve lash is NOT supposed to be zeroed prior to making the measurement. I really don't think that's the case however. Perhaps someone out there can confirm whether or not the valve lash is supposed to be zeroed or left at normal specifications when checking.

I'm getting to the point where I think the rule "if it ain't broke, don't fix it" may apply, but it's driving me nuts not being able to figure this out.

Thanks again for the help everyone!

RTH

The valve lash should be reduced to zero.

I'm clueless as to whats going on here. I have done this procedure several times and have typically gotten results of 11 to 15 ATDC at 2mm lift, which as I recall was .0721 inches. Are you converting correctly? I know I'm grasping at straws here....

Sorry I can't be of more help

Tim

Did you check the cam timing. How about if it were advanced with offset woodruff. Or maybe chain is streched enough that camcould be advanced one tooth on camgear.

I hope it doesn't seem rude for me to say so, but for all this trouble that you've gone to in checking the chain, you could've spent about $65 and less time than you have already spent and just rolled in a new chain. It would be cheap peace of mind.

Good luck,

I'll second that motion Larry!!!!

Rob

Larry, it’s not at all rude at all for you to suggest that – I value your input. Truth be told, the only reason I haven't rolled in a new chain is due to the sprocket wear/adaptation issue. Being very knowledgeable do-it-yourselfers I'm sure that you're aware of the fact that when a chain stretches there is a corresponding wear pattern on the sprockets -- a certain amount of elongation. Thus when a new chain is rolled in there is a slight mismatch with the roller center-to-center length vs. the worn sprockets. While this is not really *that* big of an issue, it does cause slightly accelerated wear. If my existing chain is not stretched I would rather not change it. Then again, perhaps I am just rationalizing a way to avoid doing it. I've got a couple of other things that I would rather do to perfect this old beast & then I'll be completely done ‘going through’ the car.

The offset Woodruff key mix-up is something that I had considered, but I thought I was really grasping at straws (though at this point, I've got a handful ). The only way I could perceive this happening is if someone put in an offset Woodruff key to compensate for stretch, and then at a later date someone put in a new chain, which would have cured the original stretch & then the offset Woodruff would cause it to be overly advanced. Seems unlikely in a grandma driven & dealer maintained car with less than 200,000 miles, although you never know…

I am going to quadruple recheck the measurement just in case I was brain-dead on the day that I first checked it. If I get the same result, I will pull the sprocket to check on the key. Who knows what I’ll find in there.

Thanks Again Everyone!

RTH

I admire your analysis and ability to think the whole situation through.

I understand your hesitation in putting a new chain on old sprockets. Tell me, have you have ever raced or ridden off road motorcycles? The reason I ask is that the sprocket chain match on an offroad motorcycle is very important, especially if you're racing because if the chain drive is not right, it will chew up horsepower, and fuel.

Inside your engine is a much different situation. The chain in the engine is bathed in oil instead of dirt and sand like the one on your dirt bike. Maybe I just have been lucky, but I've never seen a visibly worn chain sprocket on a 616 or 617 diesel. They are double row and just over engineered for the application, particularly the four cylinder.

If you can visibly see elongated sprocket teeth, then you are probably correct in analyzing thoroughly, the bottom sprocket does not come off without removing the upper pan. The upper pan doesn't come off without removing the engine.

Good luck,