How NOT to correct your 6.9 valve timing

[s class]

I have a lot of components removed from trusty rusty at the moment, and decided that before I close up, I should check the chain stretch. What a surprise I got. Have a look at the front cam bearing tower of the left head - someone in the past found that the timing mark didn't line up, and ground it off, and scribed a new mark.

So obviously I couldn't check chain stretch by the quick method of lining up the marks. I used the valve lift method, and found that :

The left cam is 8 degrees late (8 degrees on the LEFT cam - this chain is seriously stretched!)

The right cam is 2 degrees early - now to me this means the stretch is really 16 degrees, but the cam has been advanced by one tooth (18 degrees).



For comparison to see how that cam tower should look, I'll borrow one of styrias latest pics :

 

[Lukas]

Hi S Class,

For numpties like me that aren't familiar with this sort of thing, I take the the new "DIY" timing mark is the thin vertical (in the photo) line that is directly below the bolt head, and the removed line was somewhere to the right of it?

Also, is the line you match it up to the little notch in the brass-coloured fitting immediately below (which I assume rotates with the cam shaft)?

Ta

Lukas

 

[s class]

yes, Lukas, essentially that is correct. Problem is, the new line is not in the right place - its a few degrees off. The error is roughly as you see it in the photo.

 

[John S]

Has the line been marked to match up with top dead centre on the pistons?

 

[s class]

OK, I hope this makes sense.

THe line should indicate the alignment at TDC. I know from measuring the valve lift that the cam is 8 degrees late (ie #6 intake achieves 2mm lift at 20 deg ATDC, vs spec of 12 deg ATDC). PResently the lines do linr up with the crank at 0 deg, but this is with a stretched chain. When the chain is replaced, the line will be out by 8 degrees of crank.