Camshaft Sprockets -> No Keyway; Timing Chain Stretch; Head Bolts

["Michel Drainville" <MDrainville@xxxxxxxxxxx>]

I'm in the process of removing the head on my 91 318ic (M42 engine) to
replace the profile gasket (GRRRR!)

While removing the camshaft sprockets, I realized that there are no keyway
to align the sprockets vs the cams like on an american engine.
I know the timing is completly done by the Motronic unit, but what leaves
me perplex is that each bolt hole on the sprocket is sloted. So even if I
position my camshafts using the alignment tools describe in the Haynes
manual (I use Haynes since my Bentley don't even talk about positioning the
cams or the tool to do it!!), and bolt on the sprockets, only the bolts
hold the sprockets in position, considering the fact that the holes are
slotted, is not a good approach to ensure that both cams will always be
"timed" refered to each other. I mean if one cam slips into the slotted
holes of one sprocket but not the other one, will that screw up the
timing.?

There was a talk about timing chain strech earlier. I found that my chain
had streched a bit. When the engine it at TDC, the two flats provided as
reference points on each cam should be on the same plane, but they are not.
The stretching of the chain made the cam to be dephased each other. I
suppose this will be corrected when I will reasemble everytning and
position the cam sprockets to compensate for that.

Is is mandatory to replace the head bolts with new ones? My engine uses the
Torx head bolts, like the 90-91 325.  In the past I successfully rebuilded
modified american engines using the same head bolts with success.


Thanks in advance
Michel Drainville
91 318ic

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