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Originally Posted by insite
cloudsurfer: i initially planned only to CHECK if i could set timing without the tools. i actually used metrology shots to index the cams to the heads. after rotating the crank, i shot them again to make sure the cam hadn't turned. they didn't move even a sliver. setting TDC compression on bank 1 & TDC exhaust for bank 2 ensures that the cams are 'off lobe' and no valve springs are creating a polar moment. in this position, the cams actually 'WANT' to center on the timing marks. in fact, if you rotate the cams like 20deg one direction or the other, they will rotate back!
that having been said, it's pretty easy to eyeball the groove in the cams & the seam between the head & valve cover. the only concern for me at that point was whether the cams would move at all when i rotated the crank. they don't.
this is the only car i've worked on where the factory tries to get you to use all these holding fixtures. every other car involves us simply eyeballing the crank to a matchmark & doing the same thing w/ the camshaft. i find it hard to believe that only the porsche would be affected by thousandths of a degree here.
in fact, before i timed my motor, both banks were visibly off. jake says he sees them this way ALL THE TIME and that many are set improperly from the factory. IMO, the chains stretch over the engine life cycle, too.
it's not important to be PERFECT here, merely very good.
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All very good points. As I mentioned in another thread, I think the way the procedure works is less than ideal when you really think about it anyway. How much variation is there from pulley to pulley, as far as where that mark is machined and/or where the hole is to insert the locking pin? How much variations is there from cam to cam in terms of those slots being machined? There are several places where these potential errors can add up.
While it's absolutely true that the bulk of production car engines simply have visual marks to line up, and that's just what it is. However, on air cooled engines, you actually (or rather, the guys who really know what they're doing do so) time them by true TDC (dial indicator on cylinder 1 or 4) and split overlap method, which is DEAD on if you do it right.
No matter how careful you are timing an engine the M96 way, or visually (for most other engines), the best you're going to get is within a degree or two, which on a street car, admittedly, just doesn't matter. However, watch the race team guys and the cool looking tools they use....ya....their engines are DEAD on.
I'm still interested in solid lifters and "race" cams (no VarioCam BS) for my 3.8 and if/ when I find them or get them made, will time those via split overlap method with a dial indicator to determine TDC.