when cas is not in center of slot (rb26)

[syd_gtr]

I wasted a ton of time searching for topics on this so for the sake of people in future who may be searching, here are the reasons why if you look at your cam angle sensor it isn't in the middle of the slot. Tyndago has said on gtrusablog that if the cas is not at or near center on a stock car, you should be asking questions, and he is right.

Reasons

1. an aftermarket ecu can handle the cas twisted anywhere. You just have to set it up at the ecu in the mapping tables. So for example the cas may be deliberately positioned at what looks like max advance so that the owner doesn't muck around in a bad direction.

2. there is a cam gear and the exhaust cam has been adjusted, and the cas has been twisted to keep ignition timing the same rather than setting the ECU.

2a. the ignition timing is way off. and all is ok if the cas goes back to center slot.

2b. the cam belt is installed one tooth out and then the base timing was set. You now have 7.5 degrees of cam advance/retard

3. there is no cam gear and no programmable ecu but someone has decided they want to advance or retard ignition a little. The degrees twist from slot center is twice that number for ignition timing. So for example, a cas twist similar to "one tooth" out is most of the slot, and that's 1/48th x 360 x 2 = 15 degrees of ignition change.

4. there is no cam gear and no aftermarket ecu but the cam is aftermarket and the press fit locator inside the exhaust cam (looks like an offset slot, for R34, that is tilted somewhat with respect to the four bolt holes) is not quite right, so the CAS was twisted to get the base timing correct again.

5. the cas has a broken locator (meshes with the metal shape inside the cam) and this is causing all kinds of issues

6. the head and block have been machined and this changes the geometry slightly. I don't think this is worth much movement in the slot.

7. final answer. The stock sprocket has elongated bolt holes and locator hole and the bolts have been done up such that the cam is rotated from where it was supposed to sit, this is the backyard cam gear solution and you can't see it unless you either degree the cams and discover that with the sprocket marked tooth lined up with the backplate, the cam is twisted, OR, loosen the sprocket and see how much play it has on the cam. This final answer turned out to be my problem. I've seen this "backyard adjustable cam gear" mentioned for other motors, but could not find any threads on this for RB26.

Unless of course nissan stock cam sprockets all come with elongated holes? I don't think so, as they have the same part number for exhaust and intake and one of mine had elongation applied to all holes and the other just to the locator hole.

[niZmO_Man]