I was wondering if anyone knew why GM changed the ignition timing marks on the crankshafts from the 1996-97 years and 1998-up, was there a performance reason? I would think if they wanted more ignition timing they could just change the parameters in the computer?

1996-‘97: These engines came with the 4618 casting that is virtually identical to the earlier 1237. They are both interchangeable.

1998-‘99: These engines still used the 4618 casting, but the timing notches were advanced by about 0.450", so the later crank can’t be interchanged with either of the earlier ones.

It’s easy to tell the difference between the two 4618 cranks when you see them side by side.

With both cranks facing you and the keyways at 12 o’clock, note the location of the notch at the top of each reluctor wheel. If the right edge of the notch is about .500" to the left of the casting seam and located around 11 o’clock, it’s the early, retarded crank.

If the right edge of the notch is right next to the casting seam and nearly straight up at 12 o’clock, it’s the later, advanced crank that came out in 1998. Don’t mix them up, or you will have a comeback.

That info is from "Everything you need to know about the different years for the 2.2L"
Thanks for the help!

Yeah, we know about it... It was done to stratify fuel-injection timing in conjunction with the new cam, so as to improve fuel-efficiency.


Go beyond the "bolt-on".