M20 adjustable cam gear and setting base timing in ECU

[zaq123]

Since distributor rotor is cam driven and if the cam gear isn't set to zero, will it affect accurate timing verification with the timing light ?

[uturn]

I would like to believe the DME goes off the CPS signal to determine when to trigger the coil. The tip of the rotor is so wide that I'm sure it should take up any slop from the cam gear.

How wild are you advancing your cam or how much have you shaved your head/block?

[zaq123]

I did a little more reading after I posted this. Looks like cam timing doesn't really mater for setting the base timing in ECU as its strictly to sync ECU to the actual crank angle position. With that being said, anyone found a simple and accurate way to mark the crank balancer at 12, 20, 30 etc Advance ?

[hasa]

One triggerwheel tooth is 360/60 = 6 degrees.

[TobyB]

Nope. Spark is triggered off the crank, and that determines timing.

That said, if the distributor's too far off, the rotor will no longer be aligned with the plug tower contact when the coil fires,
and you'll get poor spark quality at large advances.
You'd have to be WAAAYYYYY off for that to happen, and the burn pattern on the rotor tip will tell you if it's happening.

The US M20 is odd in that the trigger and the distributor are divorced- in almost all other engines of that era, either the trigger was in the distributor base,
or they went to wasted spark, multiple coils. The intake design of the injected M20,
however, booted the distributor off the intermediate shaft... but they'd
already copied the Chebby strate sicks, and stuck the oil pump under the distributor,
so they had to leave the intermediate shaft and oil pump drive...
...wth sort of stemmy stuff were they smoking in the '70's, anyway???

t

[hasa]

Probably in U.S engines it was like that but Motronic 60-2 and distributor was common combination in Europe in 80’s.