REFLECTOR: Lycoming IO 360 Timing

[Jim Sower]

Doesn't all this presuppose that the unit is installed (clamped to the 
accessory case) exactly where it is supposed to be?  Sounds like you're 
describing a test of the internal timing logic, but NOT the position / 
adjustment of the unit on the engine.  Like, if you loosen the hold down 
bolts and rotate the unit a couple of degrees, will that be indicated on 
the volt meter?

What am I missing here? .... Jim S.


Dave Dent wrote:

>As I wrote earlier, don't use a timing light. They are very inaccurate with
>this type of ignition.  They work good with a point system and some C/D
>systems but with the JR use a volt meter.  Just attach the red lead of the
>volt meter to the adv. of the computer and the black lead of the volt meter
>to ground and you can read the advance.  Be sure to do this with the vacuum
>disconnected from the advance box that is screwed to the top of the
>computer.  Plug the hose so you don't have a leak and then start the engine
>and you will be able to see what the actual timing is.  Your data plate
>should say 25 degrees before TDC.   If you don't see this on the meter,
>adjust it with the small adv. knob under the box.  This is the key piece
>that Jeff builds and adds to the General Motors computer and coils.
>
>The coils in the system fire both on the compression stroke as well as the
>exhaust stroke.  This is done by going through the ground side of the
>engine. The electronic system compensates for this but the timing light
>can't.  This seems to be the reason for the fluctuation in the light
>reading.  Giving a sense of jumping all over the place.  That is why I don't
>recommend using the light.  It will be just be pot luck if you get it right
>on.  There are a few timing lights that compensate for this but are very
>costly.  Good auto repair shops have them.  Volt meters are very cheap and
>do the job just fine.
>
>Dave
>  
>