REFLECTOR: Lycoming IO 360 Timing

[Dave Dent]

You are right to a point.  But you must take into consideration gear lash
and pin looseness.  I am sure that with just the rivet on TDC  you would get
close enough for anything that would not cause any trouble to the engine.
These engines are very loose in the tolerances that it wouldn't make much
difference plus or minus one degree plus or two degrees minus.  But two
degrees plus could cause problems.  Like I said, "I was running 10:1
compression".  That is why I checked it with the meter.  But I'm sure with
Jeff's method of the pin in the case face to the gear you will be just fine
for your timing.  Some people just want it to the Nat's eye.
Dave
----- Original Message ----- 
From: "Jim Sower" <canarder at frontiernet.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Wednesday, August 25, 2004 5:15 AM
Subject: Re: REFLECTOR: Lycoming IO 360 Timing


> 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
> >
> >
>
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