Ryan,
I imagine that someone with the exact numbers will jump in & help. In
the unlikely case that no one does, I'll give the general method.
I'm not sure of your exact damper diameter. If it is 7 inches, where the
marks are, the 1" should be fairly close to 15 degrees. That is a pretty
big damper though. Multiply the exact damper diameter by 3.14 to get the
circumference, divide the circumference by 360 degrees to get degrees
per inch. This would give .915" for 15 degrees. If the damper is 6 "
diameter, 15 degrees would be .78". As you can see, it is important to
have the exact diameter which I don't know for your engine. I have read
other numbers of .080" for 15 degrees so I'm just not sure. But you
should be able to measure your damper. Stretch a cloth tape around it to
get circumference directly & skip the diameter part of the calculation.
The specs call for 15 degrees at 600 rpm but the advance is very
sensitive at low rpm, & the tach is not that accurate. It is hard to
get an accurate timing light idle setting.
A safe setting would be to measure total advance at 4500 rpm & set it to
35 degrees. Or just set it at 10 degrees static.
Some of the symptoms of retarded timing could be slow starting, though
fast cranking, loss of power, overheated exhaust system, overheated
engine. I have seen exhaust manifolds glow red hot with retarded timing.
The most obvious symptom of advanced timing would be engine kick back
against the starter when starting, & of course, pinging under acceleration.
Dave Russell
Big Sixer wrote:
> My Bentley book says set the timing for my BJ7 at 15 degrees BTDC. Which is
> great, but my vibration damper only has a little notch in it. I estimated the
> diameter of the damper and using a protractor, estimated that 15 degrees is
> about an inch on the edge of the damper, which I marked with a bit of white
> paint.
>
> Is that about right for 15 degrees? How have others determined what is the
> right amount.
>
> When I moved it to about 1" and 1/4 " it ran faster and a bit smoother, but I
> got some backfiring and a rumble that sounded like after burners. Also, the
> engine ran on after shutting it down.
>
> What's that all about?
>
> What's the story with timing?
> If it is too retarded, what are the symptoms?
> What are the symptoms for being too advanced?
>
> I've been working on cars for 25 years and still forget this stuff. I guess
> that's because the car hasn't been running for 8 years.
>
> Ryan
> BJ7
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