> I guess I'm confused (not unusual) about the definition of spark
> scatter. Is it defined as errors in ignition timing
> 1. causing random fluctuations in the timing at a given cylinder, or
> 2. such that the cylinders are not firing at equal intervals (when
> fluctuations are averaged out)?
> Maybe it is a generic term which encompases both of the above.
To the best of my knowledge, it encompasses both of those. And you're quite
right, I was mostly looking at the first type.
> I'm not sure what problems could cause
> random fluctuations, but couldn't it be more than just wobble in the
> distributor shaft, e.g. timing chain issues, etc.?
Of course. But changing the pickup type wouldn't have much affect on timing
chain slack, camshaft endplay, etc. so I'm fairly certain my problem was
shaft wobble. Running with points showed a veritable light show, while it
was rock solid (except for my light occasionally missing a beat) with the
Crane.
> A while back I spent some time looking at the second problem. I believe
> that distributor machines can check this. It can be caused by an
> inaccurate cam lobe in the distributor or possibly inaccurate contacts
> in the cap.
Also a bent shaft will do it.
> You can get some idea of the problem by checking the timing
> at both cylinders which fire at the same crankshaft position, e.g. 1 and
> 4 on the four cylinder.
Shouldn't be too hard to mark BDC and check #2 & 3 as well.
> I've seen cases where the timing at these two
> cylinders were 2 or 3 degrees different.
AFAIK, 2 or 3 degrees isn't much of a problem. When it gets to be 5 or 10,
then you've (I've) got a problem !
Randall
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