Cranking with Spark Advanced

[roccaas]

I try to strictly observe the rule to only engage the starter with the Spark Advance fully retarded (left lever UP).

Sometimes the old girl just quits at the stoplight. It must be the heat!

When I go to recrank, I sometimes forget to retard the spark because there is usually traffic behind me.

At these times, the starter cranks slowly (like it has a dying battery), but when I raise the lever up, the starter immediately starts cranking faster and harder.

When I cold crank the car, and have forgotten to retard the spark from the last drive (sloppy, just damn sloppy!), the starter also seems to labor compared to retarding the spark.

In consulting "DYKES" and Les Andrews, I do not see an explanation beyond the dreaded backwards crank of the engine in started with an advanced spark.

I do recall that Henry and Edsel put the piston's TDC just past vertical vis-a-vis the centerline of the crank, but is that enough to warrant a slow crank if the spark fires earlier than it should on start-up?

What is the mechanical reason that an advanced spark would slow the starter, and put more load on the starter (and battery?)

[1931 flamingo]

Not sure but mine reacts the same way and for the same reasons.
Paul in CT

[MikeK]

Originally Posted by roccaas

I try to strictly observe the rule to only engage the starter with the Spark Advance fully retarded (left lever UP). . . What is the mechanical reason that an advanced spark would slow the starter, and put more load on the starter (and battery?)

There is no other mechanical reason. It is strictly due to trying to compress a burning and expanding mixture before TDC. You can easily prove it to yourself: Remove the Hi-tension coil lead from the center of the dizzy cap and ground it. Now crank the engine and move the advance lever. There will be no change.

FWIW, my engine starts best a few clicks down, about 6 degrees advance, but I wouldn't do that with a weak battery that cranks slow or a hand crank! The "B" and all modern cars start with a small amount of advance, and it didn't break Bendix springs on those with that type of starter drive. A's are notorious for busted Bendix springs 'cause you can easily screw up and over advance when cranking. Do that several times and the spring weakens. Then it breaks when starting normally and people condemn the design.

[rotorwrench]

The starter will hold an engine from kicking back if the compression ratio is low (like a model A). If you are trying to hand crank the engine, your arm won't hold the crank as well as the starter does.

I had to replace a light weight (hitachi style) starter on an aircraft engine a while back that blew up due to malfunctioning starting aids on the magneto ignition. This particular engine has 10:1 compression. When it kicked back the starter pieced flew all over the place.

Thank God the little Model A is more forgiving.

Kerby

[Patrick L.]

10:1 ratio on an aircraft engine?? What kind of engine was it?? Impulse must have failed?? Was there an impulse on one or both mags??

[rotorwrench]

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Originally Posted by Patrick L.

10:1 ratio on an aircraft engine?? What kind of engine was it?? Impulse must have failed?? Was there an impulse on one or both mags??

It was a Lycoming HIO-360-D1A in a Hughes/Schweizer 269C helicopter. It uses the Bendix/TCM "Shower of Sparks" starting aid system on both mags with retard points at 5* advance (approximate). A lot of folks don't know to test them on inspections. You just have to wait until the owner/operator complains of hard starting or unitl the starter fails whichever comes first.

Kerby

[40 Deluxe]

10 to 1 compression?! Wow! What kind of fuel does it require? How long can it run at full power without meltdown? How rich?

[Patrick L.]

Well, you learn something every day.. I didn't know Lyc made anything with over 9:1 pistons.. I'll have to look into the 10:1's working in other 360's..

40 deluxe,, its hard to find any av fuel today other than 100 octane..

[antiquepa]

So You don;t forget I always put the spark control at the top when I shut her down. I have a 28 chrysler that is in the retarded position when down, so when I shut either one down I place the spark control in the proper position so I don;t forget...just my 2cents worth.

[steve s]

Originally Posted by MikeK

There is no other mechanical reason. It is strictly due to trying to compress a burning and expanding mixture before TDC. You can easily prove it to yourself: Remove the Hi-tension coil lead from the center of the dizzy cap and ground it. Now crank the engine and move the advance lever. There will be no change. ...

This is really interesting; I have wondered about this effect for years, although I never noticed it much with the Model A. I recall noticing in high school that kids who did a cheapo attempt at souping up of their cars by just advancing the timing, their cars invariably turned over real slowly, especially when the motor is hot--grunting like a nearly dead battery. What I still don't understand from Mike's explanation is that in my experience it didn't sound like the plugs were even firing when the engine was grunting along.

Steve