How can advanced spark lever damage rod bearings?

[Texas Tom]

The September/October RESTORER has an article titled "Ignition Timing Dwell & Backlash." Very interesting.

At article's conclusion, author states: "All the way down on the spark lever would be too far advanced and result in damage to the rod bearings."

Questions:
1. Why would Henry design spark lever movement range that included a position that would damage bearings?

2. What -- specifically -- would the damage be?

[Marcus]

Tom - Thank you for posting: I was trying to figure the exact same information!! I was taught (and have done so for years) - lever completely up to start, pull completely down to run, and leave it alone. Both my A's operate (and have operated) exactly this way without damage or mishap....unless there is damage that is transparent to me! What say the guru's??

[BILL WILLIAMSON]

DON'T BELIEVE EVERYTHING YOU READ, unless it's from GOD! Just use COMMON SENSE.
Bill W.

[Bob C]

"For average driving the spark lever should be carried about half way down the quadrant. Only for high speeds should the spark lever be advanced all the way down the quadrant."

This is from the owners manual.

Bob

[pooch]

I could be wrong on this count so stand to be corrected..

But I think the window of movement on the distributor cut out section in its body is 20 degrees.

Because the cam is running at half speed, this 20 degrees at camshaft becomes 40 degrees at the crankshaft .

A full 40 degrees of advance is way too much for any engine.

On this second count I don't need any correction....

Too far advanced equals detonation of the fuel mixture and that is like hitting your piston with a hammer before it reaches top dead centre , and that transmits back down through the rods .

Fuel is designed to start burning before TDC, and make maximum combustion pressure at about 17 degrees after TDC .

Detonation means the mixture explodes very quickly and does not burn at the speed it should.

[700rpm]

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Originally Posted by Marcus

Tom - Thank you for posting: I was trying to figure the exact same information!! I was taught (and have done so for years) - lever completely up to start, pull completely down to run, and leave it alone. Both my A's operate (and have operated) exactly this way without damage or mishap....unless there is damage that is transparent to me! What say the guru's??

That's how my dad taught me in 1961. Dad was wrong. I ruined a good babbitt job in about 20k miles driving my Tudor like that.

[a-bone newby]

at low rpm 20 degrees advance will cause pre detonation when the piston still going forward its trying to push the piston in reverse so extreme pressure on rods

[BILL WILLIAMSON]

That's what I mean by using common sense, if it makes some unusual noises, retard it some. If lacking power, advance it a little. Your car will tell you if you're doing it RIGHT or WRONG! Model A's are very forgiving cars, they gave very good service, even when they were driven by every jackass member of a BIG family!
Bill W.

[700rpm]

Originally Posted by BILL WILLIAMSON

That's what I mean by using common sense, if it makes some unusual noises, retard it some. If lacking power, advance it a little. Your car will tell you if you're doing it RIGHT or WRONG! Model A's are very forgiving cars, they gave very good service, even when they were driven by every jackass member of a BIG family!
Bill W.

Voice of experience, Bill?

[MikeK]

If you encounter a long downgrade that causes you to rely on engine braking (compression braking) to limit your speed you NEED full advance. Less will cause engine heating, the same as running level too retarded. Later cars that included vacuum advance took care of this automatically.

If you think like a vacuum advance and work the lever accordingly your engine will see the least rod stress, be less prone to overheat, run the plugs cleaner, and deliver the best fuel economy.

Most guys find the detents on the quadrant levers worn smooth and have to restore them. I'm the guy that will (and has) re-worn restored lever detents back down to smooth again. Easier to fix that than a babbitt job.

[Mike V. Florida]

This is from an owners manual;

The Spark Control
For average driving the spark lever should be carried about
half way down the quadrant. Only for high speeds should the
spark lever be advanced all the way down the quadrant. When
the engine is under a heavy load as in climbing steep hills,
driving through heavy sand, etc., the spark lever should be
retarded sufficiently to prevent a spark knock.

[BILL WILLIAMSON]

Originally Posted by 700rpm

Voice of experience, Bill?

Yep, Ray, there wuz jist me & an old BLACK Dog in my family, But our neighbors had 8 boys & a '29 Tudor that never cooled off Fortunately, Chief taught them how to service it properly. They would leave their house, drivin' like Grandma, But Chief, with his hands cupped to his ears, could hear them "get on it" when they were about 1/2 mile down the woods road After their "getaway", they'd let the younger ones drive!!(SERIOUSLY, I DON'T make up these stories! If I made up stories, they'd be REALLY WILD!)
Bill W.

[pat in Santa Cruz]

Its amazing how many people just run the advance lever down after starting the engine. Anyone who has read the Instruction Book knows otherwise. But I have often wondered why the car was engineered to allow 40 degrees advance. My theory is that with the Model T, drivers learned how to feel the engine as the spark advanced and set it at maximum power. With a points system like a Model A has, as the points wear they close, retarding the spark. Having more advance on the register than is necessary with the points at .022 allows the driver to adjust the timing to maximum power as the point block wears and the gap closes, without having to re adjust the points right away. Of course, these days there are few drivers who can feel the engine as they advance the spark. Its a lost art.

[Purdy Swoft]

Damage occurs when the car is driven too slow and lugged in the higher gears with full advance. Slowing down and making corner turns in high gear without down shifting or retarding the spark as necessary to cushion the hammering effect. If you've ever choked a model A down in high gear you would have had to have noticed the bucking effect before the engine quit running. Of course this is the worse case scenario and the effect that hammers out the babbit. It doesn't have to be so bad that it actually bucks and quits running. The first signs is timing knock when climbing a hill and the engine begins to strain and lug or anytime that the car is driven too slowly in high gear with full advance. To avoid such situations ,don't creep up to hills or creep around corners in high gear and lug the engine. Build up speed when approaching hills to avoid lugging If driving at low speed when climbing hills when the engine begins to strain , retard the spark as needed and as the car slows you can feel the lugging cease and power seems to increase as you top the hills, this is of course on trails or roads like they had back in the day. This is what the owners manual is mostly talking about when describing the use of the spark. The owners manual doesn't really apply to todays roads and the higher octane fuel that we have had at least since the late thirties or early forties. If a person insists on driving at speeds of 35 or 40 miles per hour on the main highways they won't be able to maintain enough momentum-speed to climb some of the hills without lugging the engine with full advance in high gear. This is when some retard of the spark lever is needed. If a person really knows how to drive the model A in the first place they won't have problems driving at speed with full advance. The engine doesn't have to be run wide open all of the time to run with full advance it just doesn't need to be lugged with full advance. I have driven model A's with full advance without lugging for over fifty years with my model A's and still have the first one that I got in 1960 when I was 13 years old. I have overhauled this engine twice and it still has the original hard babbit . All bets are off with rebuilds that used soft babbit that contains lead. Cars with gear ratios higher than 3.78 are easier to lug and requires more driver skill. There is more misinformation out there about model A's than good. Many or most are actually confused. It seems that most are confused about backlash and can't correctly set the timing, much less correctly use the spark lever. Some try to follow the owners manual thats facts are out of date for driving on todays roads with todays speeds and higher octane fuel. I know that it is just a complete waste of time to try and explain any of this. There are a few that really know how to set the timing and drive the model a and many that never will. I'm not trying to hurt any feelings and it is none of my business what others believe or do with their model A's. The question was asked and this is my answer.

[Willie Krash]

On my bucket list is to meet Purdy......and Bill W. Well not Bill but his Dawg (that's the short list).

[tbirdtbird]

Totally agree with the man from Alabama; too many can't truly understand what timing is about. And I'd like to meet him, too, one day. He has much to offer here.

[bambooboy]

as a newbee,i skip over some advice,but pay close attention to purdy& of course tom w.----tom

[George Miller]

very good answer Purdy, right on.

[Purdy Swoft]

Thanks, Willie Krash-Mike , Tbird-Dave , bambooboy-Tom and George Miller for all of the Kind words !!!!!!!

[Mitch//pa]

dont forget me i love ya also.
you have the gift of giving real world experience thanks...