High compression head and timing?
 

I have read that when using an aluminum high compression head that it is advisable to retard the spark a few degrees. Why is this? Is this for aluminum only or does it also apply to cast iron?
I have a cast iron 5.5 head and I don't detect any pinging or pre-ignition by running timing in the stock position.:confused:

Re: High compression head and timing?
 

Higher compression will give a faster maximum heat and pressure to the piston, so you need to use less spark advance, or damage may result.

Re: High compression head and timing?
 

When timing the engine how can I determine where to set the timing so it is not at full advance? Or should I simply raise the lever a click or two? This sounds like a guessing game.

Re: High compression head and timing?
 

Its best to use a timing scale bolted to the timing gear cover and a mark on the crankshaft pulley and a timing light and limit your maximum advance to 26-28 degrees.

Re: High compression head and timing?
 

I run a 5.5 head on all of my As and to get the timing right, I used a timing scale to guide me. On one car, I have an auto advance distributor so I set the timing in the usual way and take it for a drive. If I can make it ping, I retard the timing a little using the scale and repeat till I can't make it ping. I figure that if it doesn't ping when I try to make it, it will be pretty right for normal driving. I have found that about 7 - 8 degrees retarded at idle is close.
With the original driver controlled spark, it is just a matter of learning where it is happy. If it pings, move the lever up a notch or two. When you find the sweet spot, remember where it is and set the lever there each time you drive.

Re: High compression head and timing?
 

Lever full UP to start the engine.
As soon as it starts pull the lever down to the smoothest idle.
When driving, pull it down until you no longer feel an increase in power or smoothness. If it pings, then retard it some.

With my stock engine I pull the spark down about half way for idle, then while driving it's about 2/3 or 3/4 of the way down, and never all the way down, as that would be 40*, which is too much advance.

Re: High compression head and timing?
 

The owner's manual says to drive with the spark lever half way down, except for high speeds, when more advance is useful. With a high compression head, I set the spark lever at 9 o'clock and that is where it runs best.

Re: High compression head and timing?
 

I haven't heard any pinging.

Re: High compression head and timing?
 

You may not have the initial timing set at exactly TDC. It is easy to have it a few degrees ATDC. That buys you more room on the advance side, so you won't hear it ping or knock.

You may also just not be hearing the pinging, even though it is there. Under load, above all of the other engine noise, road noise, etc., it might not be so obvious to you.

A friend of mine ruined the babbitt on 2 of his rods when he installed a HC head because he was overdoing the spark advance and he never heard the engine ping or knock. After a few weeks of driving like this, he could hear the bad rod knock at idle. Too late. He had to rebuild the engine.

I have my initial timing set at exactly TDC. I have added a small stop on my spark advance quadrant that limits my total advance to 28 crank degrees (with a 5.9:1 BF head). That has proven good for everyday driving; I still retard it a few clicks when working hard, climbing a steep hill.

YMMV.

Oh, and you can't go by what the owner's manual says, once you install a HC head. You have changed the engine significantly and need to adjust for that.
.

Re: High compression head and timing?
 

Just because you do not hear pinging is no promise that the timing is correct. Today's gas is much better than it was in 1930, and you may never hear pinging, but still be too far advanced. Too much advance puts a strain on the rod bearings, and you can pound them right out with too much advance. I know this from experience. Experiment with the control while at speed and under slight load, and when you feel the engine is not running any stronger by advancing, stop advancing, and note where the lever is for further reference. Too much advance is bad, even without pinging.

Re: High compression head and timing?
 

I have a 7:1 alloy head on my car and the motor is very quiet. Consequently when it does ping, it sounds very loud.
With just a fraction too much advance (9:0 o clock on the advance lever), it will ping readily with just the tiniest bit of too much wellie.
The 41% overdrive F150 gearbox tends to exaggerate this problem too as it will pull up quite steep hills in overdrive, but one has to restrain one's accelerator foot and treat it very gently.

Re: High compression head and timing?
 

When a Model A engine pings, the sound is more like a bunch of ball bearings bouncing around in the flywheel housing.

Re: High compression head and timing?
 

Chris! Sounds ( or no sounds) like what your doing is good! Pulling your spark plugs and reading them will tell all. What causes pre ignition, a hot glowing spark plug, carbon in the combustion chamber, over rich or very lean fuel air mixture, over heated engine.
Go for a ride and get it warmed up, cruise at your steady cruise speed, push the clutch in and shut off the engine, when your stopped pull the plugs and read them. There's many places to see pictures of what your plugs should look like.
An advantage using a aluminum head is, aluminum dissipates heat faster than a iron head :-)

Re: High compression head and timing?
 

The thing is, an engine runs on heat. Heat from the burning fuel produces the pressure that pushes the piston down. The more heat the better, up to the point where it causes mechanical damage. You don't want to dissipate heat, you want it to stay in the cylinder and push that piston down harder (thus more power from the same amount of fuel, giving better fuel mileage and increased horsepower at the same time).
It's not that you can run higher compression with an aluminum head, it's that you need more compression to account for the heat dissipation! The advantage of aluminum is that it is cheaper to cast and machine.

Re: High compression head and timing?
 

I let the engine tell me where it wants its timing lever to be on my high compression head. While driving at fifty or fifty-five I minutely adjust the spark lever to see if my speed goes up or down to fine tune it. Nine 0'clock is where it likes to be at highway speed. It resists at 9:30 and 8:30 0'clock settings of the spark lever.

Re: High compression head and timing?
 

Stop the presses! I was premature on this. I didn't set the static timing with the dizzy body on, so it was off. I am working on the Mark 2 version now.

To use with my 6:1 head, I made this little clamp from a 1/4" coupler nut and an allen screw. The opening was carved with a cutting wheel on my dremel and dressed up with a file. After setting the spark with the lever up at TDC, I set the engine at 28 deg BTDC, using the Nurex timing strip. Next, I lowered the lever until the points opened and installed the little clamp against the lever. To check, I put the engine at ~35 deg, then confirmed the points opened when I rotated the engine to the 28 deg spot. The price was right for the clamp!



https://www.fordbarn.com/forum/pictu...ictureid=42550

https://www.fordbarn.com/forum/pictu...ictureid=42549

Re: High compression head and timing?
 

[QUOTE=Bruce of MN;1872563]To use with my 6:1 head, I made this little clamp from a 1/4" coupler nut and an allen screw. The opening was carved with a cutting wheel on my dremel and dressed up with a file. After setting the spark with the lever up at TDC, I set the engine at 28 deg BTDC, using the Nurex timing strip. Next, I lowered the lever until the points opened and installed the little clamp against the lever. To check, I put the engine at ~35 deg, then confirmed the points opened when I rotated the engine to the 28 deg spot. The price was right for the clamp![QOUTE]

Nice job on your timing stop Bruce. I have a Phillip's 'Automatic Automatic Spark Control' (similar to the Nu-Rex repro copy) on my Town Sedan that uses a similar stop. I have my total timing set at 28°. I set the spark control so when it is fully up it is @ ~5° ATDC so I can adjust full auto advance if needed. The lever for normal driving stays at 0° at idle.

http://www.fordgarage.com/pages/phillipsspark.htm

http://www.fordgarage.com/pages/nurexadvance.htm

Re: High compression head and timing?
 

iot

Re: High compression head and timing?
 

I edited my first post to say I was premature on this. I didn't set the static timing with the dizzy body on, so it was off. I am working on the Mark 2 version now.

Re: High compression head and timing?
 

You may want to do some searching on reading sparkplugs on the web.
Detonation has a pretty distinct mark on the plugs, easy to see.

John