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Flathead Fever · 06-01-2022, 11:59 PM

There is a factory precise setting using "distributor" rpm and vacuum for a completely stock '46-'48 engine. I'm pretty sure that is for setting it up on a distributor machine. Your advance will differ depending on the compression ratio, bore & stroke, carb jetting, camshaft choice, fuel octane, altitude, air temperature... Unless your engine is an absolute stock '46-'48 the factory setting will not be correct. The stock setup will work okay but it won't be dialed in for your engine.

I dug out 1949 Motor's Manual.

It says the initial timing is 4 Degrees. That will get bumped up on a go-fast flathead

Initial Advance Crankshaft is a minimum of 21 and maximum 24 at 3450 rpm.

contact points spacing .014-.016

Dwell at idle, left point's 50, Right point's 45-55, combined dwell 78-85. You set each dwell separately by sticking a piece of cardboard in the opposite one. The combined dwell will be 78-85. We always adjust dwell first and then the timing. Dwell changes the timing; timing does not change the dwell. We adjust the carburetor last.

Then they have a separate chart for the advance. This gets a little complicated.

"Vacuum Brake released" Distributer RPM that is "not" crankshaft rpm.
At 200 0-1 advance
At 400 6 1/2-8 advance
At 600 10 1/2-12 advance

Vacuum Brake on
At 200 0-1 with 0 inches of vacuum
At 1000 4.5-6.0 advance with 1.6 inches of vacuum.

1.6 inches of vacuum means the throttle is open pretty far so the vacuum break is retarding the timing to prevent detonation. It looks like most of the time that vacuum break would not even be doing anything until you were under a load. That is exactly why everybody says, under a load like climbing a hill back it off until it pings and turn it until it stops. Then its dialed in for your engine setup.

It always good to install a vacuum gauge in your car so you learn how driving conditions effect vacuum readings.

You "do not" need a distributor machine to set up flathead distributors but you do need a timing mark, which the earlier ones do not have. Anytime you have the heads off a flathead without a timing mark you need to make a pointer and mark the pulley at TDC and if you want at 4 degrees. Rotate the engine one direction until #1 is on TDC using a dial indicator and mark the pulley by your pointer. Then rotate the engine the opposite direction until #1 comes up and mark the pulley. In between those two marks is true TDC. You can file a little notch in the pulley and paint it white. If you have that one mark you can do all your flathead timing adjustments with an "adjustable timing" light.

Buy an "adjustable" timing light, never-ever buy a timing light unless it is an adjustable one. It allows you to measure how much advance you have by rotating a dial on the back of the light. Next you need a tachometer and a handheld vacuum pump. You can convert the distributer rpm specs to crankshaft degrees. You can use the handheld vacuum pump to apply the correct amount of vacuum, in this case 1.6 inches of vacuum to the vacuum break at 1000 distributor rpms. You "do not" need a distributor machine or KRW timing fixture and its actually more accurate to make the adjustments on the actual engine, but you must have a timing mark on the pulley. If you can always put the pointer on the side where the timing adjustment is on the crab distributor so you can watch the timing mark as you move the breaker plate adjusting the timing.

06-01-2022, 11:59 PM	#3
Flathead Fever Senior Member Join Date: May 2010 Location: Yucaipa, CA Posts: 1,360	Re: Crab Distributor vacuum brake There is a factory precise setting using "distributor" rpm and vacuum for a completely stock '46-'48 engine. I'm pretty sure that is for setting it up on a distributor machine. Your advance will differ depending on the compression ratio, bore & stroke, carb jetting, camshaft choice, fuel octane, altitude, air temperature... Unless your engine is an absolute stock '46-'48 the factory setting will not be correct. The stock setup will work okay but it won't be dialed in for your engine. I dug out 1949 Motor's Manual. It says the initial timing is 4 Degrees. That will get bumped up on a go-fast flathead Initial Advance Crankshaft is a minimum of 21 and maximum 24 at 3450 rpm. contact points spacing .014-.016 Dwell at idle, left point's 50, Right point's 45-55, combined dwell 78-85. You set each dwell separately by sticking a piece of cardboard in the opposite one. The combined dwell will be 78-85. We always adjust dwell first and then the timing. Dwell changes the timing; timing does not change the dwell. We adjust the carburetor last. Then they have a separate chart for the advance. This gets a little complicated. "Vacuum Brake released" Distributer RPM that is "not" crankshaft rpm. At 200 0-1 advance At 400 6 1/2-8 advance At 600 10 1/2-12 advance Vacuum Brake on At 200 0-1 with 0 inches of vacuum At 1000 4.5-6.0 advance with 1.6 inches of vacuum. 1.6 inches of vacuum means the throttle is open pretty far so the vacuum break is retarding the timing to prevent detonation. It looks like most of the time that vacuum break would not even be doing anything until you were under a load. That is exactly why everybody says, under a load like climbing a hill back it off until it pings and turn it until it stops. Then its dialed in for your engine setup. It always good to install a vacuum gauge in your car so you learn how driving conditions effect vacuum readings. You "do not" need a distributor machine to set up flathead distributors but you do need a timing mark, which the earlier ones do not have. Anytime you have the heads off a flathead without a timing mark you need to make a pointer and mark the pulley at TDC and if you want at 4 degrees. Rotate the engine one direction until #1 is on TDC using a dial indicator and mark the pulley by your pointer. Then rotate the engine the opposite direction until #1 comes up and mark the pulley. In between those two marks is true TDC. You can file a little notch in the pulley and paint it white. If you have that one mark you can do all your flathead timing adjustments with an "adjustable timing" light. Buy an "adjustable" timing light, never-ever buy a timing light unless it is an adjustable one. It allows you to measure how much advance you have by rotating a dial on the back of the light. Next you need a tachometer and a handheld vacuum pump. You can convert the distributer rpm specs to crankshaft degrees. You can use the handheld vacuum pump to apply the correct amount of vacuum, in this case 1.6 inches of vacuum to the vacuum break at 1000 distributor rpms. You "do not" need a distributor machine or KRW timing fixture and its actually more accurate to make the adjustments on the actual engine, but you must have a timing mark on the pulley. If you can always put the pointer on the side where the timing adjustment is on the crab distributor so you can watch the timing mark as you move the breaker plate adjusting the timing.