timing flat head
- Thread starter 4ford
- Start date
the question is how to time it?
Scott H in Wheaton
Well-known member
I guess it would help to know what kind of flathead and what year
Scott H in Wheaton
Well-known member
V8 Bob
Well-known member
The 8ba timing dots are all 2 Degrees BTDC (not 0) and is where I would start with your new 59A engine. Using an adjustable timing light will make this easy since you already know where TDC is.
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JSeery
Member Emeritus
4ford how did you determine TDC? Not trying to be over critical, but if you don't understand timing are you sure you understand how to determine TDC? It is important to get off to a good start on your new engine! Timing is before TDC and is normally in the 2 to 6 degree range on a flathead. The idea is the fuel takes time to burn and providing the spark prior to the piston reaching TDC provide time for the flame front to get started. As the engine speeds up this lead time needs to increase, called ignition advance. After about 2000 to 2500 engine rpm additional advance is not required. The initial timing and total advance depend on your engine, but around 4 degrees Before TDC (BTDC) for the initial and around 20 to 22 degrees BTDC total advance would be a reasonable stating place. Myself, I would not depend on timing marks I have not verified to assure where they really are in relationship to crank position.
JSeery
Member Emeritus
No, that will not get it accurate enough, but depends on what you are wanting to do. If you are just looking to find the beginning of the compression stroke that will work. However, it is very difficult (really not possible) to get the location within several degrees of where you want to be. If your crank pulley is already marked and you know what the mark is and you trust it, this would be OK. If you want to mark a true TDC you need to use a procedure something like the following to find it.
You will need a pointer attached to the block with a sturdy point near the pulley. You then need some type of hard stop in the cylinder to stop the number 1 piston against. This can be a little bit of a challenge with a flathead. Need to be carful to not damage anything, I would use something like a bent brass rod through a spark plug hole. You need to be sure it remains in the same relative area during checking. Turn the engine one direction until it comes up against the stop and mark the crank pulley under the pointer. Then turn the engine in the opposite direction until it again comes up against the stop and mark that spot. TDC will be half way between the two marks. That location needs to be permanently marked on the pulley (file a notch in the pulley). Because the engine passes TDC twice per four cycles, the valve positions are not relevant when finding this location on the pulley (it does matter when you are setting the timing). It would be a good idea to check it several times to be sure you are getting repeatable results.
This will give you a marker for TDC and would require a dial back timing light to determine the engine timing. Another approach is to measure the diameter of the pulley and determine it's circumference. Divide the circumference by 360 and that is the distance around the outside edge of the pulley for 1 degree. You can then mark it in degrees out to say 25-30 degrees or every 2 degrees or 5 degrees or just a couple of convent locations, what every works for you.
You will need a pointer attached to the block with a sturdy point near the pulley. You then need some type of hard stop in the cylinder to stop the number 1 piston against. This can be a little bit of a challenge with a flathead. Need to be carful to not damage anything, I would use something like a bent brass rod through a spark plug hole. You need to be sure it remains in the same relative area during checking. Turn the engine one direction until it comes up against the stop and mark the crank pulley under the pointer. Then turn the engine in the opposite direction until it again comes up against the stop and mark that spot. TDC will be half way between the two marks. That location needs to be permanently marked on the pulley (file a notch in the pulley). Because the engine passes TDC twice per four cycles, the valve positions are not relevant when finding this location on the pulley (it does matter when you are setting the timing). It would be a good idea to check it several times to be sure you are getting repeatable results.
This will give you a marker for TDC and would require a dial back timing light to determine the engine timing. Another approach is to measure the diameter of the pulley and determine it's circumference. Divide the circumference by 360 and that is the distance around the outside edge of the pulley for 1 degree. You can then mark it in degrees out to say 25-30 degrees or every 2 degrees or 5 degrees or just a couple of convent locations, what every works for you.
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BUBBAS IGNITION
Well-known member
OhioRick
Senior Member
Here's a good way to get it but the heads will have to be buttoned up.
A pressure/vacuum gauge screwed into the plug hole will get you a hair close to TDC.
Rotate the engine until you get max pressure at the compression stroke.
Then keep slowly rotating the same direction until you begin to get a vacuum reading at the exhaust stroke. Stop rotating then begin to rotate counter clockwise to find the sweet spot between pressure and vacuum. Moving the engine slightly in both directions will tell you if its at TDC.
Better than whistles and chasing bubbles in water tubes.
V8COOPMAN
Well-known member
With the heads off, you can determine TDC very accurately, and very easily. Make a strong, solid flat bar out of steel, approximately 1/2" thick, 1-1/2" wide, and approximately 7" long. Make it so that it can be bolted across the center of NUMBER 1 cylinder, using two opposing head bolt holes to hold the bar solid against the deck. Measure the distance between those two head bolt holes and drill them accordingly thru your metal bar.
One step left.....drill and tap a hole over the center of NUMBER 1 piston so that you can thread a bolt through the bar. The bolt should protrude about 3/4" below the bar when tightened, so that you can slowly rotate the crankshaft (by hand) until the piston just touches the bolt. Mark your pulley precisely via your pointer. Then, rotate the crankshaft the opposite direction until the same piston stops against the bolt again. Precisely mark the pulley again. The exact center between your two marks is precisely TDC. Same process mentioned above by JSeery, but much more accurate with head removed. DD
flatjack9
Well-known member
During the exhaust stroke, the piston is rising in the bore. I'm sure you meant power stroke. There is no way this is more accurate than having the heads off and using the positive stop method.