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Distributor timing question


Cudan

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Jocko...I may have different manuals than you have....my car manual is for Plymouth 1946-1954...my truck manual is for Dodge B-1 trucks. Here's my "paper trail" to get to the 7 o'clock position for the No. 1 spark plug.  In my car manual it gives pretty detailed instructions for installing the oil pump into the block. If these directions are followed, the slot in the oil pump (that the tang of the distributor fits into) will end up being in a horizontal position and according to the directions the engine will be at the top of the No.1 compression stroke.  Then if you install the distributor, the rotor can either point to the 7 o'clock or 1 o'clock position.  Either will work as long as you install the plug wires with No.1 over the rotor and in the proper firing order going clockwise around the distributor cap.  But here's where I get to No.1 being at the 7 o'clock position.  If I refer to the electrical diagrams in my manuals it shows the No.1 spark plug wire going from the plug and attached to  the distributor at the 7 o'clock position.  So if you install the distributor and the rotor points to the 1 o'clock position, pull it out a bit and rotate the shaft so the rotor points to the 7 o'clock position so it agrees with the published electrical diagrams.  Regards.

 

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Squirebill,

 Thanks for your detailed answer. I think I have a handle on this now. And since I still have the head and timing cover removed from the engine I can see how everything moves as I rotate the engine by hand. First things first. I made certain the timing mark on the crankshaft pulley lines up with the timing mark stamped on the camshaft timing pulley. With that, I know my valve timing is set. I then rotated the engine by hand until my #1 piston came up to TDC firing position and #6 at TDC between exhaust and intake. Here is what confused me for a while; No matter how I installed the oil pump I could not get the slot to be perfectly horizontal with #1 at TDC. I tried slipping teeth on the oil pump CW and CCW but no way would the slot line up to be horizontal. It would always be about 30 degrees off, up or down. So, just for good measure, I rotated the engine CCW a little bit until the oil pump slot became horizontal (that brought the #1 piston 5/8 inch below and before TDC). At that point the distributor rotor WAS at 7:00 and it lined up perfectly with my #1 spark plug wire.

 So from what I see, I believe that the #1 piston is actually before TDC (I measure it to be about 5/8 inch below TDC) when the #1 plug fires (oil slot horizontal & rotor is at 7:00). This makes sense to me since any given plug should fire before TDC, not at TDC. Am I seeing this clearly?

Jocko

 

 

 

 

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as assembly of the oil pump would be that of the maker there is no guarantee in my opinion that the 7 o'clock could or will be written in stone if this is a replaced unit....what you need to do is place its position as close to the 7 position as you can and ENSURE your distributor cap tower is indexable to this tower as the number one plug wire.....this is but a guide line for uniformity and should be followed as best possible to keep from getting mislead by yourself or anyone else that your timing is off by looking at this single indicator.  this 5/8 inch down is quite a distance from TDC in respect to degrees....

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Trying to wrap my head around what you are saying and believe you are one tooth off when installing the oil pump.  The drive gear on the oil pump has 10 teeth on it.  This means each tooth would be 36 degrees. (360 degrees / 10 teeth = 36 degrees/tooth).  As Plymouthy Adams states the 5/8 inch stroke down from the piston at TDC is quite a distance with respect to degrees.  I did a rough sketch of a circle with a diameter equal to the 4 3/8 inch stroke of the engine. If I come down the radius from 12 o'clock,then across from the radius at 90 degrees until I hit the circumference, I hit at about 40 degrees from the 12 o'clock position.  Maybe if i draw this all more accurately and actually use a protractor it would be the 36 degrees of one tooth on the oil pump gear.  Also there may be some additional geometry to account for the push rod etc.   So all that being said I think we have a case of the "tail wagging the dog" .  Instead of rotating the engine so the slot in the oil pump shaft is horizontal and the rotor points at 7 o'clock; you should set the engine with #1 piston at top of compression stroke and at  TDC and rotate the oil pump drive gear so the distributor rotor ends up pointing at 7 o'clock.  The instructions in my car manual basically say:  get the engine to #1 piston at TDC top of compression stroke.  Position the slot in the pump drive shaft in line with the two mounting holes on the oil pump.  Turn the drive gear "ONE TOOTH COUNTERCLOCKWISE" and carefully install the oil pump. Do not turn the drive gear when installing the pump.  I think we are talking about the pump  drive gear being only one tooth off.   Regards

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Thinking further on what Plymouthy Adams has said:  In the instructions the alignment of the slot in the shaft is referenced to the teeth on the drive gear.  If the drive gear is not installed in the same position on every oil pump it seems things could be off by a few degrees one way or the other.

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Plymouthy and Squirebill,

I think you guys are right after all.  I brought #1 up to TDC using the sprocket teeth markings as my guide to make sure I was there exactly. Then I moved the oil pump over by one tooth and brought the rotor to 7:00. (I also double-checked my point gap to make sure it is .020.) Then I connected my ohmmeter between the points and the block (ground) and adjusted the distributor housing until the points just opened. I should have read the Service Standards at the front of the electrical section in my Shop Manual. It clearly states that the #1 piston should be .000 inches from TDC when the points open. Then right below that it states the same thing again in terms of crankshaft rotation:  "Piston position when points open: TDC".

Jocko

 

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