timing and backfire

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Jun 27, 2005
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San Jose CA
'71 FJ40, '74 2F engine, Fireball ignition

It WAS running, but needed to replace the fireball ignition
Noticed a missing upper O ring on the dizzy
replaced, but it wouldn't let the dizzy drop down...O ring too big....replaced with a better fit.

got the TDC, confirmed with a test stick (fig 1)
The 2F manual shows: to turn the slot to point just past #4 plug (fig 2)
then turn the rotor to point towards #3 plug (fig 3)
when the dizzy is seated, the rotor points towards #4 plug, (fig 4)

Then I static timed it, ground and coil+ with a light
But when I tried to start it, it turns over but backfires

Am I missing something??
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tried to remove some pics, but they keep coming back..
 

Pighead

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Well, you could be 180* off or just a tooth off. I don't care where the slot on the oilpump is pointing, i only care to get the rotor in the right place when the dizzy gear catches the cam gear
 

Shark56

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Very simple test to see if you are 180 off.
Swap the wires, 1 to 6, 2 to 5, ect.
If you are 180 off it will fire. Might not run well but should run as long as the distributer is stabbed correctly.
 

Skreddy

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Pighead, ya lost me. I know I'm tired but what exactly do you mean? I know I'm not 180 0ff,
The crank rotates 2 times for each rotation of the distributor: the BB passes that window twice but distributor only passes the #1 cap terminal once. So Essentially, if you’re 180 out, the BB is on the wrong stroke. 1 and 6 are both at TDC at the same time but the valve orientation will only allow 1 of them to fire.
In short, looks right but might not be. Try swapping plug wires like Shark56 said, or spin the crank 1 more revolution until you see the bb again, then pull the distributor and put it back in per manual.
 

middlecalf

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If by chance you have the valve cover off when doing this, you’ll know your good to go with #1 at TDC on completing its compression stroke (which is essential) if both the intake and exhaust valve rocker arms jiggle - meaning both valves are closed.
 
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I get the 2 rotations and the 180
my confusion is.... TDC is when the #1 piston is at the highest point and the BB is visible. If the piston is not at the highest and the BB is visible then it's 180 from TDC.
I know I could check the valves, but the method I used should work. Right?

I did not pinch the vac, figured that was the next step or so. I just wanted it to fire up. It did with the biggest bang backfire. Uhoh...

I've repeated the installation from the FSM several times now. If things were a little off it should at least fire up and run ragged.

Pighead referred to the cam gear and rotor alignment. I think I followed the FSM for that.
The slot is moveable with a screwdriver. I don't know why the position matters. The cam gear is pinned to the rotor.
So, somehow I need to align the cam/rotor to some point??
 

73FJ40

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@fcgadget .
I get the 2 rotations and the 180
my confusion is.... TDC is when the #1 piston is at the highest point and the BB is visible. If the piston is not at the highest and the BB is visible then it's 180 from TDC.
I know I could check the valves, but the method I used should work. Right?

I did not pinch the vac, figured that was the next step or so. I just wanted it to fire up. It did with the biggest bang backfire. Uhoh...

I've repeated the installation from the FSM several times now. If things were a little off it should at least fire up and run ragged.

Pighead referred to the cam gear and rotor alignment. I think I followed the FSM for that.
The slot is moveable with a screwdriver. I don't know why the position matters. The cam gear is pinned to the rotor.
So, somehow I need to align the cam/rotor to some point??
Wrong! The #1 piston is at tdc at the end of the compression stroke (what you want) and at tdc at the end of the exhaust stroke. YOU CANNOT TELL WHICH TDC BY LOOKING AT THE BB! If this is confusing, search on "four stroke cycle".

I've found the correct tdc by removing #1 spark plug and using my fingertip to feel for compression while the engine is turned by hand. (removing all of the plugs helps with turning it by hand.)

If you are currently timed on tdc after the exhaust stroke, you could pull the dizzy and relocate the rotor 180 degrees and see if that works.
 

73FJ40

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@fcgadget .
I get the 2 rotations and the 180
my confusion is.... TDC is when the #1 piston is at the highest point and the BB is visible. If the piston is not at the highest and the BB is visible then it's 180 from TDC.
I know I could check the valves, but the method I used should work. Right?

I did not pinch the vac, figured that was the next step or so. I just wanted it to fire up. It did with the biggest bang backfire. Uhoh...

I've repeated the installation from the FSM several times now. If things were a little off it should at least fire up and run ragged.

Pighead referred to the cam gear and rotor alignment. I think I followed the FSM for that.
The slot is moveable with a screwdriver. I don't know why the position matters. The cam gear is pinned to the rotor.
So, somehow I need to align the cam/rotor to some point??

I find pigheads post to be misleading. The FSM instruction intends to ensure the blade on the bottom of the dizzy engages the slot in the OIL PUMP before the beveled gears on the dizzy turn the dizzy shaft counter clockwise. If the blade doesn't engage the slot, the oil pump won't pump, and your engine could be severely damaged in a matter of minutes once it runs.

I consider that confirming oil pressure is the first, most critical step in firing up the engine after reinstalling the distributor.
 
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pb4ugo

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I get the 2 rotations and the 180
my confusion is.... TDC is when the #1 piston is at the highest point and the BB is visible. If the piston is not at the highest and the BB is visible then it's 180 from TDC.
I know I could check the valves, but the method I used should work. Right?
When the bb is in the window the #1 piston is at or very close to the top of the cyldr. Always. As mentioned, on a 4 stroke engine you need to determine if it's on the compression stroke or exhaust stroke. As mentioned, the easiest way to determine which stroke it's on is to remove #1 spark plug and put your finger over the hole. When air is forced past your finger you are coming up to TDC on the compression stroke.
 

Pighead

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I have a different way of seating the dizzy to the oil pump. I line up the gears the way I want, then, with the cap on the dizzy, I stand on the tire, lean over and put one hand on the cap, putting a fair amount of weight on it...with my other hand I jump the contacts on the starter motor. Motor turns over, cam turns dizzy shaft and dizzy falls down into oilpump slot. You can feel the dizzy slide down that last half inch and hear a good thunk as it seats.

@fcgadget .


I find pigheads post to be misleading.
Sorry, that's just how i do it.
 
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WOW!
The 'stick method' I used pulls the #1 plug and puts a long dowel into the cylinder to 'feel' the piston rise.
It just determines that the piston IS at TDC, the compression stroke when the BB is visible.
I don't see how it could be anything but the compression stroke.

So, if it is at TDC, The FSM dizzy install should work?
line up the oil pump slot
position the rotor/gear
slide it in
check rotor orientation

after finding TDC by any method...If I ignore specific oil pump slot positioning and just drop the dizzy all the way in
and THEN just put the plug wires in the cap, lined up to the rotor according to the firing order
what would be wrong??
 

73FJ40

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@Pighead
This a truly a "Paul Harvey" moment, ("and now you know the rest of the story"). Your post #3 above lacks any real detail on your method, so you added your quote from a different, 12 year old thread to clarify. Your method is fine for someone who already knows the mechanics of the distributor/oil pump/camshaft arrangement.
@fcgadget has yet to understand that #1 piston (as well as the other five pistons) has TWO TDC's per cycle, and continues to avoid finding out the mechanics of a four stroke internal combustion engine cycle.

Your method is way to advanced for a neophyte.
 

73FJ40

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@fcgadget

Please research "four stroke cycle" on Google. Look at the piston position at the end of the compression cycle (as the piston continues traveling up to TDC) and also at the end of the exhaust cycle (where the piston also continues up to TDC), and then come back and report on which TDC you need to set your timing to fire the spark plug

Also note, that since the flywheel with the BB is bolted to the crankshaft that moves the pistons up and down, that the BB will show up in the window at both the TDC of the compression stroke and the TDC of the exhaust stroke.

You could also look at illustrations of the crankshaft gear that drives the camshaft gear and see that the camshaft gear has twice the number of teeth as the crankshaft gear. This results in the camshaft turning ONE 360 degree revolution for every TWO revolutions of the crankshaft. This results in the points and rotor only firing ONCE per cylinder for every TWO revolutions of the crankshaft.

If the points and rotor are firing the spark plug on #1 cylinder just near the end of the compression stroke (say, 12 degrees before TDC) you get proper combustion. If they are firing the spark plug on #1 cylinder just near the end of the exhaust stroke, you likely get backfiring.
 
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Pighead

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@Pighead
This a truly a "Paul Harvey" moment, ("and now you know the rest of the story"). Your post #3 above lacks any real detail on your method, so you added your quote from a different, 12 year old thread to clarify. Your method is fine for someone who already knows the mechanics of the distributor/oil pump/camshaft arrangement.
@fcgadget has yet to understand that #1 piston (as well as the other five pistons) has TWO TDC's per cycle, and continues to avoid finding out the mechanics of a four stroke internal combustion engine cycle.

Your method is way to advanced for a neophyte.
Well, yes. I have quoted my own post many times in many different threads over the years. I got tired of typing it. Figured everybody had seen it by now.
My apologies to the neophytes.
 

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