Timing changed after Cap + rotor swap?!

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DaveS

DaveS

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Hey guys,

i changed my cap + rotor on my ''74 Duster a while back.

my timing before the swap was 10 Before, now its 2 After.

as far as i know the timing cant change by changing a cap and rotor for a new set?!

dist. hold down bolt is nice and snug.. vacuum advance is not connected..

im complete in the dark to see 2* after with my timing light after a cap swap..

a buddy of mine suggest i accidentally misplaced all wires by 1 position to the right or left.. and thats about the only thing i could agree with what would make sense..

anyone?
 
Quality or mold differences for the cap maybe?
and or rotor.
Re-install the old cap see if it comes back.
 
p.s.: i changed everything else too, spark plugs, wires, coil, along with a voltage regulator and ballast resistor
 
Daves69 said:
Quality or mold differences for the cap maybe?
and or rotor.
Re-install the old cap see if it comes back.
Click to expand...

this
might even be able to get a 4th reading by installing the old rotor with the new cap


or...you may be able to loosen the snaps on the cap and clock it back to where it was

(als ik me niet vergis zit er altijd een klein beetje speling in, en als je maar 12 graden nodig hebt, zou het kunnen dat de oude distributie kap helemaal naar links zat, en de nieuwe helemaal naar rechts...of andersom)

as for your friends idea that each wire is one post of, thats a rather unsubstantiated claim (nice way of saying dumb)
assuming your working on a V8, that would put you off 45 degrees (60 if your working on a 6 banger) and i doubt it would run

which brings up the next question...what are you working on?
 
im working on a 318 V8.. engine runs pretty damn great, even better then with the old cap, then it used to backfire alot. (wich i think had more to do with the 42 year old ignition system than the whole timing thing)

engine is stock. runs on LPG (propane)
 
man, they put that LPG in everything there
here...we only run forklifts on it

did you have to have the valve seats reworked for that?
i seem to remember they take a beating with LPG

my money would be on production tolerances being off on the cap/rotor
if you undo the snaps, can you twist the cap a little?
 
haha, very funny ;)

yeah it has induction-hardenend valve seats.. so it should be able to handle the burn..

i can twist the cap half a centimeter about.. the snaps arnt that snug..

so you are saying i should take the snaps off, and then proceed to turn the cap to see what happens?

but isnt 12 degrees alot? like shouldnt i have to noticed 12 degrees change? especially being that it should run pretty good at 10 before (wich it didnt) and run worse at 2 after?(wich it dont)?
 
Cap and rotor don't determine when the coil fires.

Cap should fit snugly into a lock tab on distributor body.
 
yes, i think if you take the snaps off, you should be able to twist it and see if you can get back to 10 before, while still being able to line the snaps up

think about it, the circumference of the cap is what, 25 CM?
divide that by 360 and you get 0.069 cm per degree
that should put about 8 degrees in the half a centimeter you have

you should have noticed 12 degrees IF that was the only thing that changed
but with new plugs, wire, coil...you may be making up for the bad timing with better components

crackedback said:
Cap and rotor don't determine when the coil fires.

Cap should fit snugly into a lock tab on distributor body.
Click to expand...

correct BUT if the one rotor is on one end of the tolerance, and the other rotor is on the other end of the tolerance, it could play a part in it
think about it, when you loosen the distributor and twist it...what changes?
the cap in relation to the rotor


now keep in mind, im not saying twisting the cap is the way to fix this (the proper way to fix it is to loosen the distributor hold down and adjust it there)
im simply trying to brainstorm where the change came from
 
You shouldn't be able to move that cap more than 1°, that's about 1/32", less than 1mm. If it fits looser than that you have either an incorrectly manufactured cap, or the wrong cap for the distributor.
 
lets not discuss here if you can move the cap with the snaps on or of and stuff like that, lets keep this on topic. i think diymirage has a point here

by taking the snaps off and moving the cap is a very quick way of telling the timing, instead of fumbling a wrench all the way to the hold down bolt.. it sounds like a good idea to try.. worst thing that can happen is a backfire or an engine that stops running, i was thinking about the cap maybe having the points on a diffrent position too.. i will try the snaps-turn-cap-strategy
 
crackedback said:
Cap should fit snugly into a lock tab on distributor body.
Click to expand...

I agree. DaveS, I don't understand... how can you turn the cap? If you can, something is really messed up. The "snaps" you speak of do not radially locate the cap on the distributor.
 
im speaking about the 2 snaps that hold the cap on the destributor, they have a little play in them, allowing for maybe 2 to 2.5mm play in them each way, making a total of 5 mm play (for the americans here: thats 0.19 inch of play on the cap rotation with the snaps on) i know this doesnt account for much ignition timing.. but still..
 
For me, SOP is to reset timing with cap and rotor change. A 12° change does seem excessive though. Maybe around .290" on a 1.4" radius? Then too, who knows what's out there these days? How about the possibility of a balancer slip?
 
How about a vacuum leak that was corrected during the change? Possibly the vacuum hose to the vacuum advance canister?
 
Check the return spring for the vacuum advance inside the distributor. Even with no hose connected, if loose the mechanism can bounce around and move the timing.
 
The reluctor/pickup or points, etc determine firing of coil. The cap and rotor are along for the ride.

The mechanical advance could have been stuck in a slightly advanced position when static, now with dinking around, it's snapped all the way back to where it should have been resting. That vac adv one is an interesting deal.

Re-time the engine, check total and move on if everything is OK.
 
Daves69 said:
For me, SOP is to reset timing with cap and rotor change. A 12° change does seem excessive though. Maybe around .290" on a 1.4" radius? Then too, who knows what's out there these days? How about the possibility of a balancer slip?
Click to expand...

Comment withdrawn
 
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crackedback said:
The reluctor/pickup or points, etc determine firing of coil. The cap and rotor are along for the ride.

The mechanical advance could have been stuck in a slightly advanced position when static, now with dinking around, it's snapped all the way back to where it should have been resting. That vac adv one is an interesting deal.

Re-time the engine, check total and move on if everything is OK.
Click to expand...

I can't believe you had to say this once, let alone twice.
THE RELUCTOR POSITION IN RELATION TO THE PICKUP COIL IS WHAT DETERMINES IGNITION TIMING.
(Same with points and the points cam)
The cap and rotor have ZERO to do with timing but only relay the spark to the respective terminals inside the cap.
The produced spark is either in range of it's terminal or it isn't.

Think about this.
You can take the cap, rotor and all the plug wires out and your coil will still fire in correct time when the engine turns over.
This can even be verified by putting a timing light on the coil wire without it connected to the distributor and when you turn the motor over you will get four flashes per one 360 degree turn of the crankshaft. (Four flashes on your balancer with the light.)
ONE will be exactly where your base timing is set.

The cap and rotor only relay the spark and have zero to do with timing.

Also the engine would not have started at all if the plug wires were moved one place all the way around.
 
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I'm gonna throw a waaaay different theory out there. A new dist' cap wouldn't fix it if it jumped time.
 
IfItsGotWheels said:
When you adjust the timing by turning the distributor, what you are doing is changing the relationship between the cap [which is being moved with the distributor] & the rotor [which is not turning with the cap]. So if the rotor is in a different position, so is your timing.
Click to expand...

NO

You are changing the relationship of the reluctor and the pickup.

Simple question, what triggers/signals the coil? The rotor or the reluctor wheel?

If you believe the rotor does the triggering, why must some people do rotor phasing? Hmmm????
 
crackedback said:
NO

You are changing the relationship of the reluctor and the pickup.

Simple question, what triggers/signals the coil? The rotor or the reluctor wheel?

If you believe the rotor does the triggering, why must some people do rotor phasing? Hmmm????
Click to expand...
just damn. You need to look at that again.
 
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