another short distributor thread, feel free to critique or adjust my reasoning...
09-11-2012, 08:20 PM
#1
Burning Brakes
Thread Starter
another short distributor thread, feel free to critique or adjust my reasoning...
I think my reasoning is based on experience, but until the last year or so I have not messed with Chevy distributors, other than my 91, and one 454 '68 Camaro with an '80 or so HEI.
the issue of setting timing came up recently, in a LONG thread, and several of us suggested the normal sequence of actions: #1 tdc compression, balancer set at 0, position dist housing the way you want it to be when bolted down, start dist into engine, turning rotor towards the #2 firing tab so that -when the cam and dist gears mesh, and rotor rotates CW- it will align with the approximate #1 firing tab.
of course, the oil pump shaft slot has to be adjusted to the same final position - since the slot is in the same centerline as the rotor- by turning it with a screwdriver, whatever, or by turning engine. -with the C4, I can easily turn the engine backwards via the 15/16 nut on the alternator.
anyway, a comment was that aligning rotor with #1 was incorrect, and that it should be aligned "between #1 and #8 plug towers." isn't it surprising that, after 50 year of distributors, there are so many opinions of how to set timing?
regardless of how you try to align the rotor, it ultimately has to be positioned directly in front of the firing tab -period. I think that the fsm wanted a general location to align the rotor, and it was simpler to say #1 and #8 rather than explain how to find #1 tab -who knows? (as a side note, the fsm says to position rotor between 1 and 8, THEN install distributor, which is not correct. the rotor will rotate out of position when installed, as we all know.)
I recalled that I had verifed, back in the '60's, that when you had the rotor in the "correct tooth" in the cam gear, it would always rotate about 28 degrees CW, since there are 13 teeth on the dist gear. so, that final orientation where the rotor stops, when seated, is the same for all SB, and BB, as far as I can figure.
.
the rotor is locked into the cam, and the dist housing is free to float wherever you want.
in other words, "between 1 and 8" is the same as setting the rotor to touch #1 dist tab -speaking only of the locked in rotor, of course. it is not possible to set rotor close to #8 or #1 as you drop it in, or to adjust it incrementally by a few degrees; it rotates 28*, and there it is. with the C4 HEI, timing marks aligned, the cam gears and dist gears are all identical, so the rotor should always be pointing in the general direction of slightly to the right of the center of the engine, between 6 and 5 on a clock face -your engine and mine, the same.
if your housing was positioned correctly, the rotor should be close to #1. the only way to change that location is to select another tooth on the gear, which will rotate it back, or forwards, by 28*.
I'm curious if this reasoning is flawed, for example, not all cam gears are always going to give the same results, or whatever. the 454 and my C4 reacted the same, rotor pointing to #1, cap aligned "square."
joe
the issue of setting timing came up recently, in a LONG thread, and several of us suggested the normal sequence of actions: #1 tdc compression, balancer set at 0, position dist housing the way you want it to be when bolted down, start dist into engine, turning rotor towards the #2 firing tab so that -when the cam and dist gears mesh, and rotor rotates CW- it will align with the approximate #1 firing tab.
of course, the oil pump shaft slot has to be adjusted to the same final position - since the slot is in the same centerline as the rotor- by turning it with a screwdriver, whatever, or by turning engine. -with the C4, I can easily turn the engine backwards via the 15/16 nut on the alternator.
anyway, a comment was that aligning rotor with #1 was incorrect, and that it should be aligned "between #1 and #8 plug towers." isn't it surprising that, after 50 year of distributors, there are so many opinions of how to set timing?
regardless of how you try to align the rotor, it ultimately has to be positioned directly in front of the firing tab -period. I think that the fsm wanted a general location to align the rotor, and it was simpler to say #1 and #8 rather than explain how to find #1 tab -who knows? (as a side note, the fsm says to position rotor between 1 and 8, THEN install distributor, which is not correct. the rotor will rotate out of position when installed, as we all know.)
I recalled that I had verifed, back in the '60's, that when you had the rotor in the "correct tooth" in the cam gear, it would always rotate about 28 degrees CW, since there are 13 teeth on the dist gear. so, that final orientation where the rotor stops, when seated, is the same for all SB, and BB, as far as I can figure.
.
the rotor is locked into the cam, and the dist housing is free to float wherever you want.
in other words, "between 1 and 8" is the same as setting the rotor to touch #1 dist tab -speaking only of the locked in rotor, of course. it is not possible to set rotor close to #8 or #1 as you drop it in, or to adjust it incrementally by a few degrees; it rotates 28*, and there it is. with the C4 HEI, timing marks aligned, the cam gears and dist gears are all identical, so the rotor should always be pointing in the general direction of slightly to the right of the center of the engine, between 6 and 5 on a clock face -your engine and mine, the same.
if your housing was positioned correctly, the rotor should be close to #1. the only way to change that location is to select another tooth on the gear, which will rotate it back, or forwards, by 28*.
I'm curious if this reasoning is flawed, for example, not all cam gears are always going to give the same results, or whatever. the 454 and my C4 reacted the same, rotor pointing to #1, cap aligned "square."
joe
Last edited by joe paco; 09-11-2012 at 08:24 PM. Reason: spelling
09-11-2012, 08:42 PM
#2
Le Mans Master
Doing this many...many years....I would agree with you that what you are trying to accomplish is to get the rotor pointing to the plug tower that is holding the #1 plug wire as close as you can. Then using the timing light you will dial in the correct timing.
Using the logic of getting it between 1 & 8 could be expanded the reverse and get it between 1 & 2 (last cylinder firing before firing on #1 again). So, either direction 8 or 2.....put the timing light on and rotate the distributor.
GOSH....to say that you are incorrect
.....guess this has something to do with the NEW MATH. You could explain it this way.....where as #1 tower is the "G" (goal) therefor G<8 and G>2. No the new math doesn't do it justice either....damn....just line it up with #1 and be done with it!!!!!!
Using the logic of getting it between 1 & 8 could be expanded the reverse and get it between 1 & 2 (last cylinder firing before firing on #1 again). So, either direction 8 or 2.....put the timing light on and rotate the distributor.
GOSH....to say that you are incorrect
.....guess this has something to do with the NEW MATH. You could explain it this way.....where as #1 tower is the "G" (goal) therefor G<8 and G>2. No the new math doesn't do it justice either....damn....just line it up with #1 and be done with it!!!!!!
09-11-2012, 08:53 PM
#3
Hi Joe,
Your reasoning sounds the way I always remembered it. I would think if you started the motor as the 'others' suggest (roughly 20 degrees retarded) may not even start. And you're right you'd never get it to adjust. AFAIK, it only fits in that "one tooth" and if it's off when in place you pull it back out, rotate the rotor a tooth over and reseat. This sure ain't rocket science, and people argue over this?
I would think you have conflicting comments because some are taking the fsm as the word of god. They may be good at research but never actually rolling up their sleeves and doing the actual work so thus the misinformation continues.
If the fsm had said to set it between 1 and 2 then all is fine. Perhaps just a simple misprint on the writer's part since 8 will be before 1 in a repeated numerical sequence and 2 comes after. That would be right if the firing order was numerical, but when we consider the firing order and that gets reversed.
Out of time for now...Regards,
Your reasoning sounds the way I always remembered it. I would think if you started the motor as the 'others' suggest (roughly 20 degrees retarded) may not even start. And you're right you'd never get it to adjust. AFAIK, it only fits in that "one tooth" and if it's off when in place you pull it back out, rotate the rotor a tooth over and reseat. This sure ain't rocket science, and people argue over this?
I would think you have conflicting comments because some are taking the fsm as the word of god. They may be good at research but never actually rolling up their sleeves and doing the actual work so thus the misinformation continues.
If the fsm had said to set it between 1 and 2 then all is fine. Perhaps just a simple misprint on the writer's part since 8 will be before 1 in a repeated numerical sequence and 2 comes after. That would be right if the firing order was numerical, but when we consider the firing order and that gets reversed.
Out of time for now...Regards,
09-12-2012, 12:20 AM
#4
Race Director
The problem I've seen with the FSM is that it was written by TECH WRITERS, not engineers or mechanics. I've seen some really good tech writers and some really ignorant tech writers. There are a LOT of mistakes in the FSM. For example, by '86 FSM shows a picture of the '84 heater core bypass valve, which is completely different than the '86. My FSM has pictures of CARBURETORS!!!
Joe, I think you're 100% correct in your reasoning. The end result (correct timing) is the important thing. How you get there is your choice.
Personally, I always point the rotor somewhere between 1 & 2 and it ends up pointing at 1 when the distributor drops into place. I've played with the oil pump shaft position, but I think it's easier to just bump the engine with the starter until the distributor drops into place. You can then rotate the engine around to #1 and check that everything lines up.
Joe, I think you're 100% correct in your reasoning. The end result (correct timing) is the important thing. How you get there is your choice.
Personally, I always point the rotor somewhere between 1 & 2 and it ends up pointing at 1 when the distributor drops into place. I've played with the oil pump shaft position, but I think it's easier to just bump the engine with the starter until the distributor drops into place. You can then rotate the engine around to #1 and check that everything lines up.
09-26-2012, 06:21 AM
#5
Safety Car
The biggest reason for pointing the rotor at #1 cyl (with #1 at TDC, compression stroke) is for the best plug wire routing. This position will only require two wires to route to the opposite side of the engine.
Any distributor position could still be wired for 18436572 firing order, but the wires will be criss-crossing the engine, and most will be longer.
Any distributor position could still be wired for 18436572 firing order, but the wires will be criss-crossing the engine, and most will be longer.
Last edited by Hot Rod Roy; 09-26-2012 at 06:25 AM.
09-26-2012, 12:22 PM
#6
Burning Brakes
Before I pull a distributor, I line up the timing marks to tdc, pull the cap and take a digital photo from straight above. Starts first time every time for me.
09-26-2012, 12:32 PM
#7
Le Mans Master
It's also important to keep timing chain slop/slack in mind. This is why you rotate the engine from the crank bolt in the direction of normal roation only. If you go backwards you need to move the mark more than 1" and then move the direction of ratation again.
You'd be amazed how much slop there is on a 100K mile chain.
You'd be amazed how much slop there is on a 100K mile chain.
09-26-2012, 01:54 PM
#8
Race Director
The biggest reason for pointing the rotor at #1 cyl (with #1 at TDC, compression stroke) is for the best plug wire routing. This position will only require two wires to route to the opposite side of the engine.
Any distributor position could still be wired for 18436572 firing order, but the wires will be criss-crossing the engine, and most will be longer.
Any distributor position could still be wired for 18436572 firing order, but the wires will be criss-crossing the engine, and most will be longer.
You can have #1 pointing to the firewall and the engine will still run fine as long as the spark plug wiring follows the correct sequence. There does not have to be an official #1 post on the distributor cap. #1 is relative to the rotor position at tdc on compression. It can be moved anywhere by chosing a different tooth on the cam.
09-26-2012, 05:44 PM
#9
Le Mans Master
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You can have #1 pointing to the firewall and the engine will still run fine as long as the spark plug wiring follows the correct sequence. There does not have to be an official #1 post on the distributor cap. #1 is relative to the rotor position at tdc on compression. It can be moved anywhere by chosing a different tooth on the cam. I usually install mine however is convenient for that engine/vehicle. If I am doing something that requires I remove the dist I mark where the rotor point currently is as well as the body to the manifold. Almost every time, as long as the engine doesnt turn over, I reinstall lining up the marks and the timing is super close or spot on.
09-26-2012, 06:49 PM
#10
Le Mans Master
I can't tell you how many times I have been called on to help a friend or family member that removed the Dizzy and could not get the car to run. I usually pull all the wires find TDC and wherever the rotor is pointing I use as #1. Ultimately the goal is to get #1 at TDC and the rest in their respective firing order. The problem is just about anyone can follow the FSM but they really don't understand what they are doing. Those of us who do know better.
09-26-2012, 07:05 PM
#11
Bottom line is that when you swap certain parts around like cams or even dizzys, there may be a slight timing difference, especially when there is a gear involved. it may NOT be perfectly set as the factory assembly line mass produced part.
BUT,
here is the other side to ign timing...and another reason why its adjustable...
To find the sweet spot in all engines.
I recently ran into something that I hadn't considered until a performance issue appeared.
I had a rotor that had its brass tip longer than it should have been and it was contacting the poles in the cap. Just a ticking as it passed each pole...easily heard thru the stetiscope. Anyway, I decided to "fix" it by grinding a hair off the tip. I also reshaped the tip accidentally and rounded the corners...
Now, I didn;t really consider this at the time, but what I had done altered the timing by a degree or 2. It made the rotor "late" in getting over a pole AND it changed the dwell (how long in position, duration)...again, easy to fix by a simple adjustment of the base timing but the dwell was gone forever with the 1mm of brass that I ground off.
Not a big deal by any means, but educational.
On another note, I have seen a different wire routing that moved #1 somewhere else on the cap and made wire layout somewhat easier and cleaner. No idea where that went but there is/was a [pattern circulating around here some time ago...
Trick to dizzy ins/outs is taking note of the amount of twist in the rotor as you pull it. Pay attention and get the "feel" for where it needs to be on insertion. When stabbing one in place, the goal is to END up on #1...so stabbing it a little behind is appropiate so the gear can turn as it seats. Its a matter of getting a feel for doing it and understanding that if you miss...it ain;t a big deal. Just do it again.
Good write up...keeps us thinking...(or trying)
BUT,
here is the other side to ign timing...and another reason why its adjustable...
To find the sweet spot in all engines.
I recently ran into something that I hadn't considered until a performance issue appeared.
I had a rotor that had its brass tip longer than it should have been and it was contacting the poles in the cap. Just a ticking as it passed each pole...easily heard thru the stetiscope. Anyway, I decided to "fix" it by grinding a hair off the tip. I also reshaped the tip accidentally and rounded the corners...
Now, I didn;t really consider this at the time, but what I had done altered the timing by a degree or 2. It made the rotor "late" in getting over a pole AND it changed the dwell (how long in position, duration)...again, easy to fix by a simple adjustment of the base timing but the dwell was gone forever with the 1mm of brass that I ground off.
Not a big deal by any means, but educational.
On another note, I have seen a different wire routing that moved #1 somewhere else on the cap and made wire layout somewhat easier and cleaner. No idea where that went but there is/was a [pattern circulating around here some time ago...
Trick to dizzy ins/outs is taking note of the amount of twist in the rotor as you pull it. Pay attention and get the "feel" for where it needs to be on insertion. When stabbing one in place, the goal is to END up on #1...so stabbing it a little behind is appropiate so the gear can turn as it seats. Its a matter of getting a feel for doing it and understanding that if you miss...it ain;t a big deal. Just do it again.
Good write up...keeps us thinking...(or trying)
09-27-2012, 09:20 AM
#12
Burning Brakes
I just replaced the dizzy in my 91...
The motor was timed at 6* before TDC and all i did was mark where the dizzy rotor was pointing at the firewall with a white out pen, then lifted the dizzy out and marked where the rotor pointed then.
For the reinstall, pointed the dizzy housing with the wiring coming out in the right place, pointed the rotor at the second mark I made, dropped it in and the rotor lined up with the first mark. Only snag is that my oil pump slot was not perpindicular to the oil pump "tang" so I rotated it with a screwdriver. Dropped right in, reset timing, and was good to go.
It is not hard but people really overthink it. If your rotor snaps and you want to put a new dizzy in, pull a valve cover, watch the valves, and get to cylinder 1 TDC on the compression stroke. Install the dizzy so the rotor sets at the cylinder 1 pole on the cap, and that means rotating the rotor back 30* towards pole number two so it ends up at the correct firing position. Set timing and you are set. People do not understand how it all works and that is why there are so many problems.
Mike
The motor was timed at 6* before TDC and all i did was mark where the dizzy rotor was pointing at the firewall with a white out pen, then lifted the dizzy out and marked where the rotor pointed then.
For the reinstall, pointed the dizzy housing with the wiring coming out in the right place, pointed the rotor at the second mark I made, dropped it in and the rotor lined up with the first mark. Only snag is that my oil pump slot was not perpindicular to the oil pump "tang" so I rotated it with a screwdriver. Dropped right in, reset timing, and was good to go.
It is not hard but people really overthink it. If your rotor snaps and you want to put a new dizzy in, pull a valve cover, watch the valves, and get to cylinder 1 TDC on the compression stroke. Install the dizzy so the rotor sets at the cylinder 1 pole on the cap, and that means rotating the rotor back 30* towards pole number two so it ends up at the correct firing position. Set timing and you are set. People do not understand how it all works and that is why there are so many problems.
Mike
09-27-2012, 12:41 PM
#13
Team Owner
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I've not yet changed a cam so this thread is interesting. With only pulling the dist to, say remove the intake base, I simply mark the base and put two marks on the dist circle, one before I remove it and the second just after the gear clears the cam gear.
09-28-2012, 03:25 AM
#14
Safety Car
09-28-2012, 11:05 AM
#15
Burning Brakes
Thread Starter
It's also important to keep timing chain slop/slack in mind. This is why you rotate the engine from the crank bolt in the direction of normal roation only. If you go backwards you need to move the mark more than 1" and then move the direction of ratation again.
You'd be amazed how much slop there is on a 100K mile chain.
You'd be amazed how much slop there is on a 100K mile chain.
the result is that the cap will appear to be rotated too far advanced even when timed to 6*, due to the additional 10*. the timing light is the final decision maker.
it's like changing wire locations: as long as you the owner understand it, it does not matter. the fun starts when you take it to a shop!
it is inconsequential, for me. rotating the engine with the alternator bolt is easier than using the crank bolt. a starter button would be ideal.
if there is another negative to it, I have not noticed it.
this is just a thread for discussion. none of it is too important. but there are tens of thousands of Chevy engines that still use a dizzy, so maybe someone will benefit.
joe