timing

[yoshi]

Totaling confused with this timing stuff. SBC350, my engine was started & the timing was set at 33 i think, it was running with low vacuum. I turned the dizzy anti clockwise & i found the vacuum went up. I've left it at that but now my starter motor has fractured. I'm told it could be due to incorrect initial timing. Before i restart the engine I'll get a timing light sorted, but what i don't get is the initial/total timing thing. If you set the initial timing then set the total, your moving the dizzy so what's the point of doing the initial timing?

[dwcsr]

Initial timing is the only set of the distributor you do. You turn the distributor to the mark of 8 or 10 or what ever the book tells you. Total timing is a function of the vacuum advance and the fly weights in the distributor plus initial timing. That is checked with the timing light at the rpm stated in the tune up book. If you decide to change total timing you need to disassemble the distributor and change the weights and springs,this is called "re curving" the advance, usually its not an issue unless your doing a racing "curve" to the advance to change how the advance acts at a particular rpm. I would just set the initial timing and move on

[Gregski]

Originally Posted by dwcsr

Total timing is a function of the vacuum advance and the fly weights in the distributor plus initial timing.

That is incorrect, Total Timing is initial plus mechanical. No vacuum advance.

To keep things simple you disconnect the vacuum advance any time you adjust or check the timing, be it initial or total. Remembering to plug the vacuum hose of course.

[BIGglaSS]

Originally Posted by yoshi

f you set the initial timing then set the total, your moving the dizzy so what's the point of doing the initial timing?

33 at idle is way too much!

Too many variables involved with setting initial timing. For example, cam, idle speed, vaccuum, jetting, distributor curve, etc. These all affect idle speed. Change one of those, yet use the same initial number, then your total number will be different.

The book initial will not help you unless the engine is bone stock with the factory set distributor.

You're on the right track to set based on all-in (total). A good starting point is 32-34 total around 2500 rpm with vacuum advance plugged. After you set all-in, then take note of your idle initial as a reference point for future adjustment.

[Gregski]

Originally Posted by BIGglaSS

The book initial will not help you unless the engine is bone stock with the factory set distributor.

Amen, I totally agree, and it is highly doubtful our 40 year old trucks are still stock after all these years. I think the cam lobes wearing down over time can even effect the timing, so what the book says was good back in the 70's not no more

[yoshi]

I had it set at 33 but I had no vacuum so I turned the dizzy anti clockwise till the vacuum went up to about 12, I have no timing light at the moment

[dwcsr]

Originally Posted by yoshi

I had it set at 33 but I had no vacuum so I turned the dizzy anti clockwise till the vacuum went up to about 12, I have no timing light at the moment

watch this video it has all the info you need.
https://www.youtube.com/watch?v=UYGU7mTwsZc

and this if all you have is a vacuum gauge
https://www.centuryperformance.com/f...a-Vacuum-Gauge

[geezer#99]

I really hate when people tell novices or rookies to set there timing at 33 like that.
Rookies don't understand the total concept.
The best way I've ever done the timing is bump the initial up until your motor is hard to crank over when it's hot and then reduce your timing 2 degrees at a time until it's easy to crank. That way you know what your motor likes for initial timing.
You do want 32 to 36 all in timing near 3000 rpm. If you subtract your initial from the all in then you know how much timing you want in the dizzy.
There are several ways to limit the mechanical timing in the dizzy.
This link has a section on it. While it is an HEI the principles are the same.
http://www.crankshaftcoalition.com/w...EI_distributor
The other thing you need to confirm is your timing marks. By finding true #1 tdc.
Look here for that info.
http://www.crankshaftcoalition.com/w...op_dead_center
Every motor combo is different, but the principles are the same.
You need to confirm your timing marks, find your best initial timing and then adjust the timing in your dizzy.
Don't forget your carb is effected by timing changes. Increased timing also increases your idle efficiency and you need to slow your idle back down and adjust your mix screws to.
There's a section in that first link about that.
Best of luck to you!
Be patient!

[Gregski]

Originally Posted by geezer#99

Rookies don't understand the total concept.

Actually Total Timing concept is clearer to understand than initial because it is definate, ie rev the engine up to the point where the timing no longer advances, simple and black and white. Yes on some motors that could be 2,500 RPM on others 3,500 RPM but that's like an off on switch if timing does not advance between 2,500 to 2,600 RPM you have found your Total Timing threshold, ie ceiling, just read what the timing is at that point and you are done.

Originally Posted by geezer#99

The best way I've ever done the timing is bump the initial up until your motor is hard to crank over when it's hot and then reduce your timing 2 degrees at a time until it's easy to crank. That way you know what your motor likes for initial timing.

Geezer, I hear what you are trying to say, but how in the world do you define "motor is hard to crank" that is so subjective. Believe you me I want to know how to set initial timing but your method does not help me, I bet 10 different guys would pick 10 different "hard to crank over" points.

[1project2many]

Originally Posted by Gregski

Geezer, I hear what you are trying to say, but how in the world do you define "motor is hard to crank" that is so subjective. Believe you me I want to know how to set initial timing but your method does not help me, I bet 10 different guys would pick 10 different "hard to crank over" points.

I highly doubt that. Engines generally crank faster when warm than cold and properly adjusted carbureted engines should start faster when warm. If there's any question about whether or not the starter is laboring due to timing, disconnect the coil and crank the engine to get a baseline cranking speed. You don't need to split hairs over something that the least mechanically inclined of vehicle owners is able to identify as a reason to bring a car in for service.

[Speedbumpauto]

Before you say someone is incorrect you better be sure of your terms. Total timing is exactly that, total. If a distributor has a vacuum advance on it which affects timing, then what it does has to be measured in "total timing". For initial timing checks, even using the total centrifugal advance method, vacuum is not considered, but I guarantee anyone who has built a decent street performance engine that uses a vacuum canister knows how much timing it has and at what manifold vacuum that timing comes in. I think, as a group, we have finally had the time to engineer the simplicity out of what this guy needs to do.

[BIGglaSS]

This is one of those subjects that is hard to describe clearly through a keyboard, and I take for granted that the reader has a good concept of what is going on. Geezer, you're right, for a rookie, setting low initial at idle is the safer bet. And then, bump it up as needed. However the concept of setting total timing when mechanical advance is all-in, works on any engine because it takes the mechanical advance curve out of the equation. But, like you said, this method is probably better suited toward an experienced tuner, not a rookie.

Yoshi, a timing light is a good tuning tool to have. Do you know what dizzy you have? HEI, conventional, or points?

[Irishbleueyes]

Geezer is right on the money, easiest way to get best timing. Vac can is adjustable inside the vac port. Vacuum advance only works when your vacuum is high enough to pull it. The engine can handle hi timing advance at idle and under no load like cruising at part throttle. That will give maximum gas mileage and emissions. Thats why the method of twisting the dist till its hard to crank over works. Going to far ignites the plugs well before the piston reaches TDC and that puts resistance to the crankshaft hence hard to crank over. However when the vac drops off under throttle the mech advance takes over and climbs with rpm to match the engine needs. Pinging happens when the advance comes in to soon or to far for the engine to handle. Pinging can also be caused by glowing hot spots in the combustion chamber etc. This is something that is trial and error with every engine due to all the different engine combos. As suggested get an adjustable timing light to start then do some seat of the pants tuning. This will take time, be patient. Everyone has opinions on timing im sure this will get many hits.

[yoshi]

I've been trying to get the timing sorted today after fitting new starter motor. It took a bit of trying to get it started, I turned the dial on the back of the gun to 12 but I couldn't see the mark when I pulled the trigger on the gun & it looked like the balancer had stopped turning. I had to touch it with my finger to check ( I've never used a timing light before) I eventually found that the timing mark was further round, I turned the dizzy clockwise & the engine died. The battery wasn't strong enough to try again so it's on charge now

[1project2many]

It's very difficult for even a trained mechanic to catch some problems over the internet. In person it's possible to use all senses during diagnosis and repair. But through this forum we only have what's reported to us, which can make the job more difficult.

It's possible for the harmonic balancer's outer metal ring to move in relation to the center. This would move the timing marks and would lead to incorrect timing settings. It's also possible to put together a timing cover and balancer that are not designed to be together. This would also lead to incorrect timing settings. A person need to be sure the marks are in the correct location before using the light to set timing.

Many old timers would set the timing by ear, and / or using the vacuum gauge. This isn't a bad method but it can lead to confusion if the timing marks are incorrect and the timing is checked with a light. Right now you're trying to mix and match the two methods which isn't a great idea.

Additionally, unless you know what parts are installed in your distributor you don't know if someone has installed aftermarket weights and springs or a vacuum advance can. And if you have not checked the distributor for proper operation you don't know if the parts are working as intended. The distributor's characteristics are expected to be stock unless stated otherwise but without knowing, your internet helpers could be making wrong assumptions.

Also, we all seem to be assuming you have experience with a timing light but that's really not a good idea. Can you imagine how many hours we would all waste if you are connecting the light incorrectly? Do you have experience with the light? Are you connecting it to #1 plug wire to make measurements?

So, the plan:

First, in order to make sure that you and your helpers have a good foundation, assure that the timing mark on the balancer and the timing mark on the tab are aligned when number 1 piston is at TDC. That will allow consistent and correct measurements of timing. Second, determine whether or not you know how to use the timing light correctly. It's not difficult, just make sure you know. Third, set the distributor so the engine starts well and idles well. The method described, to set it so the engine just begins to crank hard then back off a couple of degrees, is acceptable. The distributor should be turned anticlockwise to increase advance, clockwise to reduce advance. Once the engine is running you can use the timing light to make measurements. The engine gets to decide what it wants for timing, not you. All you're trying to do is find the right numbers and document them so you can return the engine to those settings during tune-ups and after repairs. If the settings are extremely different from expected then you can determine why. But don't try to force the engine to run with different timing just because the measured number is not what's expected. When measuring timing, setting the dial at zero is the best way to start. If the spark is advanced of 0 degrees you will find the balancer mark appears to be is anticlockwise in relation to the timing tab. If the timing is retarded or less than zero degrees you will find the mark is clockwise of the timing tab. If the timing is advanced you can turn the dial until the marks line up and take a reading from the dial. If the timing is retarded turning the dial will not make the marks align.

And again, briefly.

Ensure the marks are correct.
Ensure you're using the light correctly (no insult intended, we just don't know).
Set the timing without the light so the engine starts and runs well.
Take measurements with the light.
Report.

And that's my contribution to this stew.

[yoshi]

Sounds good stew thanks, just a quick question, the vacuum at the front right on the carb is blanked off do I need to blank off the hose to the servo at the rear of carb? Thanks

[mr48chev]

If someone suggested 33 degrees of total timing that is 33 degrees of timing at around 3500 rpm and not at an idle.

It is where the mechanical and vacuum advance peg out and stabilize.


Your distributor has so many degrees designed into the mechanical advance at XXX rpm

The vaccum advance has so many degrees in it at yy inches of vacuum


The initial Seis what you set the rig at at an idle. Book calls for between 4 and 12 depending on what setup the engine has. the guys putting 33 or in that neighbor hood in aren't setting it at an idle though they are setting it with the engine running somewhere around 3500 rpm.

I'm not a fan of setting the timing by ear, leave that to Bubba and Leroy down at the spit and whittle club and do it the right way. You can set an old straight six 216 or 235 by ear pretty well but it doesn't work too well with newer performance engines from what I have run into.

[yoshi]

Ok I'm out here now working on my truck, I've removed the spark plug & I'm 100% sure it's TDC when the mark is at 0*. The rotor is pointing at number 3 plug & is sitting inbetween No1 lead & No8 on the cap

[_Ogre]

at tdc the rotor should point at 1 on the cap and sort of pointed at #1 cylinder
if your distributor won't turn that far to line up the rotor with 1 on the cap you may be off a tooth on the cam
that should get you close enough to start it

before starting pull the vacuum line of and plug it, start it and set the timing at 12 btc
run it, warm it up and turn it off, restart and if the starter kicks turn it back to 10
that's a good starting point, any wheres between 10 and 18 is good for initial timing

[yoshi]

I can turn the distributer clockwise & the rotor should line up with lead No1 on the cap. The vacuum at the front is already capped off, do I need to cap off the brake servo? It's too late now to continue plus the starter motor jambed so more shimming is required

[1project2many]

at tdc the rotor should point at 1 on the cap and sort of pointed at #1 cylinder
if your distributor won't turn that far to line up the rotor with 1 on the cap you may be off a tooth on the cam
that should get you close enough to start it

If the distributor drive gear is 180 out then the rotor can end up halfway between terminals.

I can turn the distributer clockwise & the rotor should line up with lead No1 on the cap.

Right, but there's more to it than that. You need to look at the position of the points / reluctor teeth (pointy triangle shaped things) to determine when the distributor will trigger the coil.

You shouldn't need to cap the vacuum booster.

[yoshi]

I've bought an HEI super coil distributer (big cap) but I can't fit it as I don't have the electrical connector to fit to it. I'm not sure that there is enough room as the air filter maybe in the way.

[OrrieG]

Just turning the distributor so the rotor aligns with the #1 plug terminal will allow the engine to run, but it might not be aligned with the timing marks. At Top Dead Center #1 piston is up, timing mark aligns with the 0 on the timing tab, rotor points to #1 plug terminal. Also you say the vacuum is plugged at the distributor?? When timing you plug the hose at the distributor end so the carb is not pulling vacuum.

If it is one tooth off you can usually get it to run but the timing mark will be way off. If it 180 out it usually will try and start but will not run, or will run poorly.

The harmonic balance looks like it is not turning because the timing light is lighting the mark every time the #1 plug fires.

[yoshi]

Carburettor is plugged not the distributer as there is no vacuum on the distributer. I drove the truck about a mile & it seemed to run fine, it was only when I stopped & restarted it that the starter motor broke

[yoshi]

Ok so should I turn the engine over so the timing mark travels 1 full turn then turn the rotor round?