timing

[1project2many]

Originally Posted by yoshi

I can see the top of the piston through the spark plug hole with a torch

Yes, but how do you know it's at the peak of its travel? As much as ten degrees of error in the timing tab is difficult to catch when looking through the plug hole.

There are methods to determine very closely without special tools. To really do this correctly you need to make or buy a tool called a "piston stop." You could "eyeball" it if you can put a screwdriver or small rod on the piston through the plug hole. By turning the crankshaft manually, and slowly, with a wrench or ratchet and watching the rod for vertical movement, you might be able to confirm the timing mark is oriented correctly when the piston reaches TDC.

[Irishbleueyes]

Find a mechanic on CL and have him come over and give you a tutorial and get it set right.

[yoshi]

Cl?

[Irishbleueyes]

Craigslist

[imjeff]

Originally Posted by Irishbleueyes

Find a mechanic on CL and have him come over and give you a tutorial and get it set right.

X2. This sounds like it's gonna be a steep learning curve for you. "Setting by ear" and approximating TDC by visual of the piston are not methods that will give any degree of accuracy. Timing must be set with a light on confirmed correct marks, then the carb gets adjusted to meet idle specs. Different weights, springs and adjustable vacuum advance controls when total timing comes in, not so much about how much. The "correct" time for the timing coming in depends on motor, weight of vehicle, etc. and is not a cookie cutter spec. That is best done either on a dyno or timed runs. BTW, a dyno tune used to be the cheapest horsepower available.

Jeff

[1project2many]

Guys... he's in the UK. The world might not be the same on that side of the pond.

IMO we're not talking computer precision here. This is an attempt to get a reasonable timing setting that will allow for driving the vehicle without destroying a starter that was difficult to obtain. Any disagreement between expected timing values and measured once the engine runs can be diagnosed later.

[imjeff]

Originally Posted by 1project2many

Guys... he's in the UK. The world might not be the same on that side of the pond.

IMO we're not talking computer precision here. This is an attempt to get a reasonable timing setting that will allow for driving the vehicle without destroying a starter that was difficult to obtain. Any disagreement between expected timing values and measured once the engine runs can be diagnosed later.

While I did miss that he is in the UK, a quick internet search shows Craigslist is there as are dynos. The fact still remains that he needs to start with a timing light and piston stop, both of which should be available just about anywhere.

[1project2many]

While I did miss that he is in the UK, a quick internet search shows Craigslist is there as are dynos.

True. But I'm trying to approach this as if he doesn't have the same easy access to parts and resources that we're used to.

[OrrieG]

Originally Posted by yoshi

I can see the top of the piston through the spark plug hole with a torch

Could be on the exhaust stroke, not compression. You have a computer, find a Youtube tutorial for now, then order an old school (before 1973) Chilton or Motor manual that has the basic diagnostic sections in the back. They are reproduced. Might also look for an auto trade school text from then too. Over the years I have collected a bunch and inherited my dad and Orries. You need to get a clear grasp on the basics.

[imjeff]

Originally Posted by 1project2many

True. But I'm trying to approach this as if he doesn't have the same easy access to parts and resources that we're used to.

I think a timing light and method of verifying TDC is reasonable just about anywhere. I'm assuming timing lights are used in the UK. A dyno would be optimal, but not necessary.

[1project2many]

I think a timing light and method of verifying TDC is reasonable just about anywhere. I'm assuming timing lights are used in the UK. A dyno would be optimal, but not necessary.

That does sound reasonable. I suggested the piston stop but offered the rod method in case he wanted to make progress today and there's no chance to get the stop. A careful guy could use the rod. But he's got the light already and it's not too hard to build or have someone build a piston stop from an old spark plug and a bolt. If TDC can be established within 3 degrees that would be accurate enough for a mild engine. If you check timing on an old GM V8 with a high mileage engine and distributor there can be 4-5 degrees variation due to wear.

Once the engine is running ok I'd check base timing, vacuum advance at idle and off idle, min rpm for mechanical advance, and max rpm for mechanical advance. That's enough to plot a rough timing curve in case the engine doesn't like it.

If the numbers seem way off from what's expected, then it's time to start mechanical diagnosis on the engine.

Just dawned on me, and I can't believe I missed this, but if this is a points distributor he should be checking dwell or at least proper point gap before anything else.

[OrrieG]

I just use my thumb then back it off with a screwdriver in the plug hole until it top out. Check the timing marks, if somethings off a degree or two make a note and move on. Pretty sure the English have thumbs, if not they can put a banger in it and stop when it pops out!

1 project, that got past me too, timing and dwell are inter related, thats why they have the little door on the dist. cap. Will need a dwell meter to set that..

[imjeff]

Originally Posted by OrrieG

I just use my thumb then back it off with a screwdriver in the plug hole until it top out. Check the timing marks, if somethings off a degree or two make a note and move on. Pretty sure the English have thumbs, if not they can put a banger in it and stop when it pops out!

1 project, that got past me too, timing and dwell are inter related, thats why they have the little door on the dist. cap. Will need a dwell meter to set that..

Spot on. I didn't catch it was point type. Make sure you set dwell first. Every degree of dwell changes timing 2 degrees.

[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.

[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

[Race.it]

Just so you guys know in the UK we do have timing lights dynos etc.

Normally the issue here is locating a good mechanic, as we have a fair few Cowboys over here that can talk a good talk. The best way to locate somebody that can do real diag and timing etc is to get a recommendation or possibly a car club with similar engines.

Most garages these days here just plug the computer in and then if it don't plug in they charge you and send you on your way

I would offer to help yoshi myself but I am hardly in the UK now

[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.

[1project2many]

I think, as a group, we have finally had the time to engineer the simplicity out of what this guy needs to do.

I can remember something like this happening to me years ago. When I was about 13 I asked a few of the old guys at the local restaurant about dropping a distributor in my '28 Chevy during breakfast. What ensued was a 45 minute discussion about mags and cranks and gravity fed carburetors and point setting and 12 volt swaps and the farmer down the road and the farmer up the road and who knows what else. Eventually I came to the painful conclusion that it was a helluva lot easier to do it wrong 50 times than to sit and listen to a bunch of old geezers go on and on about a simple procedure without ever getting a definite answer.

Yoshi, you still with us "old geezers?"

[Irishbleueyes]

Timing article plus GM engineer write up

http://www.hotrod.com/how-to/additio...nition-timing/

Here's an interesting article on vacuum advance written by a GM engineer:

As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

[Speedbumpauto]

I stand corrected as per the engineer on the total timing definition. I will disagree with him on his dictum on manifold vacuum on any street driven car. Doesn't work that way on any serious street engines, especially at idle, but that's a discussion for a different day.

[yoshi]

Yes I'm still here, started a bit of a discussion by the looks of it. Got the truck started after a bit of dizzy twisting. I left it to warm up then rigged up the timing light, I couldn't see the timing mark at 1st then spotted it at the top. (12 o clock if using a clock face as an example) whichever way I turned the dizzy the engine didn't seem to like it & would die on me. I decided to find my piston stop well more of a guide as the bolt was loose in the spark plug. I sorted out a tap, tapped it out & screwed in a bigger bolt. That sorted I preceded to check the timing & it's ok. I also checked firing order on cap just to be sure. So that's where I'm at & still thinking of fitting the HDI

[Speedbumpauto]

There was a balancer made with the timing mark in that spot at TDC but it also had a timing cover with a scale in the same location. Miserable to check the timing as you had to look down between the water pump legs to see the mark. What happens is THAT balancer gets used with the more popular timing cover with the scale in the about 2 o-clock position and throws everything off that much. If your mark and scale are in the same location and it truly is TDC, then possibly(as mentioned) your ignition point gap or dwell is way wrong....if your distributor truly does have points. If it truly is a point type distributor and you have this TDC thing down, change it to the HEI and your problems could be over. Just make sure you mark the rotor position of the distributor before you remove it and install the HEI rotor in the exact same spot. Make sure the new distributor is fully seated in the manifold when the marks line up since these distributors have a nasty habit of not lining up the oil pump drive correctly during the install which will throw off the rotor position when you crank it over and the distributor does line up with the oil pump drive and drops down the last 1/2 inch and seats on the manifold. Been there.....done that.

[1project2many]

There was a balancer made with the timing mark in that spot at TDC but it also had a timing cover with a scale in the same location.

There are two applications that place the timing mark "straight up." 305 engines in 80's C/K trucks and vans made up to '95. Putting the "straight up" balancer with the timing cover having marks at 2:00 or 2:30 can result in timing being way off. The balancer and cover need to match.

Switching to HEI will bring some new issues. The original wiring is not large enough to properly power the HEI coil. I usually recommend a relay to supply power from battery to HEI through 12 gauge wiring.

Make sure the new distributor is fully seated in the manifold when the marks line up since these distributors have a nasty habit of not lining up the oil pump drive correctly during the install which will throw off the rotor position when you crank it over and the distributor does line up with the oil pump drive and drops down the last 1/2 inch and seats on the manifold. Been there.....done that.

If this happens I pick up the distributor, turn the rotor back one tooth, drop distributor, and repeat until oil pump alignment is correct.