Setting total advance - '49 Olds' 303 V8

[Seedee]

Hey everyone, so I need some help in trying to wrap my head around setting up ignition timing on my 49' olds 88...

 

Now, I have tried looking at online videos which kinda helps but still confuses me and looking at the shop manual doesn't help either! I'm trying to see if setting the total timing will help cure my engine stumbling at high rpm. I have set the distributor at 0 and it's firing between the mark on the harmonic balancer @500 rpm. What kind of scares me is that the manual states the mechanical advance is all in  30* @ 3700 rpm! I would think it would be lower at maybe 3000

 

My question is that should I add the vacuum advance (20*) and the mechanical advance together and dial that in? At 3700 rpm? I'm probably thinking way too much on it! 

 

Here's the page from the manual if anyone can make heads or tails on this because I'm totally lost! I marked the section I'm talking about

 

[Ronnie]

The section of the manual you refer to seems to tell how the advance should work. Not how to set it.  Did you find a section for setting the timing?

[Ronnie]

29 minutes ago, Seedee said:

My question is that should I add the vacuum advance (20*) and the mechanical advance together and dial that in? At 3700 rpm? I'm probably thinking way too much on it! 

 

Generally speaking, on most engines you would disconnect the vacuum line from the distributor and plug the line before setting the timing.

 

 

 

Edited October 15, 2020 by Ronnie (see edit history)

[Seedee]

37 minutes ago, Ronnie said:

The section of the manual you refer to seems to tell how the advance should work. Not how to set it.  Did you find a section for setting the timing?

Unfortunately no, the only mention of how to set the timing is have the idle set and make sure the distributor is set at "0" and check on cylinder #1 that it's firing exactly between the two tabs on the balancer

Edited October 15, 2020 by Seedee (see edit history)

[joe_padavano]

Total advance is initial plus mechanical. At 3700 RPM, manifold vacuum is essentially zero, so there is no vacuum advance.

Why are you so worried about 3700 RPM?

[Seedee]

1 hour ago, joe_padavano said:

Total advance is initial plus mechanical. At 3700 RPM, manifold vacuum is essentially zero, so there is no vacuum advance.

Why are you so worried about 3700 RPM?

 

It just seems high to me that's all, I don't know if it just pertains to the 303s in particular if the max mechanical advance is at 3700? I was thinking it would be a lower rpm that's all...

 

So my main question is that to set the total advance....should I rev the engine to 3700 rpm, set the timing light to 30* and then turn the distributor so that the pointer is between the two tabs on the balancer?

[joe_padavano]

33 minutes ago, Seedee said:

 

So my main question is that to set the total advance....should I rev the engine to 3700 rpm, set the timing light to 30* and then turn the distributor so that the pointer is between the two tabs on the balancer?

 

You "set" total advance by modifying the springs and stops on the centrifugal advance weights in the distributor. Normally this is set at the factory when the distributor is built and is not changed in the field unless you have modified the car and need a different advance curve. You set the INITIAL timing per the service manual. If the distributor is in good shape, the total timing will match that factory spec (within manufacturing tolerances). Note that any wear in the distributor bushings, advance weights, or timing chain will alter total timing. You don't adjust this out, you fix the worn parts.

 

If mods to the engine or the use of less-than-optimum octane fuel require changes to the advance curve, your best bet is to do this on a distributor machine. You CAN do this on the engine, but it requires a degreed balancer or a dial-back timing light to check performance.

[Bloo]

 

1 hour ago, Seedee said:

So my main question is that to set the total advance....should I rev the engine to 3700 rpm, set the timing light to 30* and then turn the distributor so that the pointer is between the two tabs on the balancer?

 

To check total you would add the initial timing (whatever it is currently set to, as checked with your light) to the 30 degrees, and check that at 3700rpm. Vacuum should be disconnected and plugged. Look for the mark to be at TDC exactly. More likely you would use the buttons on the dialback timing light to line the mark up to TDC, and then read the actual number afterward off of the timing light.

 

To check vacuum, you would make a second run with a hand vacuum pump and put a whole bunch of vacuum on the vacuum advance. Should add about 20 degrees to your reading in this case.

 

OR- To check vacuum you could pull a bunch of vaccuum at idle with your pump and see how much the timing changes. Note the RPM. Now run the RPM up to the same level without vacuum. See how much the timing changes. Subtract your second number from the first. Should have about 20 degrees.

 

Timing tape is another way. The tape has to be the right diameter for the crank pulley or harmonic balancer. MSD makes a kit with a bunch of different sizes. Then you can see advance with a regular timing light (no dialback).

 

As mentioned by Joe, the best way is a distributor machine, but not many people have those.

 

Don't hold it at 3700rpm all day with no load on the engine. Make a real quick check and let it back down.

 

You can't compensate by just setting the timing if it is wrong at high RPM, at least no more than a couple of degrees. If it is wrong at the high end, and you reset it so it is right, it will be wrong at the low end. If it is way off, distributor work is necessary to correct.

 

1 hour ago, Seedee said:

It just seems high to me that's all, I don't know if it just pertains to the 303s in particular if the max mechanical advance is at 3700? I was thinking it would be a lower rpm that's all...

 

If you have heard of "all in by 20*" or something, that is done mainly with light cars in bracket racing and almost never with cars in more of a normal state of tune for the street. It doesn't work very well unless the engine has a huge cam and is running inefficiently at low RPM because of it.

 

A "normal" American v8 usually has a "compound curve", advance goes up real fast until 2500rpm (or so) and then slows way down for the rest of the trip. On older ones that don't rev real high, the first half may be a little slower or lazier, and the second slower half of the curve may not be present or necessary.

 

6 hours ago, Seedee said:

I'm trying to see if setting the total timing will help cure my engine stumbling at high rpm.

 

If I suspected that, before doing anything else I would first set the timing 5* retarded and see if it improves massively. Only pay attention to what happens at high RPM where you were having trouble. Then, set the timing back to the factory setting and disconnect and plug the vacuum advance and try again. It might run horrible, stall or bog at idle and/or low RPM but you can ignore that.

 

If neither helps it is probably something else.

 

 

 

Edited October 15, 2020 by Bloo (see edit history)

[Seedee]

Thank you so much Bloo! Your explanation of everything really cleared things up! 

4 hours ago, Bloo said:

before doing anything else I would first set the timing 5* retarded and see if it improves massively.

 

It's funny how you mentioned that...when I first got the car and really started to poke around the engine I remember seeing that the distributor was set to 5 degrees retard but never thought about it...but out of curiosity, why would retarding the timing improve driveability at high rpms? 

[Bloo]

The timing advances with RPM. It also advances with vacuum. If it should go too far for the compression, or the fuel, or the engine speed, or just too early altogether (piston isn't all the way up when the pressure wave hits) the engine will rattle or run rough.

 

It might detonate, ping, or just try to kick back on some firing impulses. If less timing makes it smooth out, too much timing (at that particular speed and load) is probably the issue. Otherwise. probably not.

 

Ideally, the centrifugal advance should track what the engine wants for maximum power at full throttle at any RPM. There is no vacuum at full throttle, so no vacuum advance.

 

At part throttle, the fuel charges burn slower, and the engine would like the fuel lit sooner to get the maximum good out of it. This is what vacuum advance is for, additional advance for part throttle operation. Just like centrifugal advance, too much vacuum advance will make the engine ping, rattle, or try to kick back on itself.

 

Since it is combined with centrifugal advance, but is a set amount of advance (20* in this case IIRC), there is going to be some problem RPM that limits how much total vacuum advance you can have.

 

Edited October 16, 2020 by Bloo (see edit history)

[joe_padavano]

And to add to what Bloo wrote, keep in mind that the factory vacuum and mechanical advance curves baked into the distributor were designed for the fuel available when the car was built. Today's ethanol-laced cat urine causes two problems. First, it's relatively low octane, which can cause pinging as mentioned above (especially in conjunction with 70 years of carbon build up). Second, the ethanol makes the mixture leaner than designed, which caused the engine to run hotter, which also contributes to detonation and may require different advance settings from original.

[Grimy]

Because of the lean condition occasioned by 10% ethanol gas, some pre-war car owners enlarge their carb jets by 0.002 to compensate.  You may want to check with OHV Olds V8 owners as to whether that has been tried, and what their results were.

[Marty Roth]

Despite "Common Knowledge" about plugging and disconnecting vacuum from engine to your distributor, both your manual, as well as w the one for my 1954 Cadillac, make no mention of disconnecting, and are in fact steel, rather than rubber hose lines. First, clean the points, filing only if necessary. Set the called for engine rpm, use your strobe timing light, and get the pointer to indicate midway between the two balls on the harmonic balancer. Then rev the engine and watch to ensure that this vacuum, as well as mechanical advance. Also, the tried and true method of static initial setting works very well. Bring the engine to the firing position in advance of TDC #1 cylinder (Pointer halfway between a balls), Connect a test light across the points so that it is "OFF" when the points are closed, and "ON" when the points are open. Turning the distributor clockwise so as to advance the timing before TDC, lock it down where the light just barely begins to light. This works for just about any car, and I even used it on several Citroens, and other vehicles where specs may not have been conveniently available. 

[Seedee]

18 hours ago, Marty Roth said:

Despite "Common Knowledge" about plugging and disconnecting vacuum from engine to your distributor, both your manual, as well as w the one for my 1954 Cadillac, make no mention of disconnecting,

 

I guess it's because it's assuming that our vehicles require no further adjustments other than making sure that both the distributor is set to 0 and that cylinder #1 is firing between the two marks. 

 

As far as other people saying it's also to do with our modern fuels are vastly different to the day that our cars used to run on started to make me wonder exactly what octane rating our cars ran on!

 

After digging on the internet I found a paper from the U.S Dept. Of commerce dated 1950 which talks about motor fuels and the various subjects, and in short...2 different octane fuels were available.

 

Premium - 80

Regular - 75

 

So, giving by that logic, timing would have to be advanced to compensate for the higher octane. I will however go ahead and retard my timing though to see if that cures my high rpm issue. Unfortunately I haven't had a chance to work on the Olds because of work

 

Here's the link to the paper, it's a really good read and provides a good insight to how fuels were back in the 40's

 

https://www.google.com/url?sa=t&source=web&rct=j&url=http://nvlpubs.nist.gov/nistpubs/Legacy/LC/nbslettercircular991.pdf&ved=2ahUKEwjjvOOsoLzsAhWRwFkKHVstCqwQFjAAegQIARAB&usg=AOvVaw3_BQrETKiOL0MVdibvCOun

[joe_padavano]

Octane isn't the only issue. Ethanol reduces the energy content per unit volume of fuel, so unless jetting is changed the mixture will be lean. This can lead to overheating and/or pinging.

[rodneybeauchamp]

From the manual you have provided, “In as much correct timing is 2 1/2 degrees BTDC”
This would be at 500rpm with vacuum advance disconnected and plugged as mechanical advance comes in at 600rpm.
 

That’s what I would be setting it at and be using a dwell meter And tachometer to set RPM and check and set the point gap.

Just my two bobs worth 😀😀😀😀😀😀😀😀😀

Rodney

[Marty Roth]

3 hours ago, Seedee said:

 

 As far as other people saying it's also to do with our modern fuels are vastly different to the day that our cars used to run on started to make me wonder exactly what octane rating our cars ran on!

 

After digging on the internet I found a paper from the U.S Dept. Of commerce dated 1950 which talks about motor fuels and the various subjects, and in short...2 different octane fuels were available.

 

Premium - 80

Regular - 75

 

 

Please note that Octane ratings back in 1950 were listed based on a different scale than currently used.

The current octane number scale is actually the simple average of two different octane rating methods—motor octane rating (MOR) and research octane rating (RON)—that differ primarily in the specifics of the operating conditions.

[Bloo]

13 hours ago, Seedee said:

So, giving by that logic, timing would have to be advanced to compensate for the higher octane. I will however go ahead and retard my timing though to see if that cures my high rpm issue.

 

You are correct, however I took 10 crankshaft degrees of centrifugal advance and 10 degrees of vacuum advance out of my flathead Pontiac to stop it kicking back on itself from too much timing. It met book spec before, and I fought it for a very long time because I couldn't quite believe it even though all the symptoms pointed to too much timing. The factory specs for the car have gobs of tolerance, but I am definitely out of spec now on centrifugal and almost out of spec on vacuum. It was so much too much that the 5 degree retard trick I suggested above to figure it out did not work. It runs terrific now. I note with puzzlement that my current timing curve looks a lot like what the Flathead Ford gurus are recommending for flathead Fords these days.

 

I can't explain it, as the gas was MUCH lower octane in 1936 when the car was made. Also others with different makes/models have had to advance the timing for modern fuel as logic would suggest.

 

 

13 hours ago, joe_padavano said:

Octane isn't the only issue. Ethanol reduces the energy content per unit volume of fuel, so unless jetting is changed the mixture will be lean. This can lead to overheating and/or pinging.

 

That is also correct. A modern car with an oxygen sensor will just richen the mixture to compensate and burn more fuel. Our old cars should logically wind up too lean. However, some of them were too rich in the first place, and even on cars new enough to have a pretty good fuel curve I have not run into one yet that I had to rejet richer. It surprises me and I can't explain it. The 1936 Pontiac is currently burning Ethanol laced fuel and I have it jetted 2 steps LEANER than stock. The leaner I went,the better it ran. I suspect I could get away with another step leaner.

 

My advice is to stick with factory spec until it is proven wrong. I have a sneaking hunch that when it is all said and done the 303 will prove to have some other problem.

 

 

 

Edited October 18, 2020 by Bloo (see edit history)

[ojh]

I've never messed with an old Olds distributor and it sounds like there are 2 seperate adjustments, the 'O' adjustment and the Distributor timing adjustment.  Maybe the 'O' adjustment is for winter/summer advance/retard? so you could change it without loosening the distributor? like it rotates the advance plate inside the distributor?  Reading the instruction to set timing it tell you to loosen the hold down plate and place the arrow to 'O' position and tighten bolt.  Then it tells you to start the engine and revolve the distributor to center the 2 balls on the balancer and tighten clamp bolt.  and: 'Note - see that the hold down plate arrow is in the center 'O' position'

Kinda tells me that the hold down plate is inside the distributor and is rotated around with the distributor body when the timing is set.  Once the distributor timing is set and tightened with the clamp bolt it sound like you can advance/retard it a couple degrees on the 'hold down plate' without loosening the distributor.

that right?

[Seedee]

On 10/18/2020 at 3:46 PM, ojh said:

it sounds like there are 2 seperate adjustments

It may sound like that by how the manual is worded but it's adjustment is pretty much like any other distributor, Loosen the hold down bolt and clamp bolts. The advance plate inside is held in place by 3 screws and rotates by either the vacuum advance arm or by the mechanical weights underneath...there is a piece of felt in-between the two plates the move by 3 ball bearings inside and lubricated with the felt. when I tore down the distributor and removed the advance plate I was surprised how spotless it was underneath given the amount of grime everywhere! The " arrow" the manual refers to on the hold down plate is actually a raised tab on the plate itself. I took a picture of the distributor (yes, I did retard the timing!! It was slightly more stubborn to start then before but idle seems fine when warmed up but slightly lazy when you blip the throttle

[bill pritchett]

Don't forget there is an Oldsmobile forum below this one if you go further down. They should be able to help you.  I have a 50 88 but do not timing so good luck.

[bill pritchett]

https://forums.aaca.org/forum/3-oldsmobile/ is the link for the Olds forum.

[ojh]

Thats an interesting distributor, thanks for the pics and explanation.  With the timing retarded the starting should have been easier and the motor would be lazy when blipping the throttle.

[Seedee]

23 hours ago, ojh said:

With the timing retarded the starting should have been easier

 It should be right?! Lol

 

I feel like maybe this thread is getting a little long in the tooth but that might just be me...either way, everyones input on this is quite the eye opener and learning something new is always good! 

 

Long story short....I just decided "you know what, to hell with it I'm just going to play with the distributor for giggles and see what happens! So i advance the distributor say, 3 degrees? And now the light is firing just at TDC...well it definitely has, let's say. "Awoken the beast" and any time you remotely give the engine any throttle it wants to tear your head off and fly down the road! But I still have it coughing up the carburetor and it feels flat as it climbs in rpm...

 

Which leads to either (A. It's running too lean, ala bore the main jets or maybe find an interchangeable one that's the next size up...OR... A vacuum leak hiding somewhere

 

Either way... At least I'm having fun tinkering with this and learning things along the way. 

[ojh]

Since you're playing around it'd be interesting to see where the timing is with a vacuum gauge attached, where you read the highest manifold vacuum while moving the distributor and back down a little, then compare it to where you are now.  I mention this method only because I question some of the readings you're getting - not saying you are doing anything wrong, its just sometimes old mechanicals indicators aren't where they ought to be and you're getting too many inconsistancies so the manifold vacuum method of setting the timing is just a way to confirm if the indicators in the book are right - if it comes back to anywhere close to what you now have then its' right, if the manifold vacuum method is way off then you know to dig deeper because you are dealing with the effect and not the cause of a problem.

I hope this makes sense to you, I hate getting 'wordy'.