Supernaut72

I know I've touched on this once before long ago, but now that I've gone through the engine to bring it back up to par and finally got the remainder of the brake system fixed so I can drive the car regularly, I'm wondering about this once again: What timing should I be running? Particularly, in a place that regularly reaches the 100-115F range during summer time.

I'm running 5 degrees like the manual states, but the consensus last time I asked was that the factory timing was pretty conservative for emissions reasons. Thing is, we don't test for NOx here, only HC and CO, so I'm pretty sure bumping the timing wouldn't have a readable effect on emissions.

The main concern with the timing is keeping the engine happy at idle, there's a slight and occasional misfire in gear at idle only, which I'm thinking is a result of the timing not being advanced as much as it should be, barring 1967 emissions control measures. I've read that the comparatively lean mixture at idle and cruise burns a bit slower and likes a lot of advance, so perhaps bumping up initial timing a bit would help with that, in addition to cooler running and greater efficiency etc.

Yes, all ign components are adjusted to spec and are new. The engine runs fantastic, just want to help it out in this climate in any little way that I can.

Basically, I'm thinking of advancing to 7.5 degrees, don't want to go too far since I want to continue running regular 87 and don't want any risk of pre-ignition no matter how hot the engine gets with summer heat-soak or idling in traffic... But then, bumping the timing might help to prevent it from running quite as hot in the first place, I don't know. Would this likely be fine, or were the previous suggestions to bump the timing given with the unspoken footnote that I'd need to start running higher octane gas if I did so?

Fun71

I don't think Olds was overly concerned with emissions in 1967; at least not as much as they were in 1971 (and I regularly pass emissions testing). What you should be looking for is maximum mechanical advance at ~3000-3500 RPM, then let the initial be wherever it ends up. Be aware that increased initial timing WILL have a negative impact on HC and CO, but you can always set the timing back down for emissions test day then put everything back afterwards. I can give you pointers on tuning for emissions tests if you want as I have been doing that for over 15 years now.

If you have the original points distributor, you should be safe setting the timing a few degrees more than the factory spec, as long as you run the required octane fuel. One thing you could try is connecting the vacuum advance to a manifold vacuum port if it isn't already. This will give more advance at idle so the engine should run smoother as well as cooler.

A slightly more involved process would be to recurve the distributor to allow more initial advance while keeping the same amount of total mechanical advance. This would give more low RPM torque, increased performance, and (hopefully) not require higher octane fuel.

Supernaut72

I wasn't sure on the emissions thing, I've just heard that timing being further retarded than necessary was an early, early emissions countermeasure. Could be wrong.

Anyways I've seen lots of conflicting sources regarding whether the low compression engine is supposed to be at 5 or 7.5 degrees (some sources, including the csm say the high compression 2 bbl model is 5 and low-comp is 7.5). Would 10 initial be a good point to mess around with, in that case? I'm aware that the engine's from the early '70s sometimes called for 12 degrees but I'm not sure if there's any reason the earlier engines shouldn't go that high.

I have the distributor advance routed to the port on the carb that's on the corner of the float bowl

Fun71

Yes, retarding the timing was an early emissions thing but I don't think it started as early as 67.

The initial timing setting is the total mechanical advance minus the centrifugal advance. That's all.

If you set the total advance to ~34º at 3500 RPM or so (increase RPM until it stops advancing to find the max) then whatever reading you get at idle will be the correct initial setting.

The danger with arbitrarily increasing the initial advance is that you are also increasing the total timing, so if the total is already at 34 or 36 then increasing the initial could push the total up to a level where detonation could occur, especially if you are running low octane fuel in a hot environment. With that said, you should be OK advancing it 2.5 degrees (from 5 to 7.5). If your engine calls for 5 I wouldn't advance it to 10, though.

I'm not sure what port on the carb that is, but it's probably a ported vacuum source. You can check to see if there is any vacuum at idle. If not, it's ported. Connect it to a port on the intake manifold and that will provide full vacuum advance at idle and low RPM.

Supernaut72

Crap, stupid phone posted when I was half-done typing, before it totally locked up. Ain't technology great?

Anyways what I was in the process of saying was that the dist advance is hooked to that port on the float bowl casting, I'm not sure if the vacuum passage pulls from above or below throttle blades but it does bump the timing up to 18 or 20 degrees once it's hooked up.

I'm really not sure whether this engine is supposed to have 5 or 7.5, since I've seen some sources which agree with the CSM's 7.5 for low-comp and 5 for high-comp but other sources claim the opposite (here's one that says 5 is for high-comp 2-bbl). I advanced the timing to 10 and tried it out, but will probably go back and re-check for total. Will have to wait until I can acquire or borrow another timing light as mine conveniently decided to crap out today.

Anyways while testing it around town and on the freeway there was no audible detonation and it ran fine but seemed a little slow to get up and go when I matted it. Then again I'm running 2.73s so I'm not sure if it'd go any quicker with just a timing adjustment. After all, I'm driving a highway machine, not a 442. Power brakes did feel a little less mushy than when it was at 5 initial, so maybe that's a good sign.

Also fattened the fuel mixture by an 1/8th turn, I found that the porcelain on the plugs was light gray just barely going to beige. I'm thinking that the occasional misfire pop through the exhaust is just a symptom of running points (people don't switch to HEI for nothing). Doesn't matter to me, just wanted to be sure there wasn't anything wrong with it. The popping did seem to decrease a bit when I added a little more fuel to the mixture, so could have been just a tad lean as well.

Edit: On PC now, just noticed that you're in Phoenix. This engine passes emissions real well now that I've done a valve job but if you have tips and tricks for besting the ADEQ, I'd love to hear them. My '69 Chevy is having a lot of difficulty passing these days.

Fun71

OK, lots of items to address here and I'm working on a crappy keyboard so bear with me.


Sounds like manifold vacuum.

Well, my '70 Supreme with a 350 and 2.56 rear gears would burn rubber like mad and outrun a LOT of cars back in high school, so your 425 should feel peppy by comparison.

Also may be an indicator of an undiagnosed issue. With everything working as it should, your brakes should be strong no matter what the timing is set to.

That setting controls the idle mixture only and has no bearing on the AF ratio while driving, as in once you touch the throttle the carb is out of the idle circuit and the mixture screw no longer matters.

No, there is something else causing the misfire. If your points distributor is working properly, there is no noticeable difference when switching to HEI. Been there , done that.


Yeah, I can provide some help there. I find it ridiculous that AZDEQ emissions tests 50+ year old vehicles. Contact me and I can share what I have learned.

MDchanic

To all of the above, excellent responses, I will add:

You're going to trust an old Chiton's or Motor manual over the Chassis Service Manual?

Really?


- Eric

Supernaut72

It feels peppy, sure, just doesn't break traction unless you do a brake-stand. Does have posi, not sure if that has anything to do with it. Definitely throws you back in the seat a bit.

I think it was my imagination with the brakes. That, or I have to bleed them a little bit more and don't really notice until the fluid's been heated a bit. Just recently replaced the rest of the metal lines I hadn't gotten to earlier this year, did all four wheel cylinders and shoes, hydraulic hoses and all. Only thing I haven't touched is the master cylinder/booster but it stops without any pumping or diminishing pedal issues.

As for the ignition, I don't know, I've done everything possible. New battery, alternator, coil, points, cap, rotor, condensor, plugs, wires, everything. Dwell's set right at 30 degrees and has been checked and re-checked. Mixture was tuned to maximum RPM and then out another quarter turn beyond that. New vacuum advance and trans modulator, all lines checked for leaks. All electrical connections have been checked and re-checked, everything's clean and tight. Timing chain's been done. So, I can't see anything to fault for an occasional pop through the exhaust besides the points ignition system itself, though I admit maybe I'm wrong.

It's not frequent at all, just once in a while. Emissions test turned out lower numbers than my HEI Chevy ever did (after burnt valves were replaced, anyways) and the plugs have always come out good and clean any time I've checked them so the motor itself seems to be in good shape.

And yeah I agree about ADEQ. Haven't changed their car testing criteria at all since they started the program in '76. Talk about being stuck in the past, and not in a good way. I'll send you a PM about the emissions tips, thanks.

Supernaut72

CSM = Chassis Service Manual. I've made multiple references to it in my time here
Of course I have one, and of course I use it. It's the Olds manual that's telling me to tune my low-comp 2-bbl 425 to 7.5 degrees (and 5 degrees for high-compression 2-bbl, which I don't have).

I don't have a Chilton's or Hayne's for any Oldsmobile, never have and never will. If you're referring to the link above, that's an example of an alternate source that says the same thing as the 1967 CSM does.

MDchanic

Well, you posted a link to one above, and said that because it suggested 5° BTDC you weren't sure whether to go with it, or the CSM's recommendation of 7.5°.
In my book, that's taking the word of the Chilton's or Motor (or Haynes) over the CSM.

- Eric

Supernaut72

Huh? I never said anything about Chilton's, my friend. That above link agrees with the CSM, while most sources do not. If you notice, the timing spec for 2-bbl 425 is listed as 7.5, and the footnote says "high-compression 2-bbl, 5 BTDC". Now, here's a source that says 5BTDC for low-comp, 7.5 for high-comp, and it sure isn't Chilton's or Hayne's.

Here's another one that says 5BTDC for both low and high-comp 2-bbl. Clearly the information is all over the place and as I learned while doing the valves this year, the CSM is just plain wrong sometimes. In that case it told me to remove the driver's side cylinder head WITH EXHAUST MANIFOLD ATTACHED. This did not work out at all and broke the oil dipstick tube off, because the flared end of the stock, original dipstick was bigger than the gap between the stock, original manifold and head. Of course the bolts were rusted in and two were half-rounded so there wasn't much choice, but that's just to illustrate my point. The people who wrote the CSM were only human, so I always like to double-check now to make sure that I'm not seeing an error in it.

Ultimately it's a piddling difference I suppose, but I've heard many sources here and abroad say that Oldses don't ping as audibly as a SBC if you've got the timing too far advanced, and so I'm a bit cautious about timing specs given the hot climate this car has to operate in.

MDchanic

THe first link is definitely taken straight out of Chilton's, the second one is also Chilton's, I believe (I'd have to go out and dig out my old manuals to compare in order to be sure).

But you just made my point: You were debating whether to follow the recommendations in the CSM because they didn't agree with Chilton's. Don't do that.

- Eric

edit: Wait. Now I'm second guessing myself - one could be Glenn's

Supernaut72

Not to argue, but I wasn't driving at "this is correct and CSM is wrong", especially given that the first link 100% agrees with the CSM. My issue is with the way the CSM itself has messed me over in the past with editing errors. I don't hold other sources above it, generally. I've just learned better than to take its procedures and numbers in blind faith, particularly on matters that could burn pistons with pre-ignition.

For the record I am now tentatively considering 7.5 degrees to be the correct initial timing for my low-comp engine, even though one would think it'd be the other way around, with the premium fuel high-comp engine being the one that gets greater advance. Of course total timing could undermine all of that.

Glenn's?

MDchanic

Okay, then I misunderstood.


Why tentatively? If that's what the factory recommends, then that's the specification.
This is what I was talking about.

As for the reason, for one thing, the distributor advance specifications are different for both engines (LC is 5° more advanced at 2,000 RPM, for instance), so you can't compare the initial advance setting in isolation.
For another, it is likely that the low compression engine can run more advance, even at a lower octane, than the high compression engine, and still not detonate.

- Eric

Supernaut72

'Sokay, I worded it in a confusing manner. At first glance I see how it looks like I'm providing a link that contradicts the CSM, no I was providing one that agrees with it while others disagree.


I said above, it's because while the CSM is the Holy Book, it isn't without its flaws. I could very easily see an editor accidentally jumbling numbers in the timing spec table, mistakes happen. But, I'm definitely open to that not being the case, because I'm sure I'll find that the engine runs better at ~7.5 degrees instead of 5.

That's what I was looking for: A reason for the high-low advance figure difference that makes sense! Even if it's in part only a guess.
I agree that deeper dished low-compression pistons probably aid in preventing detonation even with greater advance and lower octane fuel, but I don't consider myself experienced enough to rely on my own ASSumptions regarding these sorts of things without consulting the far more knowledgeable people on here to do some fact-checking. So, thanks. 7.5 makes sense, especially in a hot climate that already stresses the cooling system enough, and given the low CR.


Edit: To add on to the idle misfire and general power issue I was talking to Kenneth about, I do have an air filter that's only got maybe 3000 miles on it, but was already very dusty when I last checked it. Consequence of living in a dusty, dry place. Forgot that I just tapped it out real good and put it back, since when I set out on a hellish quest to replace it a couple weeks ago I was given the runaround by multiple stores who claimed to have Wix 42097 in stock, when in reality they didn't. One store tried to sell me Fram CA328, the same filter that's in there now, before discovering that it's not even made anymore. Ran out of time, had to move that week and I guess that subroutine got lost in the commotion.

Will try changing the air filter tomorrow to see if that eliminates the misfire. Might even make the car spin tires again, after moving the timing up. As it is, when I tune the carb and then install the air cleaner housing I have to lean the mixture out 1/8 turn and raise the idle 50 RPM because the idle drops that much when I re-install the air cleaner. Don't recall it being that temperamental with adjustment when the filter was fresh, even with burnt valves.

Say what you will about the effectiveness of oil bath air cleaners, replacing some 50w now and then would be a lot more convenient than hunting down a new paper filter, especially now that one of two major providers of this particular engine's filter has completely stopped making them (I'm looking at you, Fram).

oldcutlass

IMHO, the recommended factory settings are a starting point, depending on your elevation, quality of fuel available, average air temp, etc... some tweaking may be required to optimize the engine performance and/or efficiency for a given time of year.

FYI, I trust Motors Manuals. Chiltons and Haynes not so much.

Supernaut72

Makes enough sense. I'm just tuning the car for all-around versatility, not really looking to squeeze every ounce of power out of it, just want to get it running how it should run. 5 degrees did seem to make it run hotter, run way worse after heat-soaking, etc.

Drove it all around in 90 degree weather today (a "cool day" for us ) and it didn't have any issues starting whatsoever after shutting it down and leaving it for 15-20 minutes at a time, like it used to. Under the same ambient and operating temp conditions it used to start right up just fine, but would then idle really rough and stall if put in gear if I didn't give it gas for about ten seconds or so.

Of course a new air filter made a world of difference, too. Forgot how dirty that thing was when I was trying to hunt down a replacement. Wix filter has far more pleats than that Fram junk so honestly I'm not too upset that Fram stepped out of the ring.